Car goes to Hot when idle

When sitting at a red light or drive thru, my car goes to "H". I have to accelerate the gas pedal (in PARK) to make it go back down. I put a new compressor in less than two years ago and I have replaced the freon. I know for a fact that the freon is leaking, but I don't know what is causing the other. Apparently the mechanic does not either.

so your temperature gauge on your dash goes to "H". You do know that that is irrelevant when it comes to your freon; your R134a cooling system is independent of your vehicles cooling system. The only thing that "freon" does is cool the cabin of the vehicle.

If the temperature gauge on your dash goes to "H" you have a problem in your vehicles Engine Coolant system. Namely, your antifreeze, radiator hoses, heater core, water pump, radiator fan, and radiator. It is difficult to say what could be your problem though, usually the first thing you are going to want to do is flush your cooling system. This should clean it out well enough you can get some loose deposits out and that may clear up your problem. Also, if your radiator fan, radiator fan relay, or coolant temperature switch isn't operating correctly, your radiator fan won't kick on, and it won't draw air across the radiator to cool the antifreeze. And you definitely need air to come across the radiator, and it will not if you aren't moving and your fan isn't working for some reason. That would explain why your car only overheats at a stand still, and doesn't when you are moving. If your water pump doesn't work right, or is close to seizing then it isn't going to keep your coolant moving, well enough though it isn't very likely that this is your problem because usually it just seizes and your car will overheat no matter what.

I'd start with the coolant flush if you haven't recently then move down the list as i have mentioned things. If you go to do this yourself, many things can be found in the stickied posts at the top including a service manual for the 3g Eclipses, Also take note that if you do this yourself you will not be able to return any purchased electrical parts to your local autoparts store. Specifically the radiator fan, and relay are yours indefinitly once they are installed and in some circumstances when you walk out of the store. Also note that if you purchase an item at an autoparts store and install it, you will not be able to return it because it did not fix the problem, i'm not saying you will, but too many people think that a parts store is a friend that has parts you borrow to fix problems. This is not the case. Parts people can become your worst enemy if you piss them off as well, and you need them, so don't upset them.

All of this sounds very logical after being explained. I would like to emphasize that I was told that the freon did not have anything to do with the gauge going to H. I did not express that clearly I guess. I have a freon leak, too. Thank you very much!

I would say replace your thermostat...that may be one reason your temp gauge keeps going up. And what Elchico said...

thank you. I wondered about that too.

damn, that is what i forgot. thermostat! score, thanks for the addition.

oh, and i speak from personal experience, if you have a freon leak, do not use the stop leak stuff at autoparts stores, it works TOO well, and it seized my comperessor, a much more expensive fix than the small leak i had tried to fix.

ALSO: if you replace your thermostat, pay the extra money and have an original Mitsubishi one put in there, you do not want an aftermarket thermostat.

The fix is most likely even more simple than that.
Check your coolant level. Not whats in the overflow, but when the car is cool pop the cap off the radiator. If you don't see fluid add some until its full. Then top off your overflow bottle.

If this is the problem then I recommend you find another mechanic because the one your going to is either setting up to rip you off, or he's a complete idiot. If your lucky this is whats wrong.
It's recommended that you change your coolant every year. And your coolant level DOES go down over the course of that year. I'd check it every time you change your oil.