What IS the problem? Does the air become cold, then hot? Does the fan turn off then come back on by itself? You'll have to clarify what "seems to work and then after awhile it goes off again" means.
If you get cold air:
First check the coolant level in the radiator and the overflow reservoir. If it's low in the radiator, the coolant won't circulate properly through the heater core.
What happens to the temperature gauge when you get cold air? If the gauge drops noticeably, suspect a problem related to the thermostat. In that case, the air temperature will drop gradually over a minute or two. If the gauge goes up when you get cold air, something is impeding coolant circulation. A broken water pump impeller is common on Volkswagens, but I have never heard of that on Chrysler products. Low coolant might be the cause.
If the air temperature gets cold very quickly, suspect a problem with the heater control computer. It is a very complicated and problem-riddled computer that does what used to be done with a few levers and cables. If it is unplugged, or if the battery was disconnected, the computer will have to be reprogrammed. Until that is done, there's no telling what unusual things it will cause. The six yellow leds in the buttons should be flashing if it's out of calibration. Also, to do the calibration procedure, the air conditioning must be working properly or it will not pass the cool down test as part of the calibration procedure. The actuator calibration test should be able to be completed.
If the yellow leds aren't flashing, and the battery wasn't recently disconnected, suspect a problem with the computer itself. That's what I read about most often.
If the problem relates to a loss of air flow, (the fan stops running), try it on all speeds. If it still runs on only the highest setting, there's a problem with the computer. The speed control function that used to be done with a really simple, reliable resistor assembly is now done with sensitive switching transistors in the computer module. Also suspect the computer if the fan stops running on any speed including high. The fan motor itself will not stop on its own once it is running unless there is a corroded connection in its plug, but that would be very rare.
If the fan stops running and the radio display goes off and the power windows don't work at the same time, suspect burned contacts inside the ignition switch or overheated terminals and wires in the switch connector.
Saturday, December 12th, 2009 AT 8:48 AM