Heat Pumps: Heating
Re: Blows Cold Air / Runs Continuous / Outdoor Unit Not Running
When the customers reports that their heat pump runs continuous and blows cold air, this is generally caused by an inoperative compressor.
► As long as the auxiliary heaters are working, the temperature in the space will still be at or near the heating setpoint.
| Possible Causes (From Most to Least Likely): |
Qty |
| Bad Capacitor |
1 |
| No Power to O/D Unit |
|
| Bad Compressor |
|
| Refrigerant Charge |
|
| Defrost Problem |
|
| Ductwork Problem |
|
CHECKOUT
1. Check Outdoor Unit
2. Check Power
- Disconnect power to O/D unit by pulling disconnect or turning off breaker.
- Open the electrical compartment cover.
- Inspect for burnt wiring or burnt contactor contacts.
- Re-apply power to the unit.
- Check for 200 - 240VAC power on the contactor inlet.
- No Power = Tripped Breaker or Bad Wiring
- Check for 24VAC between "R" and "C" on the defrost control board.
- No Power = Blown Low Voltage Fuse or Bad Transformer
- Set the Thermostat to call for heat.
- Check for 24VAC between "Y" and "C" on the defrost control board.
3. Check Compressor Operation
- Check Compressor Amperage to ensure that the compressor is operating.
- Compressor Does Not Try to Start = Safety Lockout or Bad Contactor
- Check for 24VAC between the Yellow wire on the Y terminal and "C" on the defrost board.
- Check for 24VAC between both sides of the contactor coil.
- Power at the defrost board but not the contactor = Open Hi or Lo Pressure Switch
- Power on both but contactor not pulled in = Bad Contactor
- Compressor Hums but Doesn't Run = Bad Capacitor, Locked-up Compressor, or Burnt Compressor Wiring
4. Check Refrigerant Pressures
- Hook-up refrigerant gauges to the pressure ports on the unit.
- Blue --> "True Suction" Low Pressure
- Red --> High Pressure (liquid line)
- Monitor pressures as the system operates.
| Normal Pressure Range |
| Refrigerant |
0-30 Deg O/D |
30-50 Deg O/D |
| R-22 |
- 20-40 Suction
- 150-225 Discharge
|
- 40-75 Suction
- 170-260 Discharge
|
| R410A |
- 75-100 Suction
- 250-320 Discharge
|
- 100-150 Suction
- 250-375 Discharge
|
- Low Pressure Issues
- Low Suction + Low Discharge + Metering Device Frosting = Low Refrigerant Charge
- Try adding refrigerant through the Low Pressure gauge.
- Suction and Discharge Pressures should gradually increase as refrigerant is added.
- High Pressure Issues
- Place an insulated temperature probe on the liquid line.
- 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 = Refrigerant Overcharge or No Indoor Blower
- 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 Expansion Valve
- Sub-Cooling < 2 deg. + High Discharge = Low Indoor Heat Transfer --> Step 6. Check Air Temperature Rise
5. Check Compressor Discharge Temperature
- Use a multi-meter to check the temperature of the compressor discharge line.
- Normal Temperature = 120 - 150 deg.
- Low Discharge Temp = Inefficient Operation
6. Check Air Temperature Rise
- With the auxiliary heaters disconnected (remove "W1" and "W2" form the air handler terminal block):
- Check the Return Air Temperature near the unit or in the filter compartment.
- Check the Supply Air Temperature.
- Normal Temperature Rise = 15-20 deg.
- Abnormally Low Return Air Temperature --> Check Return Ductwork for Cold Air Infiltration
- Low Temperature Rise = Inefficient Operation
- High Temperature Rise = Low Airflow
- RE-HOOK "W1" AND "W2" WIRES ON THE AIR HANDLER!
