Tonight my heater stopped working and it feels like the AC is on. The heat stopped coming out of the floor vents then cold air started coming out of the dash vents. I shut the car off and started it up again and it acted like it does in the summer with AC kicking on I popped the hood and sure enough the compressor was running.

Any ideas?

 

I would try putting the unit into manual mode to see if you can override the computer. But, it may be that your computer module has fried itself and is now acting up.

Out of curiosity, 2 things I would look at. First, if you have the automatic temperature control (which it sounds like you do), did the temperature by some magical reason get dialed all the way down. That could cause what you are seeing. Secondly, try pulling the fuse for the temp control unit to force it to clear what it currently is set up like. From there, you can re-install the fuse and the unit will start all over again. That might be all that it takes to get it functioning again.

 

Bailey, it is possible that there is an open in your interior temp sensor or there is an issue with the temp control unit. Let me look at the diagrams and see what we are talking about here.

Please let me know if you have the automatic temp control or if you have the manual temp control setup. This may affect what is possibly wrong.

 

Bailey, short of having a problem with the climate control module, about the only thing that would cause what you are seeing is a failed interior temp sensor. It is located behind the dash, to the right of the steering wheel. If the temperature element opens up, this would make the computer think that the temperature inside the car is very high, which would then kick in the A/C and cause it to blow out cold air.

You can prove this being the case by simply taking the car out of "auto" and then dialing the temp up to force the heat on. If you can get heat that way, pretty much points to the temp sensor. If you still can not get heat, then I would be looking at the climate control module.

 

Check your coolant Level. If it is low, the heater won't blow warm air. My 02 has a slow coolant leak and I know when its getting low because my heater will start blowing cold air. Once I top it off, good ol' heat again.

 

I disconnected the battery overnight and topped off the coolant, it was not real low half way between the Max and Min level, and the heat came back.

 

Glad to hear it. Always good when it is an easy fix.