Overheat protection (Outdoor pipe thermistor)

What does Ud mean?

This fault triggers if the outdoor pipe thermistor (TH1) detects 70°C (158°F) or more during compressor operation. It indicates excessive heat within the outdoor unit, likely due to restricted airflow, a malfunctioning outdoor fan, or a faulty thermistor. Persistent overheating can lead to compressor failure and significant reduction in cooling efficiency.

• Blocked outdoor condenser coils with dirt, dust, or debris, restricting heat rejection and causing high refrigerant temperature.
• Malfunctioning outdoor fan motor or fan blade obstruction, leading to insufficient airflow across the condenser.
• Overcharge of refrigerant causing elevated system pressures and higher condensing temperatures.
• Faulty outdoor pipe thermistor (TH1) providing an inaccurate high-temperature reading to the controller.
• Ambient temperature exceeding system design limits, overwhelming the heat rejection capacity.

Click steps to track your progress.

1. 1

   Power off and thoroughly clean the outdoor condenser coils using a fin comb and appropriate coil cleaner.

2. 2

   Verify the outdoor fan motor is operating at its commanded speed (e.g., using a tachometer) and the fan blades are free of obstruction.

3. 3

   Measure the resistance of the outdoor pipe thermistor (TH1) at ambient temperature and compare it to the sensor's resistance-temperature chart.

4. 4

   Verify the refrigerant charge using a manifold gauge set, ensuring subcooling is within manufacturer specifications (e.g., 5-10°C).

5. 5

   Check for proper airflow across the condenser by measuring air velocity at the fan discharge (e.g., using an anemometer).