High pressure A/C switch on a 92?

[682XLR8]

I'm currently researching and gathering parts for rebuilding the A/C system on my 92 C1500 5.7. I will document that in another thread. In all the searches I've done and threads I've read, I keep seeing references to a high pressure switch mounted on the back of the compressor. Looks like some trucks have this switch, and some don't. The previous owner had the system redone for r134a with an R4 compressor from Compressor Works I think it was, this compressor doesn't have this switch, and I can't find any evidence that it ever did from digging into the wire loom (maybe I didn't dig deep enough), but then again, who knows what they did to get the ac working.
So my question is....did the 92 come with this switch, and if not, should one be fitted?

 

[PlayingWithTBI]

So my question is....did the 92 come with this switch, and if not, should one be fitted?

Does your 92 have the "recirc" button on the controls? If not there was a one wire high pressure switch that would close the fresh air damper to help lower high pressures (IMO totally useless). If it does have that button then it should have a 2 wire high pressure switch (on <200, off >430 PSI) that is either wired in series with the low pressure cycling switch or goes directly back to the controls to shut off the compressor when you get too high pressure so you don't blow it up or blow out seals. This switch should work on your R4 compressor.

https://www.oreillyauto.com/detail/...-c1500-pickup-rwd?q=a/c+pressure+switch&pos=1

 

[682XLR8]

Thanks for the fast reply!
No recirc button, but there is a "MAX" button between the A/C and OFF buttons, would this require a switch to be added?

 

[PlayingWithTBI]

No recirc button, but there is a "MAX" button between the A/C and OFF buttons, would this require a switch to be added?

Yes that's it. I just used the wrong description. Max/Recirc essentially do the same thing. The older years (88 - 90maybe?) didn't have that, they had a timer where, if you were on the coldest setting and the fan on 2 or 3, the recirc door would open after 30 seconds.

Yes, you need a high pressure switch and you need to find where the wires that went to it are hiding. I would guess someone just connected them together to bypass that switch and maybe hid them in the loom?

You can look up the wiring on your 93 here.
https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[682XLR8]

Thanks for the link to the PDF manuals, had no idea they were on this site. They will be very helpful!
I looked at the wiring manual for 1992, page 159 mentions an AC compressor switch located on the HP line, with a diagram on page 259 figure 40, but the HP switch is not shown, nor is it shown on the wiring diagram on page 166
Is the manual wrong or am I not looking in the right place?

 

[PlayingWithTBI]

I looked at the wiring manual for 1992, page 159 mentions an AC compressor switch located on the HP line, with a diagram on page 259 figure 40, but the HP switch is not shown, nor is it shown on the wiring diagram on page 166
Is the manual wrong or am I not looking in the right place?

Yeah, I don't see it on 1992 or 1993 manuals either. Hmmm - maybe wrong? IDK. Other A/C systems have the HP switch in the HP line going from the compressor to the condenser or between the condenser and the orifice tube (after that it becomes the LP side). Maybe someone who has a 92 or 93 can chime in?

 

[682XLR8]

I'd like to hear from someone with a similar year as well
I'll re-check the wiring on my 92 tonight when I get home and post up what I find

 

[someotherguy]

It varies over the years and I wish I could remember all the details. I've battled the same question when swapping parts around rebuilding trucks or parting out others - some compressors had the switch, others have a metal slug filler plug in them, and of course there are a couple different pressure ratings for the switches.

I *thought* my '92 had the switch because when I swapped in an engine from an older truck ('90 I believe was my last donor for the '92) I had to pull the slug out and figure out which switch to buy. <-- DISCLAIMER this is literally 16 years past fuzzy memory here.

Richard

 

[PlayingWithTBI]

I looked at the 1992 Service Driveability and Emissions Manual. In section 1B-4 it says the compressor has a pressure relief valve instead of a high pressure shutoff switch which is supposed to open to atmosphere when pressure gets above 440 PSI (see red arrow). I would not depend on it, if there's still one on the replacement compressor. I know my NAPA new replacement didn't have 1 or it didn't work because it blew out the pressure switch (sounded like a shotgun going off) and tore out the groove for the snap ring holding the HP switch in. I now have the switch I posted above in my new AC Delco compressor and wired it in series with the LP cycling switch - been working fine ever since! YMMV

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[682XLR8]

It varies over the years and I wish I could remember all the details. I've battled the same question when swapping parts around rebuilding trucks or parting out others - some compressors had the switch, others have a metal slug filler plug in them, and of course there are a couple different pressure ratings for the switches.

I *thought* my '92 had the switch because when I swapped in an engine from an older truck ('90 I believe was my last donor for the '92) I had to pull the slug out and figure out which switch to buy. <-- DISCLAIMER this is literally 16 years past fuzzy memory here.

Richard

I have the new (not rebuilt) AC Delco compressor from Summit, and it has the snap ring/slug set-up, I'll post up a pic when I get home