When I drive with the a/c on, it blows cold. When I let it idle, the air gets warm, I can tell the a/c is cycling on and off, and the car gets hot. Also, even at around the 240 mark, the fan never kicked on. Then when I turned the car off, I heard the coolant res. boiling. However, when I'm driving down the road, everything works fine. The only thing I could think was that, because the fan doesn't turn on, the engine gets hot, because the engine gets hot it cycles the a/c which makes the air hot. Is this completely out to lunch? Anyone have any ideas on how to fix this?

Well I have a theory and it is just a theory. First of all check you fluid level. They boil over more when they are low. Do you have the dual fan set up or single? The reason your air is getting warmer is because you are low on freon. That makes the compressor kick on and off. When it kicks off, you get warm air. I think that has nothing to do with the fan not kicking on except one of your fans is triggered when you turn on your air (if its fully charged) because it works off of pressure in the a/c system.. The other one comes on at around 240 I believe. So it sounds to me like your fan or fans are not working because neither come on. If its the single fan set up, it should still come on when the temp gets to 240. I would test the fan(s) to see if they work. If not then there are several threads on here that tell you what to check. I hear relays are often the culprit. Again this is a theory and someone else please verify my information who knows more about this.

Third Gen Primary and Secondary Engine Fans

dave8412 Jun 16 2006 - 9:49am Q: When do the primary and secondary fans kick in?
A: According to the 1990 service manual, the primary fan is controlled by the ECM and will come on when the coolant temperature reaches 190 degrees F. The secondary fan has its own temperature sensor in the bottom of the engine block (passenger side) and will turn on when both of these conditions exist:
The coolant temperature is greater than 222 degrees F
When the A/C control head pressure is greater than 1600kPa and the vehicle speed is less than 40 mph.
The Auxiliary Coolant Fan is controlled by the A/C Pressure switch and the auxiliary coolant fan switch. It is not controlled by the ECM. It should have black and black/pink wires going to it, and the coolant fan will have black and black/red wires going to it.Found this in the FAQ section.

You didn’t say if you have one or two fans.

However a fan needs to come on IMMEDIATELY, regardless of the pressure whenever you use AC or defrost.

For further diagnosis state whether you have one or two fans.

There's just one fan on the back of the radiator. It's a 91 5.0TBI

I didnt know that. I have the single fan set up and it does not come on when I turn on the ac. It only comes on when the temp goes up to like 240. Sorry to hi jack but...Any suggestions?

the fan provides air flow to the a/c condenser at idle. with out it the head pressure will climb out of control thus you get hot air! the compressor cycling does not cause the hot air the lack of air flow to the condensor does. fix the fan/s and you should be good.

Well that makes sense. My theory was wrong then. My ac doesnt work so I just figured thats why my fan didnt kick on when I turn on the ac.