Code 53-42 OST Shorted - Suction Thermistor is shorted, heating mode locked out.

What does 53-42 mean?

The outdoor suction thermistor (OST) is detected as 'shorted' (resistance below 1kohm). Similar to an 'OST Open' fault, heating mode operation in HP systems will be locked out. Cooling operation may still be allowed, but the wall control will display a malfunction, often showing '47'.

• Short circuit in the suction thermistor wiring (e.g., bare wire).
• Short circuit at the thermistor connector.
• Faulty suction thermistor sensor.
• Faulty PCM if thermistor resistance measures within range.

Click steps to track your progress.

1. 1

   Measure the resistance value of the suction thermistor at the PCM connector.

2. 2

   If the measured value is below 1kohm, inspect the thermistor wiring and its connector for any bare wires or short circuits.

3. 3

   If no bare wires or shorts are visually observed, replace the suction thermistor sensor.

4. 4

   If the measured resistance is within the allowable range, the PCM (Processor Control Module) may be faulty and require replacement by a qualified technician.