4TWB3 - Outdoor Unit Not Running

Trane Heat Pump: 4TWB3

Re: Outdoor Unit Not Running

• The thermostat is calling for either HEATING or COOLING.
• The Indoor fan is operating.
• Neither the Outdoor Fan or Compressor are operating.

CHECKOUT

1. Check High Voltage

• Open the outdoor unit control cabinet.
• Check for 200 - 240VAC on the inlet side of the compressor contactor.
  • No or Low Voltage ⇒ Check Power at Disconnect & Breaker Panel
• Check to see if the compressor contactor is pulled-in.
  • Not Pulled-In → Step 3. Check Low Voltage
  • Pulled-In ⇒ Continue
• Check for 200 - 240VAC on the leaving side of the compressor contactor.
  • Contactor Pulled-In + No or Low Voltage = Bad Contactor
  • Power Present + No Operation → Step 2. Check Capacitor

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 Low Voltage

• At the outdoor unit low voltage connections, check for 24VAC between "Red" and "Blue".
  • No Power = Blown Low Voltage Fuse or No Air Handler Power
• Check for 24VAC between "Yellow" and "Blue".
  • No Power = No call from the thermostat ⇒ Recheck thermostat and look for a condensate overflow switch at the air handler.
• Check for 24VAC at the compressor contactor coil "YL/RD" and "Blue".
  • No Power at Contactor + Power on "Y" = Open Safety → Step 4. Check Safeties
  • Power at Contactor + Contactor Not Pulled-In = Bad Contactor

4. Check Safeties

• At the defrost board plug, check for inlet power between "Yellow" and "Blue".
  • No Power = No call on "Y" or Broken Wire
• At the defrost board, check for 24VAC between "YL/BK" and "Blue".
  • No Power = Anti-Short-Cycle Delay or Bad Defrost Board
  • Power Present ⇒ Continue
• At the wire-nut splice, check for 24VAC between "YL/RD ⇔ RD" and "Blue".
  • No Power = Open Low Pressure Switch
  • Power Present ⇒ Continue
• At the compressor contactor, check for 24VAC between "YL/RD" and "Blue".
  • ​​​​​​​No Power = Open Hi Pressure Switch
  • Power Present + Contactor Not Pulled-In = Bad Contactor