Title 24 · California Energy Code
Where does the code require Fault Detection & Diagnostics (FDD) and how is it tested?
If your nonresidential project uses packaged rooftop DX units or air handlers with zone terminals, the California Energy Code requires functional Fault Detection & Diagnostics (FDD) acceptance testing before occupancy (see § 120.5). The Appendix NA7 forms (MECH‑12A and MECH‑13A) specify construction‑inspection eligibility, fault‑injection steps (sensor disconnects, actuator failures, low‑air tests, refrigerant checks), sampling rules for terminal units, and who must sign the Certificate of Acceptance.
Last reviewed: July 6, 2026
What the code requires — plain English
The California Energy Code requires Fault Detection & Diagnostics (FDD) testing as part of the mandatory mechanical acceptance tests for certain HVAC equipment before occupancy. The controlling acceptance‑test list is § 120.5, which explicitly requires FDD functional acceptance testing for packaged DX units (NA7.5.11) and for air handling units (AHU) and zone terminal units (NA7.5.12).
The single most important rule: if your project includes packaged DX units or AHUs/zone terminal units covered by the acceptance list in § 120.5, those systems must pass the NA7 FDD functional tests before occupancy.
Requirements in detail
Summary of where FDD is required
- Packaged direct‑expansion (DX) units — FDD functional test required under NA7.5.11 as listed in § 120.5.
- Air handling units (AHU) and zone terminal units (VAV boxes, etc.) — automatic FDD functional testing under NA7.5.12 as listed in § 120.5.
Decision-relevant table
| Decision dimension | Required / value | What the acceptance test checks | Code Reference |
|---|---|---|---|
| Equipment types covered | Packaged DX units; AHU; zone terminal units (VAV boxes) | See separate test procedures below | § 120.5 |
| Packaged DX eligibility for credit | Unit must include factory‑installed features (economizer, direct‑drive actuators, certain sensors, TXV, refrigerant ports) | Construction inspection verifies factory FDD hardware and eligibility items | NA7.5.11 (MECH‑12A) — see E 805.12 construction inspection |
| Packaged DX functional tests | Low airflow fault, refrigerant charge verification, sensor calibration | Test steps: create low‑air condition; confirm FDD reports fault; verify refrigerant diagnosis; calibrate sensors | NA7.5.11 (E 805.12.1.2) |
| AHU FDD functional tests | Sensor failure/drift; damper/actuator faults; valve/actuator faults; inappropriate simultaneous heat/cool/economize | Steps include disconnecting sensors, cutting actuator power, commanding overrides and verifying fault reporting at control workstation | NA7.5.12 (E 805.13 / MECH‑13A) |
| Zone terminal unit sampling | Test one of each type; minimum 5% of terminal boxes must be tested (whichever yields representative coverage) | Functional steps: pressure sensor/tubing disconnect; damper stuck open/closed scenarios; verify control system fault reporting and recovery | NA7.5.12 (MECH‑13A) — sampling requirement explicit in forms |
| Sensor accuracy / required points (economizer FDD) | Temperature sensors ±2°F (40–80°F) where economizer FDD applies; permanently installed OA, SA, (and RA where differential control used) | Controller must display sensor values and indicate system status (economizer enabled, free cooling available, compressor enabled, etc.) | § 120.2(i) economizer FDD requirements — see NA7 references |
| Who performs tests | If required by Title 24, Part 1, Section 10‑103.2, tests must be performed by a Certified Mechanical Acceptance Test Technician (CMATT) | CMATT ID must be disclosed on Certificate of Acceptance | § 120.5(b) |
What the NA7 test forms look for (high level)
- MECH‑12A (Packaged DX / NA7.5.11): construction inspection checklist for factory FDD hardware eligibility; functional testing checklist with low‑air, refrigerant charge detection, and sensor calibration; PASS/FAIL criteria require all eligibility and functional test items to be “Yes.”
- MECH‑13A (AHU & terminal units / NA7.5.12): control‑station actions (no special instrumentation for AHU test), stepwise fault injections (sensor disconnects, actuator power loss, overrides) and sampling rules for terminal units.
Exceptions & special cases
- DDC‑based FDD algorithms: FDD algorithms implemented in Direct Digital Control (DDC) systems are not required to be separately certified to the Energy Commission (exception to certification requirement). However, the functional tests still apply.
- Factory‑calibrated economizers: Where an air economizer is factory‑installed and certified to the Commission as factory calibrated/tested, some functional testing elements may be excepted (this exception applies to the air economizer acceptance tests; check interplay when the economizer is part of an FDD system).
- No compliance credit but allowed installation: If an FDD system does not meet the eligibility or testing criteria, the code permits installation but no performance‑path compliance credit will be awarded. The system still must be documented and the acceptance test results reported.
If a specific detail you need (for example, exact MECH‑12A/MECH‑13A line‑by‑line checklists) is not shown above, that level of verbatim text is available in the Appendix E / NA7 forms (the files provided include the forms). I cited the relevant pages; tell me if you want the exact checklist fields extracted.
