York Heat Pump: YZF 

Re: High Pressure Lockout - Last Mode Heat Pump (Cooling)

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.

CHECKOUT:

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

• 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
  • SWITCH METER LEADS BACK TO "COM" AND "V" BEFORE PROCEEDING!
• 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 (at the ODF terminal of the Yorkguard board).
    • 230v Power + No Motor Operation = Bad Motor or Capacitor
    • 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)

• 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 psig + Normal Suction psig = Overcharged
    • Sub-Cooling > 13 deg. + High Discharge psig + Low Suction psig = Bad Indoor Expansion Valve
    • Sub-Cooling < 2 deg. + High Discharge psig + Hot Liquid Line = Low Outdoor Heat Transfer (Airflow).