Code 53-41 OST Open - Suction Thermistor is open, heating mode locked out.

What does 53-41 mean?

The outdoor suction thermistor (OST) is detected as 'open' (resistance above 465kohm). This sensor is crucial for controlling the outdoor EXV in heat pump systems, so heating mode will be locked out. Cooling operation may still be permitted, but a malfunction will display on the wall control, often showing '47'.

• Break in the suction thermistor wiring.
• Break 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 above 465kohm, inspect the thermistor wiring and its connector for any breaks or loose connections.

3. 3

   If no breaks 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.