Yet Another A/C issue....

[frotosride]

Does anyone know if the factory a/c compressor has somekind of a relief on the compressor it's self?  I ask this because I have had what seems to be a relief valve opening on the compressor twice in the last month. they were both under the same curcumstances with the truck parted and the A/C running. I have not seen it at all when driving so I'm curiouse. Even though this has happened a few times I haven't noticed any effect on my A/C's ability to cool the cab. It is a r-134a convert....

Thanks in advance.

[frotosride]

Ok so I figured out the answer to my question and I am not supprised to learn that ust like the refrigerant systems I work on the ac delco and most every other compressor has a relief valve in the system in some way. Not I know there are many reasons wht my relief can be lifting like the expantion tube clogging/condensor clogging or any number of things within the system. Does anyone here know of any common problems that may cause high discharge pressures such that the relief valve lifts?

[frotosride]

Possible cause..tell me what you think... IS it possible that, even thought the truck hadn't warmed up at all, The discharge pressure spiked because lack of air flow accross the condensor?. I only ask this because I had to disconnect the signal wire to the fan because everytime the fan came on it would send signal power to the clutch and thus engage the compressor. Just a thought because i know that it is a possibility.

[markus]

so you have an electric fan?

let me get this right, you disconnected the fan power (or signal) and then the a/c relieved? that would be a definite cause, since there wouldn't be any airflow through the condenser.

don't get confused on this, the a/c is an independent system from the engine cooling system, but since it makes sense to use the fan of the cooling system to also cool the condenser it is built like that in any car i know. but still, the fan has to work for the a/c system, if not, your pressures get too high and relieving might happen (normally at 400 to 450 psi).

so don't just disconnect your fan, nothing to do with your truck warmed up or not, the a/c needs it...

[454Man]

I am epa certified. Not that it matters, but id say the relief spring is weak or the system is overcharged. 134 will have higher head/ high side pressure readings than r12. But if it was the orifice tube it would happen soon as the compressor cut on.

[bd]

Possible cause..tell me what you think... IS it possible that, even thought the truck hadn't warmed up at all, The discharge pressure spiked because lack of air flow accross the condensor?. I only ask this because I had to disconnect the signal wire to the fan because everytime the fan came on it would send signal power to the clutch and thus engage the compressor. Just a thought because i know that it is a possibility.

If I'm duplicating your problem, and the compressor runs everytime the engine fan turns on (even when the A/C and defrost are turned off), then you need to insert a high pressure switch and relay between the engine cooling fan and the compressor clutch to isolate them electrically - your compressor is backfeeding from the fan circuit.  If you already have a relay controlling the engine fan, then you can tie the pressure switch into the control circuit of the existing relay.

[frotosride]

Thanks for the help guys. I figured out the problem. It is the lack of my fans coming on with the A/C. Without the cooling in the condensor the heat from compression raises rapidly thus causing the pressure to rise exponentially. I knew that the A/c needed that cooling but I didn't realize that without the heat transfer,the pressure would build so quickly. I figured all this out while I had time to sit with "old Blue" from 530am this morning til about an hour ago....it wasn't a planned event but my starter silenoid went out and due to my over torquing ability I killed the side post on my battery. At least I got a new starter out of the deal but I have to say the one from '87 held it's own for longer than I'd ever expect it to.
I also learned how intolerable the ecm is to low battery voltage..she doesn't like it much at all. Once again Thanks guys. I'm going to hook the remote switch back up and hope I didn't loose too much freon. Anyone know what pressures i should have either running or off for a fully charged r134a system?

[markus]

should be around 25 to 35 psi low side and 150 to 200 psi high side. for me the best method to figure out is combining a reasonable pressure reading with lowest temp of blown air into the cabin. takes a little more time to do it that way, but sure is what you wanna have. don't forget to measure at around 1500 rpm, not idle.

[frotosride]

Thanks for the info Markus