Yorkguard VI - High Pressure Lockout - Cooling

Article ID: 274
Last updated: 7 Jun, 2021

York Heat Pump: Cooling

Re: High Pressure Lockout - Last Mode Heat Pump

The heat pump was running in cooling mode and the high pressure switch tripped.

A High Pressure Lockout is indicated by the following LED pattern on the outdoor unit control board:

  • Green = Off
  • Red = 2 Flashes

X/L Output

  • 2 Flashes at Thermostat = Soft Lockout
    • Switch opened two times in 6 hours.
    • Reset by cycling thermostat or jumping Test pins.
  • 3 Flashes at Thermostat = Hard Lockout
    • Four Soft Lockouts in 12 hours.
    • Reset by cycling 24VAC power to the board.

Qty Possible Causes:
Bad Condenser Motor / Capacitor
Refrigerant Over-Charge
Bad I/D Expansion Valve
Low Outdoor Airflow
Refrigerant Restriction
Bad Pressure Switch


1. Check Unit Operation

  • Set the thermostat to call for cooling.
    • If the heat pump is in lockout (flashing a code) ⇒ Reset by removing 24VAC power to the outdoor control board (Remove "R" or cycle power to the air handler).
    • Allow 5 minutes for the anti-short-cycle delay or jump the Test pins to bypass the timer.
  • Observe the outdoor unit to ensure that the compressor and condenser fan motor start.
    • Unit Starts and Runs Normally → Step 3. Check Refrigerant Pressures
    • Unit Doesn't Start ⇒ Check Control Board Diagnostic Light
      • Flashing a Fault Code = Still Locked-Out
        • Reset by removing and reconnecting "R" and "Y" at the o/d unit control board for at least 5 seconds.
    • If the control board re-enters Code 2 without starting the compressor = Bad Pressure Switch

2. Check O/D Motor & Capacitor

  • The YZH unit has an ECM outdoor fan motor, the YZE has a standard PSC motor with a capacitor.
  • YZE
  • Check Capacitor
    • Turn off power to the unit by pulling the service disconnect or by turning the breaker off.
      • Use a multi-meter to confirm that voltage is not present.
    • Remove the capacitor wires (short terminals before touching).
    • Move Multi-Meter leads to COM and MFD.
    • Set Meter to 200 MFD.
    • At the capacitor, place one meter lead on "C" or "Com" and the other meter lead on "Fan".
    • Confirm MFD reading with capacitor rating.
      • Less than 80% of rating = Bad Capacitor
  • Check Motor
    • Re-apply power to the heat pump.
    • Set the thermostat to call for cool.
    • When the compressor contactor energizes, check for 230V to the motor between "C" or "COM" at the capacitor and the Black motor wire.
      • Power + No Motor Operation = Bad Motor or Capacitor
      • No Power = Bad Control Board 
  • YZH
  • Re-apply power to the heat pump.
  • Set the thermostat to call for cool.
  • When the compressor contactor energizes, check for 24V to the motor module between the Blue wire on the contactor coil and the Yellow wire on "ODF" at the control board.
    • Power + No Motor Operation = Bad Motor/Module
    • No Power = Bad Control Board 

3. Check Refrigerant Pressures

  • Initiate a call for heat from the thermostat.
  • Hook-up refrigerant gauges to the pressure ports on the unit.
    • Blue ⇔ "True Suction" Low Pressure
    • Red ⇔ High Pressure (liquid refrigerant line)

Normal Pressure Range: Cooling
Refrigerant 55-70 Deg O/D 75-100 Deg O/D
  • 110-130 Suction
  • 250-300 Discharge
  • 125-150 Suction
  • 270-400 Discharge
  • Place an insulated temperature probe on the liquid line near the outdoor unit.
  • Allow the unit to run for at least 10 minutes.
  • Monitor pressures and temperature as the system operates.
    • If pressure exceeds Normal Range or kicks-off on Hi Pressure safety in the first 5 minutes = Bad Overcharge or No Outdoor Airflow 
    • If the compressor never kicks on & the control locks-out on Hi Pressure ⇒ Suspect a Bad Pressure Switch

4. Check Sub-Cooling

  • Record "Saturation Temperature" from the discharge pressure gauge.
  • Subtract the Actual liquid line temperature reading.
    • Saturation Temp - Liquid Line Temp = Sub-Cooling
      • Sub-Cooling > 13 deg. + High Discharge + High Suction = Overcharged
      • Sub-Cooling > 13 deg. + High Discharge + Low Suction = Bad Indoor Expansion Valve
      • Sub-Cooling < 2 deg. + High Discharge = Low Outdoor Heat Transfer (Airflow).

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Article ID: 274
Last updated: 7 Jun, 2021
Revision: 11
Access: Public
Views: 877
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