Radiator fan plus AC?????

I have a 98 cavalier. I replaced my thermostat and the belt thinking that was why it was overheating badly. Only to find out that the radiator fan ONLY comes on "IF" the AC is on. Turn AC off and the fan shuts off.
Anyone have any clues on this one?? This is a new fault for me.
Dan

The radiator fan only comes on when the engine is -really- hot. Mine kicks on at about 225F. I'm not sure what to do though. Might be a relay.

if fan does'nt come on at all w/ac off sounds like engine temp sensor.located on/around thermostat housing

additional info:
When engine is completely cold like sitting over night. if you start engine and tunr on AC the radiator fan comes on. So no matter what the engine temp is, if AC is not on radiator fan is not on but if AC is on fan is on, regardless of temp.
So I am not sure if it is temp sensor or not???
Dan

Yeah, turning on the A/C turns the fan on, but the engine temp sensor seems about right.

This does not mean just leave your AC on all the time. Seems like the obvious but there are reasons for this. First change the sensor to be sure of the readings you are receiving. Are you overheating in that you have steam coming from under the hood gurgling sounds, coolant loss or is it that the temp gauge is reading high. Back to point, leaving the AC on at start up will send irregular voltage charge to different components of the system eventual causing a problem somewhere, a very comon spot on these cars (especealy the ohv) is the blower motor resistor, you most likly have a problem here if not all the fan speeds for the AC/heat work. This is a little off topic but I wanted to explain why.

I wasn't suggesting turning on the A/C all the tim. My radiator fan has only kicked on once with the A/C off, and that was when I was revving it place for about 5 minutes. It's never turned on while driving. I would assume in city driving it would turn on quite a bit due to the lack of air circulation that is found in country/highway driving.

most likely the coolant temp sensor IS BAD like stated in post#3

if your sensor is indeed bad you will have a check engine light on

Well i have replaced the thermostat and the coolant temp sensor. Fan still comes on if AC is turned on. even after being parked all night long. I am out of clues now. not sure what the real issue is. Yes the car was getting VERY hot nearly to the end of the white part of the gauge.
So folks, what next step??
Dan

Well i have replaced the thermostat and the coolant temp sensor. Fan still comes on if AC is turned on. even after being parked all night long. I am out of clues now. not sure what the real issue is. Yes the car was getting VERY hot nearly to the end of the white part of the gauge.
So folks, what next step??
Dan

The fans are supposed to kick on when the AC is on.....That is the way it is designed to work... it is not a problem... If the sensor was bad it could read hot at the gauge even if it is running at normal temp. The cooling system is pretty straight forward, is there any squeaking from the water pump?

yes, when your a/c is on your fan WILL be on, that is because your a/c condenser is right next to the radiator, for your a/c to make cold air it needs air blowing through that condenser. that part is working correctly!

did you bleed your system when you changed the thermostat?? that is MANDATORY!

also, just cuz a thermostat is new doesnt mean its good, ive heard of people going through 3-4 thermostats before finding a good one.

so, did you bleed your system?

Yes I did bleed the coolant system. Tomorrow will be the test drive to work and back and I will not use the AC system just to see if the temp gauge stays in the NORMAL or middle heat range. I did not know that the fan came on if you turned on the AC system. That was news to me! THANK YOU very much. I thought I was loosing my mind with that.
Now, the fan used to run a few seconds on its own with the key off after a long drive. This I took to be normal operation. At this point I just want it to run at normal or middle of the temp gauge without having the AC on to turn the fan on.
Wish me luck tomorrow.
Dan
Also, THANK YOU all very much for your great advice!!!!!

Well, the radiator fan wont turn on unless the engine temp is in excess of 220F, A/C excluded. I can only imagine these temps in city driving.

Well I made it to work just fine, in fact it ran a lot cooler than it used to untill i was almost at work. plus it was a cool morning. but the temp gauge never went past half way, which is where it used to go to and stay for all my driving. now we shall see how the drive home goes.
Dan

Sounds like you may have it licked, let us know.

Yeah, about halfway is your car's "happy" temperature.