On a related topic (not wanting to steal this thread) I have a 1999 Galant that was overheating and before that happened the AC was blowing hot when just a few days earlier it worked fine. Does that mean anything in either case?

 

I had replaced the radiator, temp sensor, water pump and thermostat. This didn't solve the problem.

I noticed the AC was getting hot when idling. I checked the condenser core in front of the radiator with a infrared gun and noticed it was getting really hot even though the electric fan was running. I also noticed the fan clutch felt weak. So I replaced the fan clutch and it helped some but didn't fix it.

Since the compressor was making a racket and was invariably ready to fail, I replaced it, the drier and the evap valve. Sucked and pumped the system and voila the gauge started working correctly.

Hard to know the exact problem but it seemed that somehow the heat from the core and Ac system was bleeding into the cooling system at idle or when the car had been stopped and was started again after it had been running. The gauge always worked correctly in the mornings after sitting all night.

All the other mechanics I have discussed this with have never encountered this or have never looked at the a/c when the car was overheating. One mechanic thought that maybe the electronics were somehow coupling the a/c signal into the temp electronics when the a/c was bad. Others were skeptical that this was the problem.

All I can say is that it fixed my problem.

 

UPDATE!!!! I took it into the shop, they tested waterpump, checked head gasket, fans, radiator flow, thermostat, and everything was working properly. At full pegged it was at 206 which was normal. The gauge was wrong, giving me false temps.

 

So, it wasn't your a/c?