Common mistakes
- Assuming any FDD equals compliance: Projects often install an FDD-capable controller but skip the construction inspection eligibility checks (factory‑installed features, sensors, deadband limits). If eligibility items fail, the packaged unit can be installed but will not receive performance path credit.
- Missing sensor permanence or accuracy requirements: For economizer‑related FDD, OA, SA, and RA (where required) must be permanently installed and temperature sensors must meet ±2°F (40–80°F) accuracy. Omitting permanent sensors or using uncalibrated sensors causes failure.
- Sampling errors for VAV/terminal units: Testers sometimes test only a single unit and ignore the “one of each type and minimum 5%” rule for terminal boxes; that fails the NA7.5.12 sampling requirement.
- Not using a CMATT when required: If Title 24, Part 1, Section 10‑103.2 requires certification, an uncertified technician cannot sign the certificate — the code requires a CMATT ID on the Certificate of Acceptance.
- Expecting certification instead of functional testing: Certification of FDD algorithms to the Commission is required for some packaged‑unit FDD systems, but DDC‑based algorithms are excepted from certification — still, functional acceptance testing must occur.
Worked example — concrete scenario
Scenario: New small office building installs:
- One rooftop packaged DX unit, 5 tons (60,000 Btu/hr) with an economizer and factory FDD hardware.
- One AHU serving core spaces with DDC to zones and 10 VAV terminal units of two types (6 of Type A, 4 of Type B).
What must be done before occupancy:
- Reference the acceptance‑test list in § 120.5 — NA7.5.11 applies to the packaged DX unit and NA7.5.12 applies to the AHU and zone terminal units.
- Packaged DX (NA7.5.11 / MECH‑12A):
- Perform construction inspection to confirm factory‑installed FDD hardware and eligibility items (economizer present, direct‑drive actuators, TXV, refrigerant ports, required sensors).
- Functional tests: create a low‑airflow condition (e.g., obstruct filter) and confirm FDD reports the fault; verify FDD’s refrigerant charge detection; calibrate OA/RA/SA sensors. All checklist items must be “Yes” for PASS.
- AHU & zone terminals (NA7.5.12 / MECH‑13A):
- AHU functional tests: disconnect OA temperature sensor to confirm fault detection; command dampers full open then remove actuator power to confirm fault annunciation at the control workstation; test valve/actuator faults and inappropriate simultaneous heat/cool/economize conditions per test steps.
- Terminal unit sampling: test one of each type (Type A and Type B) and ensure at least 5% of all VAV boxes are tested. With 10 boxes, 5% = 0.5 → code requires testing 1 of each type (that already satisfies the 5% minimum). Run the VAV pressure sensor disconnect and damper‑stuck scenarios on the selected boxes and confirm faults are reported and cleared.
- Documentation and sign‑off: The performing technician must complete the MECH‑12A and MECH‑13A certificate of acceptance forms; if Title 24 Part 1 requires it, a CMATT must perform the acceptance tests and include their certification ID on the form.
Result: If all eligibility items and functional steps pass, the certificates are submitted and the systems are accepted. If eligibility or functional tests fail, the system may still be installed but will not qualify for performance‑path credit and must be documented on the forms.
Related provisions
- § 120.5 — Acceptance tests required (lists NA7.5.11 and NA7.5.12).
- § 120.2(i) — Economizer FDD requirements (sensors, accuracy, status annunciation, reporting options).
- § 120.5(b) — When tests must be performed by a CMATT (certified technician) and documentation rules.
- NA7.5.11 / MECH‑12A (Appendix E / E 805.12) — Packaged DX FDD construction inspection and functional testing procedures.
- NA7.5.12 / MECH‑13A (Appendix E / E 805.13) — AHU and zone terminal FDD functional testing, sampling, and forms.
Code references
Grounded in the retrieved California Energy Code — click a citation to read the verbatim passage:
§ 5.1. High relevance — show source text
(a) Before an occupancy permit is granted, the following equipment and systems shall be certified as meeting the Acceptance Requirements for Code Compliance, as specified by the Reference Nonresidential Appendix NA7. A Certificate of Acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements:
Outdoor air ventilation systems shall be tested in accordance with NA7.5.1.
Constant volume, single zone unitary air conditioning and heat pump unit controls shall be tested in accordance with NA7.5.2.
Duct systems that are subject to testing under Section 120.4(g)1, Section 141.0(b)2Di or Section 141.0(b)2Dii shall be tested in accordance with NA7.5.3.
Air economizers, DOAS, HRV or ERV systems shall be tested in accordance with NA7.5.4. Exception 1 to Section 120.5(a)4: Air economizers installed by the HVAC system manufacturer and certified to the Commission as being factory calibrated and tested are not required to comply with the Functional Testing section of the air economizer controls acceptance test as described in NA7.5.4.2. Exception 2 to Section 120.5(a)4: The DOAS, HRV, or ERV unit that does not meet the exhaust air heat recovery ratio as specified in Section 140.4(q)1 or does not include bypass or control to disable energy recovery as specified in Section 140.4(q)2.
Demand control ventilation systems required by Section 120.1(c)3 shall be tested in accordance with NA7.5.5.
