Low Pressure Switch 94 Firebird AC

[Fly by Night]

I am looking for the AC low pressure switch on a 94 Formula w/350. Normally, I would expect to find it on the low side and it be a two pin. There is a three pin in the smaller return line, just doesn't look like what I what. The goal is to get the compressor to kick on in order to complete an AC recharge. It has a slow leak that we are aware of. Usually can go about 30-45 days before it needs a can. This is the first attempt to fill since October. I show about 130 on the high side gauge today. Any pictures or thoughts appreciated. Thanks.

[formula_gramps]

Fly,

I'm assuming from your post that the problem you have is that you can't get a can of r134 to go into the system, because the low pressure switch is telling the computer to keep the compressor off --- is that correct?

If so, rather than mess with the switch itself, I found it easier to jumper the relay that directs power to the compressor. I wouldn't do this for a long time, and only once you have a can of refrigerant hooked up and ready to go, and only until you've got enough in there to kick the pressure up to the point where the compressor will stay running on its own.

I had this situation on my 94 Formula last year. It had actually not been recharged for 15 years....lol.

If you go to this thread that I put up last year and jump to the second page, towards the end you will see two photos I posted. One showing the relay, and the next showing the two pins to short to make the compressor come on.

check out this thread

As with most threads here, lots of other good information (pressures, etc.) supplied by the good folks here.

Maybe you can even utilize my "microwaved towel" trick when recharging....lol. It worked pretty well for me.

Best of luck!

[Trash man]

not sure if this helps you or not, but heres a diagram off shoebox's site

http://shbox.com/1/hvac_compressor_control.jpg

[Fly by Night]

Gramps and Trashman, thanks for the links. I will read them over and see what I can do. Gramps is correct, I cannot load the R-132 without the compressor running. Getting hot here in AZ! I will post results.

[Injuneer]

Gramps and Trashman, thanks for the links. I will read them over and see what I can do. Gramps is correct, I cannot load the R-132 without the compressor running. Getting hot here in AZ! I will post results.

Your A/C requires R-134A

[bobdec]

fly by nite, just a couple more things.. There is no low pressure switch in these F-fody's the three wire sensor on the high a/c line feeds a 0-5 volt pressure reading to the pcm. If you try to ground any of the wires or short them together you will most likely throw an A/C DTC in the PCM. AND the DTC will prevent the PCM from picking the compressor relay. This confuses many people because after adding r-134 the system still does not work till you reset the error (power off PCM). Just something to keep in mind. To force compressor on use trash man's advice in post #3 & url for reference, pull a/c relay and jump B1 to B4. This jumping may also create a DTC so again reset PCM after any A/C electrical jumping. I personality have seen one 12oz can of R-134 added to a vacuumed empty system provide enough pressure to kick off the compressor, but that may be just a uniqueness of my system.

[Fly by Night]

I am still working it. I will reset the pcm and see if I can clear all the codes. I did ground the three wire switch. (oops) Most likely dumped a code. Thanks

[FTA1995]

I had the same issue when I first got my F body, tried filling the freon to no avail. I had some success after the pump kicked over a few times, eventually got the thing to blow **some** very inefficiently cooled air through for about a month or so, with what sounds like a similar problem. As far as what Fred said about using the proper refrigerant, you really shouldn't use R-132, it contains a mineral oil type lubricant that won't properly cater to the moving parts in the system. Also, the R-132 compound utilizes a marginally heavier compound containing chlorine; it might cool a bit more effectively, but at the cost of a major failure down the line in your system. Take your time, do it right. You will thank yourself for it

[Trash man]

if i remember right when filling a R134a system you want low side between 30-35psi and high side around 150-175psi(with the compressor on)

[Fly by Night]

I am still fighting this battle. I jumped the relay in the main fuse box, etc. I disconnected the battery overnight and did the capacitor drain with a resistor in an attempt to reset the PCM. Still no luck. I can't believe the compressor just up and died. I show pressure in the system. Does anyone know if the I can read the AC error code on an AutoZone ODB reader?

[bobdec]

Doubt you could get the PCM scanned at any parts place. The '94 (and '95 LT1) is ODBI but it's a halfbreed with flash memory. Requires an intelligent programmed scanner to read the flash memory. They will stick an OBD1 scanner on it.. it will light the SES light and start the fans with no communication and they will say your PCM is bad. To prove it's the PCM (DTC error) or compressor clutch you can pull the a/c relay - wrap two 5-6 inch thin gauge wires one around the relay pin B5 the other around pin B4, make sure they do not short to each other or to anything else. Then replug the relay back in. The PCM will ground pin B5 to pick the a/c relay and the relay output +12 on pin B4 picks the clutch. You can use a voltmeter to check for ground from PCM (pick relay) on pin B5 and then +12 to clutch on pin B4. This verifies the PCM and relay are good and the problem is in the clutch or compressor. here is a schematic ref shoebox http://shbox.com/1/hvac_compressor_control.jpg below is an example (not the a/c relay) of how to attach the wires...

[Fly by Night]

Had to take time away from the project

I fell off a scaffolding and been laid up for a bit. Back at this AC issue, my wiring basics worked out as suggested and I still cannot get the compressor to engage. So far I have not found a OBD1 scanner capable of probing the flash memory codes. I am not looking forward to digging into the frontend to access the compressor for a closer look. Any one have tips or tricks to get at easily?

Thanks, FBNE

[bobdec]

With engine off pull the a/c relay and jump +12 v to relay board pin B4 (a/c clutch pick) you should hear the a/c clutch click on and off while touching the jumper to pin B4. If that does not work clutch winding is bad, wire from relay board to clutch is open or connector on clutch is defective. If clutch clicks on then start engine and repeat to see if compressor spins, if not clutch plate is burnt out. No easy way to get at compressor.. love these F-Body's