Haha, don't worry about it. Running the heater isn't going to help cool your car off much, the reason you don't want to run the A/C when it's hot and your'e just sitting is because when you turn on the A/C the motor has to work harder to drive the A/C compressor, so it gets it hot faster. If you're moving it's one thing because you can get a good amount of cool air through the radiator, but if you're just sitting you can't cool the motor off. I don't personally think that running the heater is going to draw enough heat off the motor in any way to make a difference, plus, you don't want to bake yourself in your car!

 

wait so why is it when im driving my dads 94 3.4L and it starts getting hot and i turn on the A/C the temperature drops a ton?

 

He said thermostat not gauge.

 

The heater works as an auxiliary radiator, ittakes the heat out of the engine and dumps it into the passenger compartment. So if the engine starts to overheat, turn off the AC, turn the heater to max, and open the windows.