98 Buick Park Avenue, AC low pressure too high

[shrydvd]

1998 Buick Park Avenue Ultra

Issue started with no cold air. In the past year I have had issues with that & have added stop leak and freon. A couple times I again added freon when it would start not working again. The last time, was several months ago & it has held quite well.

I thought I needed to add freon again but when I put the Walmart gauge on, it showed in the red.

From there I have tried the following:
I went to AutoZone & got a manifold gauge set. Both high & low pressure registered about 88 psi (static). I honestly don't remember what it was with the AC on.

I went back to AutoZone & got a vacuum pump. My thought was that maybe all the crap I was putting in there in the past caught up to me. So, I ran it down to -27. I had bought 3 cans of freon & one 8 oz bottle of PAG 150 oil (book called for 36 oz freon & 8 oz of the PAG 150 oil).

I read how to put the middle (yellow) line in the bottle of oil & open the high side valve to suck the oil into the system, which I did. Then, using my Walmart gauge again, I started to add the freon but it again went into the red.

Observations & things I have tried (besides the above) are:
1. The clutch does not kick in.
2. I shorted the relay which did cause the clutch to kick in.
3. I measured the voltage on the connector to the compressor & it showed something like .4 volts? I thought this was the problem until I jumped the relay & it worked.
4. An issue I keep seeing come up is the low pressure switch. The trouble is, I can't seem to find that. There are multiple places that tell where it is, but I must be completely blind because I can't find it.
5. I also removed (will buy new ones tomorrow) the cabin filters & my goodness, those things were disgusting.
6. I checked all the fuses.

My question then is, does all of this sound like it could be the low pressure switch? If so, can someone please send me a picture or something that will tell me where it is on this vehicle?

Thank you all in advance for any guidance and/or help you can give me.

[GM Tech]

There is NO low pressure switch on your 1998 vehicle!!!! Low pressure switches stopped on "C/H" cars in 1996! which used an HD-6 compressor. 1996+ MY "C/H" cars utilizes a V-5 variable stroke compressor- that averts evaporator freeze-up by destroking the displacement. You have a high side pressure transducer- 3 wire (not a switch!) on the discharge line just beyond the compressor that tells the fan(s) when to come on and shuts the compressor off if the system pressure is less than 47 psi (low charge protection that disables the compressor) or above 425 psi. So if system pressure is greater than 47 psi and compressor does not come on by itself, then you have an electrical issue- perhaps the wires are broken att he high side pressure transducer, or the transducer itself is bad. NEVER try to jumper a pressure transducer- you can tell if it a transducer- because they all use three wires, not two like a switch.

You have eliminated half of the problem by jumping across the relay terminal and have a positive engagement- so now you know that the ecm is keeping the relay from energizing due to it's thoughts- it can disable a/c for many reasons- such as high or low pressure, or extremely high engine temperture- like 242 or greater- does your temperature sensor for the ecm work? What does you scan tool say that the engine coolant temp is? do you have coolant temp codes set in your service engine light?

[Cusser]

In the past year I have had issues with that & have added stop leak and freon.

Stop leak is a real crap shoot !!! Not recommended at all !

[shrydvd]

There is NO low pressure switch on your 1998 vehicle!!!! Low pressure switches stopped on "C/H" cars in 1996!

Well THAT explains a lot. I seriously thought I was blind or something!

You have a high side pressure transducer- 3 wire (not a switch!) on the discharge line just beyond the compressor that tells the fan(s)

I'll look for that this weekend. I think I did read something about this but had that danged low pressure switch in my head.

You have eliminated half of the problem by jumping across the relay terminal and have a positive engagement- so now you know that the ecm is keeping the relay from energizing due to it's thoughts- it can disable a/c for many reasons- such as high or low pressure, or extremely high engine temperture- like 242 or greater- does your temperature sensor for the ecm work?

temperature sensor seems to be working OK. Dashboard shows it rising to normal operating temp, etc.

What does you scan tool say that the engine coolant temp is?

Not sure, I don't have a scan tool.

do you have coolant temp codes set in your service engine light?

Haven't had any engine lights come on. That's the main reason I didn't get the code reader at Autozone. I didn't think it would help since there were no check engine lights.
You have given me some things to look at, especially that transducer. I'll definitely look at that & get back with you.
I really appreciate you taking the time to help, GM Tech!

[shrydvd]

Stop leak is a real crap shoot !!! Not recommended at all !

Yeah, I knew I would catch flack for that one but I was desperate