If, after energizing the compressor contactor for 1 hour, the Yorkguard module senses a compressor discharge temperature lower than 90 deg. the unit will enter a Low Discharge Temperature lockout which disables compressor operation.
This code is intended to indicate a compressor not operating, but other issues that may result in a low compressor discharge reading are often the cause.

CHECKOUT:

1. Check Outdoor Unit

Make sure the thermostat is set correctly and calling for Cool.
Remove the access panel of the outdoor unit.
- Unit Operating → Step 4. Check Pressures & Temperature
Check for 230V inlet power on the compressor contactor.
- No Power → Step 2. Check Breaker & Compressor
- Power Present --> Check Diagnostic Light on Board
  - Diagnostic Present --> Reset by removing "R" and "Y" from the board.

2. Check Breaker & Compressor

Pull the service disconnect switch.
Check resistance between each leaving leg of the compressor contactor & ground.
- Any resistance = Electrical Short --> Check Compressor
- No Short --> Check Capacitor
Check the unit breaker at the breaker panel and reset if necessary.
Re-insert the service disconnect plug to restore power to the outdoor unit.
Re-check for 230V on the contactor inlet.
- No Power --> Loose or Burnt Wires in Disconnect or Bad Breaker
- Unit comes on and operates normally --> Step 4. Check Pressures & Temperatures

3. Check Contactor

Contactor pulled-in but no compressor operation:
- Check for 230V across the leaving legs of the compressor contactor.
  - Inlet Power + No (or low) Outlet Power = Bad Contactor
  - Inlet Power + Outlet Power + No Compressor = Compressor off on Internal Overload or Burnt Compressor Terminals

4. Check Pressures & Temperatures

Turn off power to the outdoor unit by pulling the service disconnect or turning off the breaker.
Hook-up refrigerant gauges to the pressure ports on the unit.
- Blue --> "True Suction" Low Pressure
- Red --> High Pressure (liquid line)
Re-apply power to the outdoor unit.
Start the compressor with a call for cooling from the thermostat.
Allow the system to operate for at least 5 - 10 minutes.
Observe refrigerant pressures.
- Normal R-22 Pressures = 55 to 80 psig Suction, 150 to 270 psig Head.
- Normal R410A Pressures = 100 to 150 psig Suction, 200 to 400 psig Head.
Hook an insulated thermistor to the compressor discharge line and check temperature.
- Normal discharge temperature = 130 to 160 deg.
  - Discharge Temperature Below 100 deg. --> Contact Supervisor

5. Check Discharge Sensor

Pull the service disconnect switch.
Remove the discharge sensor wires from the board.
Set the mulit-meter for 200K Ohms.
Check the resistance across the sensor (see York Sensor Resistance Chart).
Compare the sensor temperature to the actual compressor discharge temperature.
- Replace sensor if necessary.

► If necessary, you can disable the discharge temperature sensor and the associated fault codes. (Confirm with Supervisor first.)

Power off the Yorkguard VI by disconnecting the "R" wire.
Disconnect the two discharge sensor wires from the Yorkguard board (tape-off the ends).
Re-power the board by re-connecting the "R" wire.