Over heating but AC wont turn off?

Asked by Jun 06, 2015 at 06:00 PM about the 2005 Pontiac Grand Prix GTP

Question type: Maintenance & Repair

I have a 2005 Grand Prix GTP. I went to pick up my son from daycare the other day
and heard what sounded like my tire losing air at a rapid pace. I went around the front
of the car and noticed I could hear it better standing at the front of the hood. I waited a
minute and opened the hood to see coolant dripping down from the hood up near the
reservoir. I didn't drive the car again until today when I was going to pick my son up
from his dads house HOPING it couldn't over heat and I could just let it sit after that
until I can get it fixed. But as I was driving the temp gauge was continuing to rise so I
attempted to crank my heat full blast. instead of heat though all that came out was
freezing cold air. I had the temp up at 90 on my thermostat on the dash. The car
started to over heat and my display told me it was going to turn off the ac to help. So
the ac turned off and my car stopped making it's way into the red zone and started
cooling down pretty fast.
Have any idea what could cause this?

2 Answers

71,585

Sounds like you're very low on coolant due to a leak. You were right by turning on the heat but you got cold air due to the low coolant. Your automatic climate control runs the air conditioning system full time to dehumidify the air in the passenger's compartment even when heat is selected. This helps prevent window fogging on cool damp days. Because the a/c system puts an added heat load on the cooling system the computer will shut it down if the engine starts to overheat. Refill the cooling system and check for leaks. I suspect a hose or possibly the water pump has sprung a leak. HTH. -Jim

4,385

There are a couple of small plastic elbows that take coolant to the heater core. They all fail eventually and you loose all your coolant. That is most likely the problem. The parts are about $5. Shop/do-it- yourselfer time is about 2 hours and of course you'll need new coolant. In the mean time don't run it for more than a few minutes at a time or you'll overheat the engine and wreck something.

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