Trane Heat Pump

Re: Compressor Won't Run / Compressor Can't Start

With a heat pump system, as long as the auxiliary heaters are working, the conditioned space should stay at or near the thermostat heating setpoint, but if the heat pump itself is not working the customer may report one or both of the following:

• The unit runs continuous.
• Sometimes the unit blows warm air but goes back to blowing cold air.

Checking the outdoor unit, it is found that the outdoor fan is on but the compressor is not running.

Other Symptoms:

• Every several minutes the compressor hums but does not start.

CHECKOUT

1. Check Voltage

• Check for 200 - 240VAC on the inlet side of the compressor contactor.
  • Low Voltage --> Check Power at Disconnect & Breaker Panel
• Check for 200 - 240VAC on the leaving side of the compressor contactor.
  • Low Voltage = Bad Contactor

2. Check Capacitor

• Break power to the outdoor unit by pulling the service disconnect or turning off the breaker.
• Remove wires from "C" and "HERM" of the capacitor.
• Move Meter leads to COM and MFD.
• Set Meter to 200 MFD.
• Place one lead on capacitor "C" and the other on capacitor terminal "HERM" 
• Confirm MFD reading with capacitor rating.
  • Less than 80% of rating = Bad Capacitor
• SWITCH METER LEADS BACK TO COM AND V BEFORE PROCEEDING!

3. Check Terminals / Resistance

• WITH POWER STILL OFF remove the "BK/BL" (Common) wire from the contactor.
• Remove the "OR" (Start) wire from "HERM" of the capacitor (if not already removed). 
• Removed the "RED" (Run) wire from "C" of the capacitor (if not already removed). 
• Check resistance between "BK/BL" and "OR".
  • Should read
• Check resistance between "BK/BL" and "RED".
  • Should read
• Check resistance between "OR" and "RED"
  • Should read
    • No resistance from "BK/BL" to either "RED" or "OR" could indicate internal overload trip.
    • Check compressor temperature, allow time to cool, then re-check.

4. Add a "Hard Start"

• If the above items test OK, WITH POWER STILL OFF, install a "Hard Start" on the compressor capacitor.
  • Place one Hard start lead on "C" of the capacitor and the other on "HERM" of the capacitor.
  • Re-apply power and see if the compressor is able to start.
    • Compressor still hums but won't start = Locked-up Compressor