York Heat Pump: YMA **INCOMPLETE**
Re: Outdoor Unit Starts Then Shuts Off
The contactor on the outdoor unit pulls-in and the unit starts running, but shuts off after a short runtime.
Qty |
Possible Causes: |
1 |
Bad Hi Pressure Switch |
|
Bad Low Pressure Switch |
|
Condensate Overflow Switch Open |
|
Losing Call for Y |
|
Low Voltage Short |
CHECKOUT:
1. Check Line Voltage Power
- Disconnect power to the outdoor unit by pulling the service disconnect.
- Remove the outdoor unit electrical access panel.
- Look for any signs of burnt wires or controls.
2. Check Low Voltage Power
- Check for 24VAC between Common (Black) and Y (Yellow).
- No Voltage = No Call from Thermostat, Condensate Overflow Switch Open or Bad Wiring
- Voltage Present ⇒ Continue
- Allow the unit to start.
- Immediately when the unit stops running re-check for 24VAC between Common (Black) and Y (Yellow).
- Power Stays On → Step 2. Check Pressure Switch
- Power Drops Out ⇒ Check Thermostat to see if "Wait" timer has restarted.
- Yes = Suspect Low Voltage Short
- No = Check Condensate Overflow Switch
3. Check Pressure Switch Circuit
- Check for 24Vac from Common (Black) to each Pressure Switch terminal on the defrost board.
4. Check Pressure Switches
- There are two pressure switches wired in series to the Defrost Board:
- High Pressure Switch = Yellow/Red Wires
- Low Pressure Switch = Gray/Pink Wires
- Find and cut the factory wire nut which connects the (Yellow/Red) High Pressure Switch to the (Gray/Pink) Low Pressure Switch.
- Check continuity across both pressure switches.
- High Pressure Switch Open = Bad High Pressure Switch
- Low Pressure Switch Open ⇒ Check Refrigerant Pressure
- Sufficient Pressure = Bad Low Pressure Switch
- Low or No Pressure = Loss of Charge
5. Check Defrost Pin Selection
- If the defrost board has recently been changed, make sure that the defrost pin is in a numbered position.
- A replacement defrost board will not energize the compressor contactor in the default "P" position.
- See Replacement Defrost Board article for details.