Pontiac Repair: 2001 Montana a/c, intake manifold gasket, coolant temp

Question
I recently had the a/c condenser replaced on my 2001 Montana.  The R134a level is right at spec.  When the car is at idle it blows nice cold air.  When going down the road it blows warm air.  also if the a/c is off the engine starts to overheat.  When the a/c is turned back on the temp gauge comes back down to normal.

Answer
Hi David:

This has the reverse of what I would think would happen. I would look at the coolant level first and foremost if it's low on antifreeze it will over heat. possible a lower intake manifold gasket. If it's low on coolant it can trick the coolant temp sensor which in turn controls the coolant fan(S) for the radiator. when you tune the a/c on the coolant fan will turn on when the a/c pressures are high enough with the fan on it cools the negine down enough. That I think is what is going on here. good luck :)

Oh P.S. check the coolnt level when the engine is cold so you don't burn your self!