York Heat Pump: Yorkguard IV & Yorkguard V
Re: Flashing Code 4 / Compressor Won't Run
Code 4 = Low Compressor Discharge Temperature
- Code 4 is sometimes listed as "Compressor Not Operating", as this is one of the more likely causes. (see Possible Causes below)
The Yorkguard IV & V have the same functionality for a Code 4:
- If, after energizing the compressor contactor for 1 hour, the Yorkguard module senses a compressor discharge temperature lower than 90 deg. the unit will enter a Code 4 lockout which disables compressor operation.
||Burnt Compressor Terminals
||Excess Refrigerant (no expansion valve)
||Bad Discharge Sensor
||Extreme Low Outdoor Temperature
1. Check Outdoor Unit
- Make sure the thermostat is set correctly and calling for heat or cool.
- Remove the access panel of the outdoor unit.
- Compressor & Outdoor Fan Operating → Step 5. Check Pressures & Temperatures
- Compressor Not Operating ⇒ Check for 230V inlet power on the compressor contactor.
- No Power → Step 2. Check Compressor/Capacitor
- Power Present ⇒ Check Diagnostic Light on Board
- Diagnostic Present ⇒ Reset the control by momentarily removing "R" and "Y" from the board. Short the Test pins if necessary to speed-up the ASCD timer.
2. Check Compressor/Capacitor
- Pull the service disconnect switch.
- Check for Short
- Check for resistance between each leaving leg of the compressor contactor & ground.
- Any Resistance = Electrical Short ⇒ Remove the wires at the compressor terminals and check the compressor seperately.
- No Resistance/Short ⇒ Check the Compressor Windings
- Check Compressor Windings
- Remove all three compressor leads from the contactor & capacitor.
- Check resistance between each lead (C & S), (C & R), (S & R).
- Resistance Between All → Step 3. Check Breaker
- No Resistance Between (C & S) and (C & R) = Over-Heated Compressor, Burnt Compressor Terminal or Bad Compressor → Check Compressor Temperature & Terminals.
- Any Other Missing Resistance = Burnt Compressor Terminal or Bad Compressor ⇒ Check Compressor Terminals.
- Check Starting Amps
- With winding resistance correct, restart the unit while monitoring compressor amperage.
- Compressor Pulls High Amperage + Does Not Start ⇒ Remove power by pulling disconnect and check capacitor.
- Capacitor OK ⇒ Add a Hard-Start Capacitor
- Still Won't Start = Bad Compressor
3. Check Breaker
- Check the unit breaker at the breaker panel and reset if necessary.
- Re-insert the service disconnect plug to restore power to the outdoor unit.
- Re-check for 230V on the contactor inlet.
4. Check Contactor
- Check the condition of the compressor contactor.
- Contactor Pulled-In + No Compressor Operation ⇒ Check for 230V across the leaving legs of the compressor contactor.
- Inlet Power + Outlet Power + No Compressor Operation = Over-Heated Compressor or Burnt Compressor Terminals ⇒ Check compressor temperature & terminals.
- Inlet Power + No (or low) Outlet Power = Bad Contactor
- Contactor Not Pulled-In ⇒ Check for 24VAC across the contactor coil.
- 24VAC Present + Not Pulled-In = Bad Contactor
- No 24VAC Present ⇒ Re-check thermostat & diagnostics.
5. Check Pressures & Temperatures
- Turn off power to the outdoor unit by pulling the service disconnect or turning off the breaker.
- Hook-up refrigerant gauges to the pressure ports on the unit.
- Blue --> "True Suction" Low Pressure
- Red --> High Pressure (either refrigerant line)
- Re-apply power to the outdoor unit.
- Start the compressor with a call for heating from the thermostat.
- Observe refrigerant pressures as the system operates.
- Allow the system to operate for at least 5 - 10 minutes.
- Normal R-22 Pressures = 25 to 65 psig Suction, 150 to 270 psig Head.
- Normal R410A Pressures = 85 to 130 psig Suction, 200 to 400 psig Head.
- Hook an insulated thermistor to the discharge line and check temperature.
- Normal discharge temperature = 130 to 160 deg.
6. Check Discharge Sensor
- Pull the service disconnect switch.
- Remove the discharge sensor wires from the board.
- Set the mulit-meter for 200K Ohms.
- Check the resistance across the sensor (see York Sensor Resistance Chart).
- Compare the sensed temperature to the actual compressor discharge temperature.