97' A/C Question

[schmitty850]

i tried my a/c for the first time this year...no cool air. the compressor doesn't even engaged when i push the a/c button. all fuses/relays seem to be okay.

is there a low pressure switch that would prevent the compressor from engaging?

any thoughts?????

thanks
schmitty

[kingarthur2]

Yes . If the AC system is down on pressure and/or empty the compressor will not engage.

Have the system tested to see if any pressure is in the system and if so you may only require a re-gas. If no pressure then the system has a leak or has been discharged at some point.

Prime targets for leaks are:

Compressor shaft seal.

Condensor damage from stones etc.

Corroded alloy pipe work.

The low pressure switch would be my last suspect.

[schmitty850]

thanks for the info.......i understood that the compressor needs to be running to re-charge the system.
schmitty

[kingarthur2]

Originally Posted by schmitty850

thanks for the info.......i understood that the compressor needs to be running to re-charge the system.
schmitty

The AC system can be re-charged with liquid R134a through the high side port very quickly without the engine / compressor running, in fact DO NOT Start engine / compressor when re-charging with liquid refrigerants. You need a set of electronic scales to measure the exact amount of refrigerant .

Re-charging with R134a vapour through the low side port requires the engine / compressor to run and thus "suck " the refrigerant into the system.

[schmitty850]

Okay...if i can get my hnads on a scale...how much?

Or can i jump(and how) the presuure switch and go off the low side?

schmitty850

[LMP]

If at normal operating temperature the pressure switch prevents operation, then it means the system is empty. Pressure with saturated gaz does not depend on the amount of liquid present but only that there exist a saturated state, that is just some liquid - even one drop - and the rest is gas, which is a saturated state. Not having pressure means not one drop in liquid form remains in the system.
This being said, it means if you can procure refrigerant in cans containing a known quantity, then emptying the cans tells how much refrigerant you get into the system. YOur specs normally tell the amount. For my "93, it is 2.62 lb for front only a/c. or 3.50 lb for dual front and rear a/c. If this is same size as R-12 cans I used to use in the past, it will need 3 or 4 cans.
To bypass the switch, just remove connector and jump connector prongs.
IN fact, you can get all refrigerant from the can into the system without engine running (GM procedure is with engine off) if engine and all surroundings is cold, and you just keep the refrigerant can in a warm to moderately hot pail of water. THis establishes the can at a higher pressure than the system and it will empty completely at the pressure of the system. THe higher temperature of water will not generate more pressure: it will just evaporate more quickly out of the can and recondense in the car system.. YOu will be surprised at the amount of heat sucked from the water by the evaporating refrigerant. YOu will need to renew the water several times.

ALso, in a system that would have been opened, evacuation with a vacuum pump would be mandatory before replenishing. If the system just leaked out, it may have stopped at the point where gas pressure inside is equal to atmospheric pressure...but a long winter may have shrinked the gas inside then pull air from the atmosphere......so some air may be present in the system, which is detrimental to proper refrigeration cycle.

[cdru]

The AC system is a sealed system. The refridgerent doesn't leak out on it's own. If you have lost pressure, find out where the leak is and fix it first. It's better for the enviroment and cheaper on your wallet.