Heat Pump - Low Pressure Fault - Heating

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.

CHECKOUT:

1. Check Unit Operation

• Make sure the thermostat is set correctly and calling for Heat.
• Allow up to 5 minutes for compressor to start.
  • Outdoor Unit Operating →  Step 2. Check Refrigerant Pressures
• 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 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