Supply fan variable flow controls shall be tested in accordance with NA7.5.6.
Hydronic system variable flow controls shall be tested in accordance with NA7.5.7 and NA7.5.9.
Boiler or chillers that require isolation controls as specified by Section 140.4(k)2 or 140.4(k)3 shall be tested in accordance with NA7.5.7.
Hydronic systems with supply water temperature reset controls shall be tested in accordance with NA7.5.8.
Automatic demand shed controls shall be tested in accordance with NA7.5.10.
Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units shall be tested in accordance with NA7.5.11.
Automatic fault detection and diagnostics (FDD) for air handling units and zone terminal units shall be tested in accordance with NA7.5.12.
Distributed Energy Storage DX AC Systems shall be tested in accordance with NA7.5.13.
Thermal Energy Storage (TES) Systems shall be tested in accordance with NA7.5.14.
Supply air temperature reset controls shall be tested in accordance with NA7.5.15.
Water-cooled chillers served by cooling towers with condenser water reset controls shall be tested in accordance with NA7.5.16.
When an energy management control system is installed, it shall functionally meet all of the applicable requirements of Part 6.
Occupant sensing zone controls shall be tested in accordance with NA7.5.17.
Conductivity controls and overflow alarms for open and closed-circuit cooling towers shall be tested according to NA7.5.18.
§ 5.6. High relevance — show source text
Supply fan variable flow controls shall be tested in accordance with NA7.5.6.
Hydronic system variable flow controls shall be tested in accordance with NA7.5.7 and NA7.5.9.
Boiler or chillers that require isolation controls as specified by Section 140.4(k)2 or 140.4(k)3 shall be tested in accordance with NA7.5.7.
Hydronic systems with supply water temperature reset controls shall be tested in accordance with NA7.5.8.
Automatic demand shed controls shall be tested in accordance with NA7.5.10.
Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units shall be tested in accordance with NA7.5.11.
Automatic fault detection and diagnostics (FDD) for air handling units and zone terminal units shall be tested in accordance with NA7.5.12.
Distributed Energy Storage DX AC Systems shall be tested in accordance with NA7.5.13.
Thermal Energy Storage (TES) Systems shall be tested in accordance with NA7.5.14.
Supply air temperature reset controls shall be tested in accordance with NA7.5.15.
Water-cooled chillers served by cooling towers with condenser water reset controls shall be tested in accordance with NA7.5.16.
When an energy management control system is installed, it shall functionally meet all of the applicable requirements of Part 6.
Occupant sensing zone controls shall be tested in accordance with NA7.5.17.
Conductivity controls and overflow alarms for open and closed-circuit cooling towers shall be tested according to NA7.5.18.
(b) When certification is required by Title 24, Part 1, Section 10-103.2, the acceptance testing specified by Section 120.5(a) shall be performed by a certified mechanical acceptance test technician (CMATT). If the CMATT is operating as an employee, the CMATT shall
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be employed by a certified mechanical acceptance test employer. The CMATT shall disclose on the certificate of acceptance a valid CMATT certification identification number issued by an approved acceptance test technician certification provider. The CMATT shall complete all certificate of acceptance documentation in accordance with the applicable requirements in Section 10-103(a)4.
Note: Authority cited: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code. Reference: Sections 25007, 25008, 25218.5, 25310, 25402(a)-(b), 25402.1, 25402.4, 25402.5, 25402.8 and 25943, Public Resources Code .
SECTION 120.6—MANDATORY REQUIREMENTS FOR COVERED PROCESSES
Nonresidential and hotel/motel buildings shall comply with the applicable requirements of Sections 120.6(a) through 120.6(k), and the applicable requirements of Sections 110.2(a) and 120.3.
(a) Mandatory requirements for refrigerated warehouses.
§ 805.12.1.2 High relevance — show source text
(1) Compressor enabled
(2) Economizer enabled
(3) Free cooling available
(4) Mixed air low limit cycle active
(5) Heating enabled
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APPENDIX E
The unit controller shall have the capability to manually initiate each operating mode so that the operation of compressors, economizers, fans, and heating system can be independently tested and verified.
E 805.12.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:
Step 1: Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.
Step 2: Verify that the fault detection and diagnostics system reports the fault.
Step 3: Verify that the system is able to verify the correct refrigerant charge.
Step 4: Calibrate outside air, return air, and supply air temperature sensors. E 805.12.2 Acceptance Criteria. The system is able to detect a low airflow condition and report the fault. The system is able to detect where refrigerant charge is low or high and the fault is reported. E 805.13 Automatic Fault Detection Diagnostics (FDD) for Air Handling Units (AHU) and Zone Termi- nal Units (Form MECH-13A). The purpose of this test is to verify that the system detects common faults in air handling units and terminal units. FDD systems for air handling units and zone terminal units require DDC controls to the zone level. Successful completion of this test provides a compliance credit where using the performance approach. An FDD system that does not pass this test shall be permitted to be installed, but no compliance credit will be given. E 805.13.1 Test Procedure. The procedure for performing a functional test for automatic fault detection diagnostics (FDD) for air handling units and zone terminal units shall be in accordance with Section E 805.13.1.1.
