Outdoor Heat Exchanger Thermistor 4 Failure (Tho-R4)

What does E37-4 mean?

The fourth outdoor heat exchanger thermistor (Tho-R4) is defective. This prevents accurate temperature measurement of a specific section of the outdoor coil, impacting system control and protection.

1. 1

   Measure the resistance of thermistor Tho-R4 at its leads — compare to a resistance-temperature chart if available.

2. 2

   Inspect the connector for Tho-R4 on the outdoor unit PCB — verify it is securely seated and free from corrosion.