Ac Compressor Switch

Cook_k2500 · Jul 6, 2024

Was replacing my AC compressor and came by a 2 pin switch on the back of the compressor, ended up destroying this switch and was wondering if anyone has any insight on what this switch is. Was told many things and can’t find much online. Assuming it may be a high pressure cutout switch. But again not much confirmation.

1998_K1500_Sub · Jul 6, 2024

Cook_k2500 said:
Was replacing my AC compressor and came by a 2 pin switch on the back of the compressor, ended up destroying this switch and was wondering if anyone has any insight on what this switch is. Was told many things and can’t find much online. Assuming it may be a high pressure cutout switch. But again not much confirmation.

Yes, it's a high-pressure cut-out. It disallows the clutch to engage if the high-side pressure exceeds something like 450psi. These details are mentioned in the factory service manual (see attached, from 1998).

Yours is evidently a 1996+ model, so there is likely another "high-pressure" switch on the manifold but it has a different purpose (see attached, from 1998).

Factory service manuals can be found in .pdf form, here:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Supercharged111 · Jul 6, 2024

1998_K1500_Sub said:
Yes, it's a high-pressure cut-out. It disallows the clutch to engage if the high-side pressure exceeds something like 450psi. These details are mentioned in the factory service manual.

There is another "high-pressure" switch on the manifold but it has a different purpose.

I believe there are a few different high pressure switches in existence, each actuate at a different pressure. No idea the rhyme or reason to that. You'd think the limit is the limit.

1998_K1500_Sub · Jul 6, 2024

Supercharged111 said:
I believe there are a few different high pressure switches in existence, each actuate at a different pressure. No idea the rhyme or reason to that. You'd think the limit is the limit.

Yes, I think I've seen different switches used on the back of the compressors for high-pressure cut-out. I'm not sure the R12 systems even had one, I think they appeared with the deployment of R134a (?) w/ the R4 compressor.

In 1998 and I assume all similar GMT400s, another high-pressure switch resides on the manifold and triggers the HVAC system to enter recirc mode; this also enables the "heater core coolant bypass valve" on GMT400s so equipped.

It'll also enable the aux cooling fan, if so equipped.

This operation is NOT uniform all GMT400s, it changed from year to year, although I suspect from 1996+ it's common.

Cook_k2500 · Jul 6, 2024

1998_K1500_Sub said:
Yes, I think I've seen different switches used on the back of the compressors for high-pressure cut-out. I'm not sure the R12 systems even had one, I think they appeared with the deployment of R134a (?) w/ the R4 compressor.

In 1998 and I assume all similar GMT400s, another high-pressure switch resides on the manifold and triggers the HVAC system to enter recirc mode.

It'll also enable the aux cooling fan, if so equipped.

This operation is NOT uniform all GMT400s, it changed from year to year, although I suspect from 1996+ it's common.

sounds good thanks for the help

Supercharged111 · Jul 6, 2024

1998_K1500_Sub said:
Yes, I think I've seen different switches used on the back of the compressors for high-pressure cut-out. I'm not sure the R12 systems even had one, I think they appeared with the deployment of R134a (?) w/ the R4 compressor.

In 1998 and I assume all similar GMT400s, another high-pressure switch resides on the manifold and triggers the HVAC system to enter recirc mode; this also enables the "heater core coolant bypass valve" on GMT400s so equipped.

It'll also enable the aux cooling fan, if so equipped.

This operation is NOT uniform all GMT400s, it changed from year to year, although I suspect from 1996+ it's common.

With the R12 stuff, whether or not you had a high pressure switch also depended on whether or not you had a recirc function.

GoToGuy · Jul 6, 2024

Did you remove the snap ring ? Replace with same color switch, in normal practice.

Cook_k2500 · Jul 6, 2024

GoToGuy said:
Did you remove the snap ring ? Replace with same color switch, in normal practice.

Removed the snap ring, switch still wouldn’t come out. Currently trying to look for a new one.

PlayingWithTBI · Jul 6, 2024

Supercharged111 said:
With the R12 stuff, whether or not you had a high pressure switch also depended on whether or not you had a recirc function.

Yes, the systems without the RECIRC or MAX button still had a one wire high pressure switch that controlled the fresh air door. When it saw high pressures, it would close the door so you get as much hot air coming in to defrost the evaporator. GM has long since discontinued that switch but, you need to ground the wire going there so, the air door will open (after 30 seconds) when you have the A/C on, temperature on coldest, and fan switch on 2 or 3.

GoToGuy · Jul 6, 2024

Has oring seal on base. After removing the snap if you can't finesse it out, it a pressure switch, monitors pump pressure. If you apply some compressed air to the pump and gently increase the case pressure, while holding rag over switch to catch it and any oil. Just don't shotgun it out like slug. Eye protection , the usual smarts.

Ac Compressor Switch

Cook_k2500

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1998_K1500_Sub

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88-98 Service Manuals

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Supercharged111

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1998_K1500_Sub

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Cook_k2500

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Supercharged111

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GoToGuy

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Cook_k2500

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PlayingWithTBI

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