What is this connection for - The 1947 - Present Chevrolet & GMC Truck Message Board Network

seattle gmc · 07-19-2020, 08:10 PM

I recently just purchased a pretty decent 1990 gmc k2500. And I'm trying to fix my a/c system.

Trying to figure out what this green connection is for on the back of the ac compressor? And where the wire that use to go to it, might be routed. This is the third motor that has been placed onto the vehicle, and it's hard to know what is missing.

EVRLET · 07-20-2020, 03:21 AM

That is the ac high pressure cutout switch, one wire. Maybe a green wire with black connector. It’s bundled in the engine wiring harness.

seattle gmc · 07-20-2020, 10:42 PM

Thanks for the reply. Unfortunately I spent the evening looking for that wire but could not find it. I opened up most of the looms hoping it was folded over in one of them but never found it. My AC is running, but I'm not sure it's good to use it without that wire hooked up?

Kudzupatch · 07-23-2020, 10:20 AM

No expert but lots of older cars never had a high pressure switch. I am not sure if my 93 does either. I just check it with the gauges, with it working and as long as they are right I don't think I would worry to much about. It shouldn't be had to add one in the circuit though.

**hatzie** · 07-23-2020, 08:33 PM

1990 would've been setup for R12 refrigerant. It wouldn't have the wiring for the high pressure cutoff switch. You can look at the wiring diagrams to be sure tho.

That compressor is for an early R134a vehicle 1995 ish. GM stopped using the Harrison R4 compressor after 97 or 98 or so.

seattle gmc · 07-23-2020, 10:02 PM

Thanks for all the replies. You can't see it in the picture. But that yellow tag, says caution r12 refrigerant under high pressure. I went on ebay and got a few cans of r12 and charged the system. and got it working, the compressor seems to cycle on and off continously, with no break. kind of bothering because you can feel a huge lag on the engine at highway speed.

**hatzie** · 07-23-2020, 10:20 PM

I assume you pulled a vacuum on the system to check for leaks before charging it up.
Just filling it up when the system has leaked out and filled with air is not good for your compressor.

Cycling on and off could be several issues.
Put a gauge set on it and make sure you have a full charge and haven't overfilled the system.

seattle gmc · 07-27-2020, 11:38 PM

Quote:

Originally Posted by hatzie

I assume you pulled a vacuum on the system to check for leaks before charging it up.
Just filling it up when the system has leaked out and filled with air is not good for your compressor.

Cycling on and off could be several issues.
Put a gauge set on it and make sure you have a full charge and haven't overfilled the system.

No I didn't. The system still was holding pressure and working kind of. Slighty cold air would blow when the ac was turned on. What your suggesting would have been the proper thing to do. I should maybe start a new thread, with the back story since I did figure out what that connection is for.

LT7A · 08-03-2020, 05:41 PM

Whether you start a new thread or just continue this one it sounds like it would be good info to have. BTW, howdy neighbor.

07-19-2020, 08:10 PM	#1
seattle gmc Registered User Join Date: Dec 2013 Location: Seattle, WA Posts: 155	What is this connection for I recently just purchased a pretty decent 1990 gmc k2500. And I'm trying to fix my a/c system. Trying to figure out what this green connection is for on the back of the ac compressor? And where the wire that use to go to it, might be routed. This is the third motor that has been placed onto the vehicle, and it's hard to know what is missing. Attached Images __________________ 1970 GMC K2500 aka MaTeR 2007 Chevy Silverado 1500HD Classic

07-20-2020, 03:21 AM	#2
EVRLET Registered User Join Date: Aug 2015 Location: Las Vegas NV Posts: 354	Re: What is this connection for That is the ac high pressure cutout switch, one wire. Maybe a green wire with black connector. It’s bundled in the engine wiring harness. __________________ Customization is what you want it to look like -- not what other people think it should look like

07-20-2020, 10:42 PM	#3
seattle gmc Registered User Join Date: Dec 2013 Location: Seattle, WA Posts: 155	Re: What is this connection for Thanks for the reply. Unfortunately I spent the evening looking for that wire but could not find it. I opened up most of the looms hoping it was folded over in one of them but never found it. My AC is running, but I'm not sure it's good to use it without that wire hooked up? __________________ 1970 GMC K2500 aka MaTeR 2007 Chevy Silverado 1500HD Classic

07-23-2020, 10:20 AM	#4
Kudzupatch Registered User Join Date: Apr 2013 Location: GUNTERSVILLE Posts: 621	Re: What is this connection for No expert but lots of older cars never had a high pressure switch. I am not sure if my 93 does either. I just check it with the gauges, with it working and as long as they are right I don't think I would worry to much about. It shouldn't be had to add one in the circuit though. Last edited by Kudzupatch; 07-24-2020 at 08:16 PM. Reason: Pain killer induced typos

07-23-2020, 08:33 PM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,912	Re: What is this connection for 1990 would've been setup for R12 refrigerant. It wouldn't have the wiring for the high pressure cutoff switch. You can look at the wiring diagrams to be sure tho. That compressor is for an early R134a vehicle 1995 ish. GM stopped using the Harrison R4 compressor after 97 or 98 or so. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

07-23-2020, 10:02 PM	#6
seattle gmc Registered User Join Date: Dec 2013 Location: Seattle, WA Posts: 155	Re: What is this connection for Thanks for all the replies. You can't see it in the picture. But that yellow tag, says caution r12 refrigerant under high pressure. I went on ebay and got a few cans of r12 and charged the system. and got it working, the compressor seems to cycle on and off continously, with no break. kind of bothering because you can feel a huge lag on the engine at highway speed. __________________ 1970 GMC K2500 aka MaTeR 2007 Chevy Silverado 1500HD Classic

07-23-2020, 10:20 PM	#7
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,912	Re: What is this connection for I assume you pulled a vacuum on the system to check for leaks before charging it up. Just filling it up when the system has leaked out and filled with air is not good for your compressor. Cycling on and off could be several issues. Put a gauge set on it and make sure you have a full charge and haven't overfilled the system. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

08-03-2020, 05:41 PM	#9
LT7A Registered User Join Date: Oct 2015 Location: PNW Posts: 3,496	Re: What is this connection for Whether you start a new thread or just continue this one it sounds like it would be good info to have. BTW, howdy neighbor.

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