Heat Controller Air Conditioner Error Code 45

Error code 45 indicates an open or short circuit fault in the condenser pipe thermistor sensor. This sensor monitors refrigerant temperature at the condenser coil and reports back to the control board. When the signal voltage reads 0V (short) or 5V (open) instead of the normal 2.5V DC at 25 degrees Celsius, the unit logs this fault and may shut down the compressor to prevent damage.

It is not recommended to continue operating the unit with error code 45 active. The condenser pipe thermistor provides temperature data that the control board uses to protect the compressor and refrigerant circuit from high-pressure or overheating conditions. Without a functioning sensor, the system cannot respond appropriately to abnormal operating temperatures, which could lead to compressor damage over time.

A power reset may temporarily clear the error code display, but the fault will return as soon as the control board re-reads the sensor signal and detects the out-of-range voltage. Because the underlying cause is a hardware fault in the sensor circuit, the code will not clear permanently until the defective thermistor, wiring, or connector is repaired or replaced. Repeated resets without addressing the root cause do not resolve the issue.

Some causes of error code 45 are DIY-accessible. You can inspect the sensor connector for corrosion and check the wiring harness for visible damage without special tools. Testing the thermistor requires a multimeter: unplug the sensor and measure resistance across the leads, which should read approximately 5 kilohms at 25 degrees Celsius. If the sensor has failed or wiring is damaged, replacing the thermistor is a straightforward repair, though working inside the outdoor unit should be done with the power fully disconnected.

If only the thermistor sensor needs replacement, parts and labor costs are generally modest, typically in the range of $75 to $200 depending on the service provider and part availability. If the control board is responsible for the fault, repair costs are higher, often ranging from $200 to $500 or more. Getting a diagnostic service call first is the best way to confirm which component has failed before committing to parts costs.