York Heat Pump: YZT

Re: High Pressure Lockout - Heating Mode

The heat pump was running in normal heat mode (not in defrost) and the high pressure switch tripped.

There are three levels of High Pressure fault:

• LED = On, 7-Segment = "0 1" ⇔ High Pressure Fault (No Lockout)
• LED = 2 Flashes, 7-Segment = "0 2" ⇔ 2 High Pressure Trips in 6 Hours (Soft Lockout)
• LED = 3 Flashes, 7-Segment = "0 2" ⇔ 4 High Pressure Trips in 12 Hours (Hard Lockout)

CHECKOUT:

1. Check Indoor Airflow

• Set the thermostat to call for heat.
• Confirm that the indoor fan is operating and air is blowing out of the supply registers
  • No Airflow → Step 2. Check Blower Motor
  • Airflow → Step 3. Check Refrigerant Pressures

2. Check Blower Motor

• At the air handler, confirm that 24VAC is present between "C" and "G", "Y1" or "Y2".
  • No 24VAC power = No signal from thermostat
• Confirm that 240VAC is being supplied to the motor.
  • 240V Power Present + No Blower Operation = Bad Blower Motor 

3. Check Refrigerant Pressures

• If the heat pump is in lockout, reset by removing 24VAC power from the outdoor control board.
• Hook-up refrigerant gauges to the pressure ports on the unit.
  • Blue ⇒ "True Suction" Low Pressure (NOT THE SUCTION LINE)
  • Red ⇒ High Pressure (small liquid line)
• Place an insulated temperature probe on the liquid line near the outdoor unit.
• Initiate a call for heat from the thermostat (bypass Anti-Short-Cycle timer by pressing the PUSH BUTTON for 2-6 seconds).
• Ensure that the unit is operating in 2nd Stage Compressor.
• Allow the unit to run for at least 10 minutes.
• Monitor pressures and temperature as the system operates.

• If pressure exceeds Normal Range and kicks-off on Hi Pressure safety in the first 5 minutes = Bad Overcharge or No Indoor Blower
• 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 Pressure + Normal Suction Pressure = Overcharged
    • Sub-Cooling > 13 deg. + High Discharge Pressure + Low Suction Pressure = Bad O/D Expansion Valve
    • Sub-Cooling < 2 deg. + High Discharge Pressure + Hot Liquid Line = Low Indoor Heat Transfer (Airflow) → Step 5. Check Heat Pump Temperature Rise

5. Check Heat Pump Temperature Rise

• Check to make sure the indoor fan is operating.
• Disconnect auxiliary heat (remove "W" at the air handler or thermostat).
• Check the Return Air Temperature at the air handler (at the filter if possible).
  • High Return Air Temperature (more than 85 deg.) = Heat Recycling
• Check the Supply Air Temperature near the air handler (in a straight duct run if possible).
• Calculate the Temperature Rise = Supply Air Temperature - Return Air Temperature
  • Normal Heat Pump Temperature Rise = 15 - 20 deg.
    • High Temperature Rise = Low Airflow → Step 6. Check Indoor Air Flow

6. Check Indoor Airflow

• Remove Air Filter and Check for a Dirty Indoor Coil
  • If Indoor Coil is OK ⇒ Re-Check Temperature Rise with the filter removed.
    • No Change = Restricted Ductwork or Low Blower Speed → Step 7. Check Duct Static Pressure
    • Temperature Rise Becomes Normal = Clogged Air Filter → Replace Filter & Re-check Pressures

7. Check Duct Static Pressure

• Check the return static pressure (between the air handler and filter if possible).
• Check the supply static pressure.
  • High Static = Above 0.5" w.c.
    • High Return Static + Low Supply Static = Restricted Return Ductwork
    • Low Return Static + High Supply Static = Restricted Supply Ductwork
  • Static Pressure Normal ⇒ Increase Blower Speed or Clean Blower Wheel