Heat Pump: YorkGuard VI
Re: Low Pressure Fault - Heating
These heat pumps are equipped with a YorkGuard VI module which monitors and controls unit operation and defrost.
A Low Pressure Fault is indicated by the following LED pattern on the outdoor unit control board:
- Green = Off
- Red = 4 Flashes
Low Pressure Switch
- The heat pump is equipped with a low-pressure switch which is connected to the control at the LPS terminals.
- If the low-pressure switch opens for more than five seconds, the control will cause a soft lockout condition and display the appropriate fault codes.
- The control will ignore the low pressure switch input and not cause a soft lockout condition if it opens during the following conditions.
- Defrost operation
- First two minutes of compressor operation
- Two minutes following the completion of a defrost cycle
- TEST input shorted with Y1 input energized
► Unlike previous models, the YorkGuard VI does not flash the actual diagnostic code at the thermostat, only a code 2, 3 or 4 to indicate a "Soft" or "Hard" lockout.
||Bad Heating Expansion Valve
||Low Refrigerant Charge
||Bad Pressure Switch
||Refrigerant Flow Restriction
1. Check Unit Operation
- Make sure the thermostat is set correctly and calling for Heat.
- Allow up to 5 minutes for compressor to start.
- Remove the access panel of the outdoor unit.
- Check the Diagnostic Indication Lights.
- Unit still in Lockout ⇒ Remove 24VAC power to the board by removing the Red wire from the "R" terminal. Re-apply power after several seconds.
2. Check Refrigerant Pressures
- Hook-up refrigerant gauges to the pressure ports on the unit.
- Blue --> "True Suction" Low Pressure
- Red --> High Pressure (either refrigerant line)
- Ensure that the unit is running at full capacity (Red and Green LEDs both on).
- Monitor pressures as the system operates.
|Normal Pressure Range
||0-30 Deg O/D
||30-50 Deg O/D
- 75-100 Suction
- 250-320 Discharge
- 100-150 Suction
- 250-375 Discharge
- Normal Pressures + Low Pressure Lockout = Bad Pressure Switch
Low Pressure Issues
- If a Liquid-Line Sight Glass is installed, observe for bubbles in the sight glass (after the system has been operating for at least 5 min.)
- Low Suction + Low Discharge + Bubbles in Sight Glass + Expansion Valve Frosting = Low Refrigerant Charge
- Try adding refrigerant through the Low Pressure gauge.
- Suction and Discharge Pressures should gradually increase as refrigerant is added.
- If the Discharge Pressure increases but the Suction stays low or drops = Bad Expansion Valve
- Low Suction + Low Discharge + Clear Sight Glass + Expansion Valve Frosting = Bad Expansion Valve