C403.2.4.7 Economizer Fault Detection and Diagnostics (FDD)

Air-cooled unitary direct-expansion units listed in Tables C403.2.3(1) through C403.2.3(3) and variable refrigerant flow (VRF) units that are equipped with an economizer in accordance with Section C403.3 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:

   1. 1.1. Outside air.
   2. 1.2. Supply air.
   3. 1.3. Return air.
2. Temperature sensors shall have an accuracy of ±2°F (1.1°C) over the range of 40°F to 80°F (4°C to 26.7°C).
3. Refrigerant pressure sensors, where used, shall have an accuracy of ±3 percent of full scale.

4. The unit controller shall be capable of providing system status by indicating the following:

   1. 4.1. Free cooling available.
   2. 4.2. Economizer enabled.
   3. 4.3. Compressor enabled.
   4. 4.4. Heating enabled.
   5. 4.5. Mixed air low limit cycle active.
   6. 4.6. The current value of each sensor.
5. The unit controller shall be capable of manually initiating each operating mode so that the operation of compressors, economizers, fans and the heating system can be independently tested and verified.
6. The unit shall be capable of reporting faults to a fault management application accessible by dayto-day operating or service personnel, or annunciated locally on zone thermostats.

7. The FDD system shall be capable of detecting the following faults:

   1. 7.1. Air temperature sensor failure/fault.
   2. 7.2. Not economizing when the unit should be economizing.
   3. 7.3. Economizing when the unit should not be economizing.
   4. 7.4. Damper not modulating.
   5. 7.5. Excess outdoor air.