York Air Conditioner: CMB

Re: Compressor Not Running

The contactor is pulled-in but the compressor is not operating.

• No Compressor Amperage
• Equal Suction & Discharge Pressure

CHECKOUT:

1. Check 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.
• Re-apply power to the unit by re-inserting the service disconnect plug.
• Check for 230VAC power entering the contactor.
  • Power Present --> Step 3. Check Capacitor

2. Check Compressor for Short

• Remove potential power from the unit by pulling the service disconnect.
• Check for a "Short-to-Ground" on the inlet power.
  • At the contactor, check for resistance between both inlet power legs and ground.
    • Any resistance = Electrical Short
      • Remove inlet power from the contactor and re-check the inlet wiring and contactor separately.
• Check for a "Short-to-Ground" on the outlet power.
  • At the contactor, check for resistance between both outlet power legs and ground.
    • Any Resistance = Shorted Component
      • Remove the compressor wiring (all 3 legs) and check resistance between each compressor terminal & ground.
        • Any Resistance = Shorted Compressor Windings
• If no electrical short is identified, check the breaker at the breaker box and reset if necessary.

3. Check Capacitor

• Remove power to the unit by pulling the service disconnect.
• Remove the wires attached to "C" and "HERM".
• Confirm MFD reading with capacitor rating.
  • Less than 80% of rating = Bad Capacitor
• SWITCH METER LEADS BACK TO COM AND V BEFORE PROCEEDING!

4. Check Compressor Windings / Overload

• Remove power from the unit by pulling the service disconnect.
• Remove the compressor "Common" wire, either at the contactor or at the compressor.
• Check resistance of the compressor windings from "Common" to "Start" and "Common" to "Run".
  • Resistance Between Each Winding = Compressor Ready to Start --> Step 5. Check Compressor / Contactor
  • No Resistance on Either Winding = Burnt Compressor Terminal, Open Compressor Windings or Internal Overload Open
    • Check the compressor temperature
      • Cool Compressor + No Resistance = Open Windings or Burnt Compressor Terminal
      • Hot Compressor + No Resistance = Internal Overload Open
        • It may be necessary to cool the compressor with water until the overload resets.

5. Check Compressor / Contactor

• Check to see if the contactor is physically pulled-in.
  • Not Pulled-In --> Check for 24VAC across the contactor coil.
    • Power but Not Pulled-In = Bad Contactor
    • No Power = Thermostat not Calling or Safety Tripped
• Re-apply line voltage power by re-inserting the disconnect plug.
  • Compressor Hums but Doesn't Start = Locked-Up Compressor
    • Add a "Hard-Start" and Re-Try
  • Compressor Doesn't Run or Attempt to Start:
    • Re-check for 230VAC inlet power at the contactor.
    • Check for 230VAC outlet power at the contactor.
      • Contactor Pulled-in but No Power = Bad Contactor