E 805.13.1.1 Functional Testing. The functional testing shall be in accordance with Section E 805.13.1.1.1 and Section E 805.13.1.1.2.
E 805.13.1.1.1 Functional Testing for Air Handling Units. The functional testing of AHU with FDD controls shall be in accordance with the following steps:
Step 1: Sensor drift/failure:
(1) Disconnect outside air temperature sensor from unit controller.
(2) Verify that the FDD system reports a fault.
(3) Connect OAT sensor to the unit controller.
(4) Verify that FDD indicates normal system operation.
Step 2: Damper/actuator fault:
(1) From the control system workstation, command the mixing box dampers to full open (100 percent outdoor air).
(2) Disconnect power to the actuator and verify that a fault is reported at the control workstation.
(3) Reconnect power to the actuator and command the mixing box dampers to full open.
(4) Verify that the control system does not report a fault.
(5) From the control system workstation, command the mixing box dampers to a fullclosed position (0 percent outdoor air).
(6) Disconnect power to the actuator and verify that a fault is reported at the control workstation.
§ 160.3 High relevance — show source text
(d) Mechanical acceptance testing.
- Common areas. Before an occupancy permit is granted, the following systems and equipment serving multifamily common areas shall be certified as meeting the Acceptance Requirements for Code Compliance, as specified by Reference Nonresidential Appendix NA7. These systems and equipment shall also comply with the applicable requirements of Section
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160.3(d)3. A Certificate of Acceptance shall be submitted to the enforcement agency that certifies that the equipment and systems meet the acceptance requirements: A. Outdoor air ventilation systems shall be tested in accordance with NA7.5.1. B. Constant volume, single zone air conditioning and heat pump unit controls shall be tested in accordance with NA7.5.2. C. Duct systems shall be tested in accordance with NA7.5.3 where either: a. They are new duct systems; or b. They are part of an altered system. D. Air economizers, DOAS, HRV or ERV systems shall be tested in accordance with NA7.5.4. Exception to Section 160.3(d)1D: Air economizers installed by the HVAC system manufacturer and certified to the Commission as being factory calibrated and tested are not required to comply with the Functional Testing section of the Air Economizer Controls acceptance test as described in NA7.5.4.2. E. Demand control ventilation systems required by Section 160.2(c)3 shall be tested in accordance with NA7.5.5. F. Supply fan variable flow controls shall be tested in accordance with NA7.5.6. G. Hydronic system variable flow controls shall be tested in accordance with NA7.5.7 and NA7.5.9. H. Boilers or chillers that require isolation controls as specified by Section 170.2(c)4Iii or 170.2(c)4Iiii shall be tested in accordance with NA7.5.7.
I. Hydronic systems with supply water temperature reset controls shall be tested in accordance with NA7.5.8.
J. Automatic demand shed controls shall be tested in accordance with NA7.5.10.
K. Fault detection and diagnostics (FDD) for packaged direct expansion units shall be tested in accordance with NA7.5.11. L. Automatic fault detection and diagnostics (FDD) for air handling units and zone terminal units shall be tested in accordance with NA7.5.12.
M. Distributed energy storage DX AC systems shall be tested in accordance with NA7.5.13. N. Thermal energy storage (TES) systems shall be tested in accordance with NA7.5.14. O. Supply air temperature reset controls shall be tested in accordance with NA7.5.15. P. Water-cooled chillers served by cooling towers with condenser water reset controls shall be tested in accordance with NA7.5.16.
Q. When an energy management control system is installed, it shall functionally meet all of the applicable requirements of Part 6.
§ 120.2 High relevance — show source text
Exception to Section 120.2(g): Zones designed to be conditioned continuously.
(h) Automatic demand shed controls. See Section 110.12 for requirements for automatic demand shed controls.
(i) Economizer fault detection and diagnostics (FDD). All newly installed air handlers with a mechanical cooling capacity over 33,000 Btu/hr and an installed air economizer shall include a stand-alone or integrated Fault Detection and Diagnostics (FDD) system in accordance with Subsections 120.2(i)1 through 120.2(i)8.
- The following temperature sensors shall be permanently installed to monitor system operation: outside air, supply air, and when required for differential economizer operation a return air sensor, and
- Temperature sensors shall have an accuracy of ±2°F over the range of 40°F to 80°F; and
- The controller shall have the capability of displaying the value of each sensor; and
- The controller shall provide system status by indicating the following conditions: A. Free cooling available; B. Economizer enabled;
C. Compressor enabled; D. Heating enabled, if the system is capable of heating; and E. Mixed-air low limit cycle active. 5. The unit controller shall allow manual initiation of each operating mode so that the operation of cooling systems, economizers, fans and heating system can be independently tested and verified; and 6. Faults shall be reported in one of the following ways: A. Reported to an Energy Management Control System regularly monitored by facility personnel. B. Annunciated locally on one or more zone thermostats, or a device within five (5) feet of zone thermostat(s), clearly visible, at eye level, and meeting the following requirements: i. On the thermostat, device, or an adjacent written sign, display instructions to contact appropriate building personnel or an HVAC technician; and ii. In buildings with multiple tenants, the annunciation shall either be within property management offices or in a common space accessible by the property or building manager. C. Reported to a fault management application which automatically provides notification of the fault to a remote HVAC service provider. 7. The FDD system shall detect the following faults: A. Air temperature sensor failure/fault; B. Not economizing when it should; C. Economizing when it should not; D. Damper not modulating; and
E. Excess outdoor air.
- The FDD System shall be certified to the Energy Commission as meeting requirements of Subsections 120.2(i)1 through 120.2(i)7 in accordance with Section 110.0 and JA6.3. Exception to Section 120.2(i)8: FDD algorithms based in direct digital control systems are not required to be certified to the Energy Commission.
