Denso Air Conditioner Error Code RT

The RT error code indicates a room thermistor defect, specifically a short circuit or open circuit detected on the room thermistor connected to connector J101 on the indoor unit's control board. The room thermistor is the sensor responsible for measuring the ambient air temperature inside the space. When the control board cannot read a valid resistance value from this sensor, it triggers the RT fault and suspends normal operation.

It is not recommended to continue operating the unit while the RT fault is active. Without a functioning room thermistor, the control system cannot accurately regulate temperature, which can lead to improper compressor cycling or the unit running outside of safe operating parameters. The system may shut down automatically as a protective measure, and the underlying fault should be addressed before resuming normal use.

A power reset may temporarily clear the RT error code from the display, but if the underlying fault with the room thermistor or its wiring at J101 has not been corrected, the error will return once the unit attempts to read the sensor again. A reset is only a useful step if it follows a physical repair, such as reseating the connector or replacing a confirmed faulty thermistor.

The first step is something most homeowners can attempt: disconnect the room thermistor connector at J101, inspect it for damage or corrosion, and reconnect it firmly. If that does not clear the error, testing the thermistor with a multimeter and replacing it if it reads open or shorted is a straightforward repair, though it does require basic electrical comfort and access to the indoor unit's control board. If the control board itself is at fault, professional service is recommended.

If only the room thermistor needs replacement, parts typically cost in the range of $15 to $60 depending on the specific model, with professional labor adding $75 to $200 depending on your location and the technician's rates. If the control board's thermistor input circuit has failed, a full board replacement can range from $150 to $400 or more for parts alone. Reseating a loose connector costs nothing if you do it yourself.