Q: My car is moving the Ac get cold if I stop the signal or park the Ac get hot

asked by on August 23, 2016

My car is moving the Ac get cold if I stop the signal or park the Ac get hot
My car has an automatic transmission.

This is a classic symptom is very common. Most likely the cooling fan for the condenser is not turning on allowing the high side of the A/C system to get to hot. This reduces the cooling capacity of your system. The cause can be the fan motor, a cycling switch, or a temperature switch depending on the design of the system in your car.

After looking at the wiring diagram of your Kia Optima, it appears the fan is turned on and off by the PCM (Powertrain Control Module). The PCM receives a signal from a pressure transducer. The transducer lets the PCM know how hot the condenser is and determines when the fan should be turned on. Between the PCM and the fan motor is a relay. Relays are excellent points to diagnose a system such as this.

From the relay you can supply power to the fan motor with a jumper wire and see if it turns on. If it does, you know it is either the relay, the PCM (not common), and the pressure transducer. You can run the car until the A/C system output begins to increase in temperature, then use a test light to see if the PCM is commanding the relay on. If it is, you need a relay. If not, you should begin by replacing the transducer. They are a common failure item, PCM’s rarely fail and are very expensive.

If you need some help with this, feel free to contact a certified technician, like one from YourMechanic. They’ll be able to diagnose the issue with your A/C and help you fix it accordingly.

Good luck!

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