Yorkguard - Flashing Code 4

Article ID: 128
Last updated: 6 Feb, 2023

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.

Qty Possible Causes:
1 Tripped Breaker
1 Bad Capacitor
2 Bad Compressor
Bad Contactor
Burnt Compressor Terminals
Excess Refrigerant (no expansion valve)
Bad Discharge Sensor
Extreme Low Outdoor Temperature


1. Check Outdoor Unit

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.

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Article ID: 128
Last updated: 6 Feb, 2023
Revision: 24
Access: Public
Views: 641
Comments: 0
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