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(j) Direct Digital Controls (DDC) . Direct Digital Controls to the zone shall be provided as specified by Table 120.2-A. The provided DDC system shall meet the control logic requirements of Sections 120.1(d), 110.12(a) and 110.12(b), and be capable of the following:
The provided DDC system shall meet the control logic requirements of Sections 110.12(a), 110.12(b) and 120.1(d) and be capable of the following:
- Monitoring zone and system demand for fan pressure, pump pressure, heating and cooling;
§ 110.12 High relevance — show source text
** See Section 110.12 for requirements for automatic demand shed controls. H. Economizer fault detection and diagnostics (FDD). All newly installed air handlers with a mechanical cooling capacity over 33,000 Btu/hr and an installed air economizer shall include a stand-alone or integrated fault detection and diagnostics (FDD) system in accordance with Subsections 160.3(a)2Hi through 160.3(a)2Hviii. i. The following temperature sensors shall be permanently installed to monitor system operation: outside air, supply air and, when required for differential economizer operation, a return air sensor; and ii. Temperature sensors shall have an accuracy of ±2°F over the range of 40°F to 80°F; and iii. The controller shall have the capability of displaying the value of each sensor; and iv. The controller shall provide system status by indicating the following conditions: a. Free cooling available; b. Economizer enabled;
c. Compressor enabled; d. Heating enabled, if the system is capable of heating; and e. Mixed air low limit cycle active. v. The unit controller shall allow manual initiation of each operating mode so that the operation of cooling systems, economizers, fans and heating systems can be independently tested and verified; and vi. Faults shall be reported in one of the following ways: a. Reported to an energy management control system regularly monitored by facility personnel. b. Annunciated locally on one or more zone thermostats, or a device within 5 feet of zone thermostat(s), clearly visible, at eye level and meeting the following requirements:
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I. On the thermostat, the device or an adjacent written sign, display instructions to contact appropriate building personnel or an HVAC technician; and II. In buildings with multiple tenants, the annunciation shall either be within property management offices or in a common space accessible by the property or building manager. c. Reported to a fault management application that automatically provides notification of the fault to remote HVAC service provider. vii. The FDD system shall detect the following faults: a. Air temperature sensor failure/fault; b. Not economizing when it should; c. Economizing when it should not; d. Damper not modulating; and
e. Excess outdoor air.
viii. The FDD system shall be certified to the Energy Commission as meeting the requirements of Sections 160.3(a)2Hi through 160.3(a)2Hvii in accordance with Section 110.0 and JA6.3. Exception to Section 160.3(a)2Hviii: FDD algorithms based in direct digital control systems are not required to be certified to the Energy Commission. I. Direct digital controls (DDC). Direct digital controls to the zone shall be provided as specified by Table 160.3-C. i. The provided DDC system shall meet the control logic requirements of Sections 160.3(a)2E and 160.3(a)2G, and be capable of the following: ii. Monitoring zone and system demand for fan pressure, pump pressure, heating and cooling; iii. Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers; iv. Automatically detecting the zones and systems that may be excessively driving the reset logic and generate an alarm or other indication to the system operator; v. Readily allow operator removal of zone(s) from the reset algorithm; vi.
§ 805.11.2 High relevance — show source text
Step 1: Engage the global demand shed system. Verify and document the following:
(1) That the cooling setpoint in noncritical spaces increases by the proper amount.
(2) That the cooling setpoint in critical spaces do not change.
Step 2: Disengage the global demand shed system. Verify and document the following:
(1) That the cooling setpoint in noncritical spaces return to their original values.
(2) That the cooling setpoint in critical spaces do not change.
E 805.11.2 Acceptance Criteria. The control system changes the setpoints of noncritical zones on activation of a single central hardware or software point then restores the initial setpoints where the point is released.
E 805.12 Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion (DX) Units (Form MECH-12A). The purpose of this test is to verify proper fault detection and reporting for automated fault detection and diagnostics systems for packaged units. Automated FDD systems ensure proper equipment operation by identifying and diagnosing common equipment problems such as improper refrigerant charge, low airflow, or faulty economizer operation. Qualifying FDD systems receive a compliance credit where using the performance approach. A system that does not meet the eligibility requirements shall be permitted to be installed, but no compliance credit will be given.
