York Heat Pump: Yorkguard VI

Re: Low Discharge Temperature (Cooling)

The status lights on the module will indicate as follows: Red = On, Green = 6 Flash.

• 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.