Hot and cold running Town Car

Q: I have a 1994 Lincoln Town Car and have experienced a problem with the air-conditioner system. It works fine, then all of a sudden, instead of cool air, it feels like a blast furnace. It will run this way for a bit and then return to cool air. Pretty soon the blast furnace returns until I stop the car — which is soon, because it gets pretty hot.

The Ford dealer couldn't find anything wrong with it.

A: Your Lincoln is equipped with EATC, or electronic automatic temperature control. When auto mode is selected, EATC chooses the appropriate A/C compressor status, ventilation door position, level of temperature blending and fan speed to achieve the selected temperature.

The EATC system monitors ambient and in-car temperature, as well as sun-load, and tries to close the gap between actual and desired temperature as quickly as possible.

My hunch is your in-car temperature sensor circuit is occasionally falling victim to a faulty connection.

The system has diagnostic capability. Next time the system acts up, try this: Press the control panel's off and floor buttons simultaneously, then within two seconds, press the auto button. The system will enter diagnostic mode and possibly display error code 3, indicating a fault in the in-car temperature sensor circuit, or code 2, a fault in the blend door actuator circuit.

Armed with this information, a qualified technician should be able to track down the cause in short order.

E-mail Brad Bergholdt at under-the-hood@juno.com