E 805.12.1 Test Procedure. The procedure for performing a functional test for fault detection and diagnostics (FDD) for packaged direct-expansion (DX) units shall be in accordance with Section E 805.12.1.1 and
Section E 805.12.1.2.
E 805.12.1.1 Construction Inspection. Prior to functional testing, verify and document that the FDD
hardware is installed on equipment by the manufacturer, and that equipment make and model include factory-installed FDD hardware that match the information indicated on copies of the manufacturer’s cut sheets and on the plans and specifications.
This procedure applies to fault detection and diagnostics (FDD) system for direct-expansion packaged units containing the following features:
(1) The unit shall include a factory-installed economizer and shall limit the economizer dead band to not more than 2°F (-17°C).
(2) The unit shall include direct-drive actuators on outside air and return air dampers.
(3) The unit shall include an integrated economizer with either differential dry-bulb or differential enthalpy control.
(4) The unit shall include a low temperature lockout on the compressor to prevent coil freeze-up or comfort problems.
(5) Outside air and return air dampers shall have maximum leakage rates in accordance to this appendix.
(6) The unit shall have an adjustable expansion control device such as a thermostatic expansion valve (TXV).
(7) To improve the ability to troubleshoot charge and compressor operation, a high-pressure refrigerant port will be located on the liquid line. A low-pressure refrigerant port will be located on the suction line.
(8) The following sensors shall be permanently installed to monitor system operation, and the controller shall have the capability of displaying the value of each parameter:
(a) Refrigerant suction pressure
(b) Refrigerant suction temperature
(c) Liquid line pressure
(d) Liquid line temperature
(e) Outside air temperature
(f) Outside air relative humidity
(g) Return air temperature
(h) Return air relative humidity
(i) Supply air temperature
(j) Supply air relative humidity
§ 503.3. High relevance — show source text
Exception : DDC is not required for systems using the simplified approach to compliance in accordance with Section E 503.3. [ASHRAE 90.1:6.4.3.10.1]
E 503.4.6.12.2 DDC Controls. Where DDC is required by Section E 503.4.6.12.1, the DDC
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APPENDIX E
system shall be capable of and configured with all of the following, as required, to provide the control logic required in Section E 503.5:
(1) Monitoring zone and system demand for fan pressure, pump pressure, heating, and cooling.
(2) Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers.
(3) Automatically detecting those zones and systems that are capable of excessively driving the reset logic and generate an alarm or other indication to the system operator.
(4) Readily allowing operator removal of zone(s) from the reset algorithm. [ASHRAE 90.1:6.4.3.10.2]
E 503.4.6.12.3 DDC Display. Where DDC is required in accordance with Section E 503.4.6.12.1 for new buildings, the DDC system shall be capable of trending and graphically displaying input and output points. [ASHRAE 90.1:6.4.3.10.3]
E 503.4.6.13 Economizer Fault Detection and Diagnostics (FDD). Air-cooled direct-expansion cooling units listed in Tables E 503.7.1(1) and E 503.7.1(2), where an air economizer is installed in accordance with Section E 503.5, shall include a fault detection and diagnostics (FDD) system complying with the following:
(1) The following temperature sensors shall be permanently installed to monitor system operation:
(a) Outdoor air
(b) Supply air
(c) Return air, where required for economizer control
(2) The system shall have the capability of displaying the value of each sensor.
(3) The FDD system or unit controls shall be capable of and configured to provide system status by indicating the following:
(a) Free cooling available
(b) Economizer enabled
(c) Compressor enabled
(d) Heating enabled
(e) Mixed-air low-limit cycle active
(4) The FDD system or unit controls shall have provisions to manually initiate each operating mode so that the operation of compressors, economizers, fans, and the heating system can be independently tested and verified.
(5) The FDD system shall be capable of and configured to detect the following faults:
(a) Air temperature sensor failure/fault
(b) Not economizing when the unit should be economizing
(c) Economizing when the unit should not be economizing
(d) Damper not modulating
(e) Excess outdoor air
(6) The FDD system shall be capable of and configured to report faults to a fault management appli
TABLE E 503.4.6.12.1
DDC APPLICATIONS AND QUALIFICATIONS
[ASHRAE 90.1:6.4.3.10.1]
§ 805.10.2 High relevance — show source text
(3) System operation shall stabilize within 5 minutes after test procedures are initiated.
Step 2: Modulate control valves to reduce water flow to 50 percent of the design flow or less, but not lower than the pump minimum flow. Verify and document the following:
(1) Pump speed decrease.
(2) Current operating setpoint has decreased (for systems with DDC to the zone level).
(3) Current operating setpoint has not increased (for all other systems).
(4) System pressure is within 5 percent of current operating setpoint.
(5) System operation stabilizes within 5 minutes after test procedures are initiated.
2025 CALIFORNIA MECHANICAL CODE 487
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX E
E 805.10.2 Acceptance Criteria. The differential pressure sensor is either factory calibrated (with calibration certificates) or field calibrated. The pressure sensor shall be located at or near the most remote HX or control valve. The setpoint system controls shall stabilize.
E 805.11 Automatic Demand Shed Control (Form MECH-11A). The purpose of this test is to ensure that the central demand shed sequences have been properly programmed into the DDC system.
