CADM Fault Code 3

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This installation was on a 4-story home, and the tech had not yet gone to the basement to troubleshoot the “infinity” water source heat pump, as he was told he by the homeowner. He was in the attic at the infinity furnace above the 4th floor. He was getting his dcv in the proper range on his A and B green plug on the air handler, 3 to 4 vdc. His indoor board ohm reading was in range, 28k to 32 k. The tech ohmed out the A and B thermostat wires on the water source heat pump from the upstairs. His ohm reading was not in range of a normal infinity board. His reading was around 64.4k. The tech then made the long walk to the basement where the “geothermal heat pump” was located. Bingo.

Blue circuit board with many wires and components inside an electronic device casing

Close-up of a blue circuit board with green terminal block, resistor rows, and connected wires.

Wiring harness and colored connectors inside an electrical control panel with a cooling fan.

Circuit wiring diagram label on a black machine, with a screwdriver pointing at the main board.

If you see a fixed negative or a small amount of fluctuating volts staying in the negative, the indoor board has failed.

If you see a fixed positive volt reading or a fluctuating positive reading the outdoor board is bad.

The reactor also needs to be checked. Check the reactor with the wires off and ohm it out. The ohm reading should be .1-1 ohm and should not be grounded.

What is fault code 3 on the Comfort Alert Diagnostic Module (CADM) and why am I getting nuisance trips?

CADM Fault code 3 is a short cycle alarm and lock out meaning the system did not run for a minimum of 3 minutes. This could be due to a no load or low load application, like a church. When no one is occupying the building, the system ran in cooling mode for under 3 minutes then cycled off. This has to happen four consecutive times, then the CADM will lock out on fault code 3. To reset the fault you simply power cycle the outdoor unit.

If you are receiving a code 3 and it is not from a lack of run time, then you need to look into a possible charge problem or blower problem.

This information can be located in the installation manual that comes with the unit. This is the definition from the install manual:

Yellow “ALERT” Flash Code 3 Short Cycling Compressor is running only briefly (four consecutive cycles of less than three minutes each) LOCKOUT 1. If low pressure switch is open: a. Low refrigerant charge b. Evaporator blower is not running c. Evaporator coil is frozen d. Faulty metering device e. Condenser coil is dirty f. Liquid line restriction (filter drier blocked if present) 2. If high-pressure switch is open, go to Flash Code 2 information 3. Intermittent thermostat demand signal four. System or control board defective.

The system needs a minimum run time for oil return. The way we fix this is with the correct type of thermostat.

I recommend two different thermostats for this application to help resolve fault code 3 due to short cycle.

Carrier Part Numbers 33CS2PPRH-03 and 33CS2PP2S-03 commercial thermostats with built in 3 minute minimum on time.
PRO1 T855 is a commercial programmable thermostat. You have to enable this feature and I recommend setting to a minimum of 5 minutes.

By using one of these thermostats, with a minimum on or run time, fault code 3 short cycle problem will go away.