ac compressor/overheating

[redrddvl]

i have a 94 caprice 5.7, when im driving WITH the ac on the car starts to overheat but as soon as i turn off the ac the tempature goes down.Ive changed the termastat,yes both the fans are on and radiatior has fluid in it. But my ac compressor has a leak in it could it be that when im running the ac with very little coolant or none at all could cause this problem. I need help i hear all these different things but dont know what to do. Oh i just also changed the plugs and wires

[silicon212]

Originally Posted by redrddvl

i have a 94 caprice 5.7, when im driving WITH the ac on the car starts to overheat but as soon as i turn off the ac the tempature goes down.Ive changed the termastat,yes both the fans are on and radiatior has fluid in it. But my ac compressor has a leak in it could it be that when im running the ac with very little coolant or none at all could cause this problem. I need help i hear all these different things but dont know what to do. Oh i just also changed the plugs and wires

The symptoms you lay out are consistent with an overcharged system, not an undercharged system. If it has a leak in it, there's a chance that you put too much refrigerant in it to compensate. Bleed some off and see what happens.

Another possibility is a restriction in the cooling system somewhere, or an improperly functioning water pump.

[PeteA216]

Another possibility is a restriction in the cooling system somewhere

I had the same problem with my Caprice when I swapped the engine from a 5.0 305 to a 5.7 350... I reused the radiator from the 305 and once I got the fan situated ity was fine, never exceeding 180 degrees, but as soon as I put on the A/C, which was properly charged, the engine temperature started climbing up past the 200 degree mark. Out of worry I turned off the A/C before it got too hot. There is the possibility that your radiator is clogging, and it flows just enough to keep the engine cool under normal conditions, but once the load of the compressor is added along with the heat of the condensor the radiator just may not be able to keep up. Another possibility is the lower radiator hose could be collapsing in on itself due to it's age, thus causing a coolant flow restriction.

Silicon, correct me if I'm wrong but in any A/C system, there is hot and there is cold. You just simply can't have the cold without the heat. The condensor heats up when the refridgerant liquifies, and the evaporator cools down when the refridgerant turn to a gas. When overfilling occurs the refridgerant can't change phase as easily and then you don't get as cool of air as you should. But shouldn't that work both ways? The evaporator doesn't get as cold as it should normally, so theoretically shouldn't the condensor not heat up as much as it normally would as well?

[silicon212]

You're right in the respect that as the A/C is doing its thing, it will force hot air through the radiator as opposed to 'clean' air. In the design of the cooling system, this is accounted for (all else being equal), so it will not lead to overheating in any other than the absolute worst conditions (stuck in traffic on a freeway jam somewhere HOT, such as Blythe or Death Valley). If the A/C is overcharged, it 1) works the compressor harder, using more power and indirectly generating more heat, and 2) the condenser will run even hotter, overloading the cooling system. The air coming from the A/C vents will also be warmer as the hot refrigerant will not properly boil out in the evaporator (line pressure too high).

FWIW, here in hot, sunny Mesa AZ, my engine temperature generally runs in the 220-230 range. It matters not whether the A/C is on or not. In the winter, peak temperatures will drop down to 200-210, seldom below. This is optimal operating temperature (although 230 is kinda warm, it's been like that for the 5 years I've had the car).

[PeteA216]

A few years back, on New Years eve the upper radiator hose on my 1989 GMC Sierra blew and obvously after loosing cooland the engine began to heat up. When the guage reached the 240 mark the "Idiot" light came on saying "TEMP" in red. Does that mean you're engine is running close to the danger point?

[silicon212]

When the cooling system is pressurized, and with the proper amount of coolant mixed, boil temperature is in the 245 range. The light should come on right before, or at the beginning of the boil phase.

With my car in the heat down here, I have to run 89 octane gasoline to prevent detonation while driving, due to the 230 temperature, but it still hasn't overheated.

[PeteA216]

couldn't you just run a cooler thermostat to bring the tempurature down so you can run regular gasoline and not run so close to the boiling point?

[redrddvl]

i found out theres a leak in the compressor.and theres no anti freeze in the tank

[silicon212]

Originally Posted by PeteA216

couldn't you just run a cooler thermostat to bring the tempurature down so you can run regular gasoline and not run so close to the boiling point?

No. The system has a 195 degree thermostat in it, because that's the temps at which the engine has its best performance and gets its best economy. Besides, peak temperatures are going to be as high regardless.

Plus, the engine has nearly 9:1 compression ratio with iron heads, ergo the 89 octane. I get away with 87 in the cooler months.