E 805.11.1 Test Procedure. The procedure for performing a functional test for automatic demand shed controls shall be in accordance with Section E 805.11.1.1
and Section E 805.11.1.2.
E 805.11.1.1 Construction Inspection. Prior to functional testing, verify and document that the EMCS interface enables activation of the central
demand shed controls.
E 805.11.1.2 Functional Testing. The functional testing shall comply with the following steps:
Step 1: Engage the global demand shed system. Verify and document the following:
(1) That the cooling setpoint in noncritical spaces increases by the proper amount.
(2) That the cooling setpoint in critical spaces do not change.
Step 2: Disengage the global demand shed system. Verify and document the following:
(1) That the cooling setpoint in noncritical spaces return to their original values.
(2) That the cooling setpoint in critical spaces do not change.
E 805.11.2 Acceptance Criteria. The control system changes the setpoints of noncritical zones on activation of a single central hardware or software point then restores the initial setpoints where the point is released.
E 805.12 Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion (DX) Units (Form MECH-12A). The purpose of this test is to verify proper fault detection and reporting for automated fault detection and diagnostics systems for packaged units. Automated FDD systems ensure proper equipment operation by identifying and diagnosing common equipment problems such as improper refrigerant charge, low airflow, or faulty economizer operation. Qualifying FDD systems receive a compliance credit where using the performance approach. A system that does not meet the eligibility requirements shall be permitted to be installed, but no compliance credit will be given.
E 805.12.1 Test Procedure. The procedure for performing a functional test for fault detection and diagnostics (FDD) for packaged direct-expansion (DX) units shall be in accordance with Section E 805.12.1.1 and
Section E 805.12.1.2.
§ 805.12.1.2 High relevance — show source text
hardware is installed on equipment by the manufacturer, and that equipment make and model include factory-installed FDD hardware that match the information indicated on copies of the manufacturer’s cut sheets and on the plans and specifications.
This procedure applies to fault detection and diagnostics (FDD) system for direct-expansion packaged units containing the following features:
(1) The unit shall include a factory-installed economizer and shall limit the economizer dead band to not more than 2°F (-17°C).
(2) The unit shall include direct-drive actuators on outside air and return air dampers.
(3) The unit shall include an integrated economizer with either differential dry-bulb or differential enthalpy control.
(4) The unit shall include a low temperature lockout on the compressor to prevent coil freeze-up or comfort problems.
(5) Outside air and return air dampers shall have maximum leakage rates in accordance to this appendix.
(6) The unit shall have an adjustable expansion control device such as a thermostatic expansion valve (TXV).
(7) To improve the ability to troubleshoot charge and compressor operation, a high-pressure refrigerant port will be located on the liquid line. A low-pressure refrigerant port will be located on the suction line.
(8) The following sensors shall be permanently installed to monitor system operation, and the controller shall have the capability of displaying the value of each parameter:
(a) Refrigerant suction pressure
(b) Refrigerant suction temperature
(c) Liquid line pressure
(d) Liquid line temperature
(e) Outside air temperature
(f) Outside air relative humidity
(g) Return air temperature
(h) Return air relative humidity
(i) Supply air temperature
(j) Supply air relative humidity
The controller will provide system status by indicating the following conditions:
(1) Compressor enabled
(2) Economizer enabled
(3) Free cooling available
(4) Mixed air low limit cycle active
(5) Heating enabled
488 2025 CALIFORNIA MECHANICAL CODE
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX E
The unit controller shall have the capability to manually initiate each operating mode so that the operation of compressors, economizers, fans, and heating system can be independently tested and verified.
E 805.12.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:
Step 1: Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.
Step 2: Verify that the fault detection and diagnostics system reports the fault.
Step 3: Verify that the system is able to verify the correct refrigerant charge.
Step 4: Calibrate outside air, return air, and supply air temperature sensors. E 805.12.2 Acceptance Criteria. The system is able to detect a low airflow condition and report the fault. The system is able to detect where refrigerant charge is low or high and the fault is reported. E 805.13 Automatic Fault Detection Diagnostics (FDD) for Air Handling Units (AHU) and Zone Termi- nal Units (Form MECH-13A). The purpose of this test is to verify that the system detects common faults in air handling units and terminal units. FDD systems for air handling units and zone terminal units require DDC controls to the zone level. Successful completion of this test provides a compliance credit where using the performance approach.
§ 120.2 High relevance — show source text
Exception 3 to Sections 120.2(e) 1 and 2: Systems serving hotel/motel guest rooms, if they have a readily accessible manual shut-off switch.
2025 CALIFORNIA ENERGY CODE 73
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS
- Hotel and motel guest rooms shall have captive card key controls, occupancy sensing controls or automatic controls such that, no longer than 30 minutes after the guest room has been vacated, setpoints are set up at least +5°F (+3°C) in cooling mode and set down at least -5°F (-3°C) in heating mode.
Exception to Section 120.2(e): Systems serving healthcare facilities.
(f) Dampers for air supply and exhaust equipment. Outdoor air supply and exhaust equipment shall be installed with dampers that automatically close upon fan shutdown.
