Lennox XP13 Heat Pump: Heating

Re: High Pressure Fault/Lockout

There are two different High Pressure Indications:

A High Pressure Fault occurs when the Hi Pressure Switch opens and is indicated by a Slow Flashing Green LED on the outdoor unit control board.

A High Pressure Lockout occurs after the 5th High Pressure Fault during a single compressor cycle and is indicated by a Solid On Green LED on the outdoor unit control board.

► There is a schrader valve under the high pressure switch for replacement.

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

• Make sure the blower motor has power and is operating.
  • 230V Power + No Operation = Bad Blower Motor or Bad Capacitor

3. Check Refrigerant Pressures

• If the heat pump is in lockout, reset by removing 24VAC power to the outdoor control board.
• 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 (small liquid 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 Indoor Blower → Step 6. Check Air Filter & Indoor Coil
  • 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 + High Suction Suction = Overcharged
    • Sub-Cooling > 13 deg. + High Discharge + Low Suction = Bad O/D Expansion Valve
    • Pressures & Sub-Cooling Normal → Step 5. Check Defrost

5. Check Defrost Cycle

• Force a defrost cycle by jumping the Test pins.
• Monitor the refrigerant pressures and liquid line temperature as the unit runs through a defrost cycle.
• Unit should exit defrost when the liquid line temperature is between 60 - 90 deg., Hi-side pressure should be between 300 - 400.
  • High Pressure + Low Temperature = Indoor Metering Device Issue
  • High Pressure + High Temperature = Bad Defrost Thermostat

6. Check Air Filter & Indoor Coil

• 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