American Standard Air Conditioner Error Code 6

Error code 6 indicates an indoor air thermistor fault, meaning the control board is receiving an abnormal signal from the temperature sensor located inside the indoor unit. The sensor is responsible for monitoring return air temperature to regulate system operation. The unit may shut down or restrict operation until the fault is resolved. A technician should test the thermistor resistance and inspect the wiring harness to identify the cause.

The unit should not be forced to run while error code 6 is active. Without a functioning indoor air thermistor, the control board cannot accurately regulate temperature or compressor cycling, which can lead to improper operation or potential damage to system components. It is best to leave the unit off until the fault is diagnosed and repaired.

A power reset may temporarily clear error code 6, but if the underlying fault with the thermistor or its wiring is still present, the code will return once the unit attempts normal operation. Resetting without fixing the root cause is not a solution and can mask the problem. The thermistor and wiring should be properly inspected and tested to achieve a lasting repair.

A knowledgeable DIYer can check for a loose or disconnected thermistor connector at the control board, which sometimes resolves the fault without any parts. However, testing thermistor resistance requires a multimeter and some familiarity with reading resistance values. Replacing the thermistor or control board involves working inside the unit and is generally better suited to a qualified technician.

If only the thermistor needs replacement, repair costs are typically low, often in the range of $75 to $200 including parts and labor, since the sensor itself is an inexpensive component. If the control board is the root cause, repair costs rise significantly, generally falling between $250 and $600 or more depending on the model and labor rates in your area. A diagnostic visit alone may cost $75 to $150.