Air conditioner and overheating

I have a problem with my 97 Taurus wagon where the temp guage starts to climb when I turn the air conditioner on. I checked the fans and they are on when the air conditioning turns on. When I turn the a/c off, the temp
quickly drops back down to normal operating temperature, even when it is 32 degrees celcius (about 90 fahrenheit) outside.
Does the fact that the engine immediately starts getting hot when I turn on the air indicate that something is wrong with the compressor?
After I turn the air conditioning off, there is a hissing as if something is leaking from the left hand side of the engine compartment to the rear of the compressor. Is this a normal depressurization or could a leak cause the overheating problem?
Coolant level and color is good. Car can idle all day in the heat with no a/c on and temp does not get above halfway.
Any ideas?
Eric
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Eric Janzen wrote:

the a/c system..... when its running the compressor is sucking the freon out of the system and that how you get cold... when you turn it off then there is no more sucking on this freon so both the pressure and suction side equalize and the hissing is what you hear... this happens with all a/c unit... the reason why your engine heats up with the a/c unit on is that it is working much harder with the a/c on....
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Thanks. Good to know that.

This I know. I guess what I was trying to say was: If the engine stays cool without the a/c on and USED to stay cool with the a/c on, would the fact that it now does not maintain a normal temp with the a/c on mean that it is working even harder than it should? That is - the compressor is screwed up or something and is harder to turn than it should be... I don't know. I guess I will wash out the fins like another poster suggested and see if that helps.
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Wash the bugs out of the condenser and radiator fins.
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It indicates a marginal radiator. The radiator is getting plugged up - inside, outside, or both. Since the A/C condensor sits ahead of the radiator in the airstream, it heats up the air before the radiator ever gets it, and the radiator is no longer able to cool adequately.
Use a hose to clean both the compressor and the radiator. That may be enough. Look inside the radiator and see if the the water passages are getting choked off by deposits. If so, it's time for radiator service, which usually means rodding it out.
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If you've got any where near 100K miles on the car with the original radiator, it's probably getting plugged up inside from corrosion. If you've never changed the coolant, it could be significantly less miles.
Bottom line is that the radiator isn't doing the job either due to capacity (corroded fins), or some other external blockage in front of the radiator (leaves or bugs). The most likely is that the radiator has lived it's life.
Oh - just to make your day, keep in mind that your heater core is just a small radiator, sharing the same cooling system, and it will wear almost exactly as long as your radiator. If you notice that the heat isn't as good as it used to be come winter time - this is why.
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