Exception 1 to Section 120.2(f): Equipment that serves an area that must operate continuously.
Exception 2 to Section 120.2(f): Gravity and other nonelectrical equipment that has readily accessible manual damper controls.
Exception 3 to Section 120.2(f): At combustion air intakes and shaft vents.
Exception 4 to Section 120.2(f): Where prohibited by other provisions of law.
(g) Isolation area devices. Each space-conditioning system serving multiple zones with a combined conditioned floor area of more than 25,000 square feet shall be designed, installed and controlled to serve isolation areas.
- Each zone, or any combination of zones not exceeding 25,000 square feet, shall be a separate isolation area.
- Each isolation area shall be provided with isolation devices, such as valves or dampers, that allow the supply of heating or cooling to be reduced or shut off independently of other isolation areas.
- Each isolation area shall be controlled by a device meeting the requirements of Section 120.2(e)1.
Exception to Section 120.2(g): Zones designed to be conditioned continuously.
(h) Automatic demand shed controls. See Section 110.12 for requirements for automatic demand shed controls.
(i) Economizer fault detection and diagnostics (FDD). All newly installed air handlers with a mechanical cooling capacity over 33,000 Btu/hr and an installed air economizer shall include a stand-alone or integrated Fault Detection and Diagnostics (FDD) system in accordance with Subsections 120.2(i)1 through 120.2(i)8.
- The following temperature sensors shall be permanently installed to monitor system operation: outside air, supply air, and when required for differential economizer operation a return air sensor, and
- Temperature sensors shall have an accuracy of ±2°F over the range of 40°F to 80°F; and
- The controller shall have the capability of displaying the value of each sensor; and
- The controller shall provide system status by indicating the following conditions: A. Free cooling available; B. Economizer enabled;
C. Compressor enabled; D. Heating enabled, if the system is capable of heating; and E. Mixed-air low limit cycle active. 5. The unit controller shall allow manual initiation of each operating mode so that the operation of cooling systems, economizers, fans and heating system can be independently tested and verified; and 6. Faults shall be reported in one of the following ways: A. Reported to an Energy Management Control System regularly monitored by facility personnel.
CMC § 2025 High relevance — show source text
Reconnect power to the actuator and command the dampers closed.|Y / N
| |
h.
Verify that the control system does not report a fault during normal operation.|Y / N| |Step 3: Valve/actuator fault.
|Step 3: Valve/actuator fault.
| |
a.
From the control system workstation, command the heating and cooling coil valves to full open or
closed, then disconnect power to the actuator and verify that a fault is reported at the control workstation.|Y / N| |
Step 4: Inappropriate simultaneous heating, mechanical cooling, and/or economizing.
|
Step 4: Inappropriate simultaneous heating, mechanical cooling, and/or economizing.
| |
a.
From the control system workstation, override the heating coil valve and verify that a fault is
reported at the control workstation.|Y / N
| |
b.
From the control system workstation, override the cooling coil valve and verify that a fault is
reported at the control workstation.|Y / N
| |
c.
From the control system workstation, override the mixing box dampers and verify that a fault is
reported at the control workstation.|Y / N|2025 CALIFORNIA MECHANICAL CODE 523
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX E
CERTIFICATE OF ACCEPTANCE MECH-13A Col2
Automatic Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units and Zone
(Page 3 of 4)
Terminal Units Acceptance
Automatic Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units and Zone
(Page 3 of 4)
Terminal Units Acceptance
Project Name/Address:
Project Name/Address:
System Name or Identification/Tag:System Location or Area Served: B. Functional Testing for Zone Terminal Units. Results
Testing shall be performed on one of each type of terminal unit (VAV box) in the project. A
minimum of 5% of results the terminal boxes shall be tested.
Testing shall be performed on one of each type of terminal unit (VAV box) in the project. A
**minimum of 5% of results the terminal boxes shall be tested.
Frequently asked questions
Who must perform the FDD acceptance tests?
When Title 24, Part 1 Section 10‑103.2 requires certification, a Certified Mechanical Acceptance Test Technician (CMATT) must perform the tests and include their CMATT ID on the Certificate of Acceptance. § 120.5(b)
If an FDD system fails the functional test, can it still be installed?
Yes. The code permits installation of an FDD system that does not pass the eligibility or functional checks, but it will not receive performance‑path compliance credit. See NA7.5.11 / MECH‑12A and related notes.
What sampling rule applies to VAV boxes?
Test one of each terminal‑unit type and a minimum of 5% of all terminal units in the project (whichever provides representative coverage). This is in NA7.5.12 (MECH‑13A).
Are DDC‑based FDD algorithms required to be certified to the Energy Commission?
No — DDC‑based FDD algorithms are excepted from the Energy Commission certification requirement, but they remain subject to the NA7 functional acceptance tests.
What faults must economizer FDD detect?
Economizer FDD must detect air temperature sensor failure, not economizing when it should, economizing when it should not, damper not modulating, and excess outdoor air; controllers must show status and allow manual initiation of modes. § 120.2(i) and NA7 references.
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