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Discussion Starter · #1 ·
First off, could someone confirm that there is indeed supposed to be a switch on the back of the AC compressor?

If so, I have to admit to making a fairly significant error. I disposed of my old compressor without removing said switch. Does anyone have a part number or could confirm exactly what switch it is? Is that the cycling switch that's indicated in the Haynes diagram?

Secondly, I've installed the new compressor, the system is serviced already. Can I install the switch at the back of the compressor without evacuating the system?

For simplicity sake, the truck is a 97 Silverado K1500 with the 350/5.7.

Thanks in advance for your help!
 

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Did you unhook an electrical connector from the back of the old compressor? If not, it didn't have a switch. If it did have a switch and you had to replace it, you would have to evacuate the system and all to put it in. Some of the compressors had the switch in them and some did not. I don't know specificly if yours did or not.
 

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Discussion Starter · #3 ·
I believe so...but a few weeks lapsed from pulling it apart to putting it together...so it's a little hazy. The fact that I have a plug that I can't find a home for that is switched with the AC button on the dash makes me really believe there was a switch. I've read that some models you could replace the switches without evacuating the system...but couldn't confirm the years.
 

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I have never seen a switch that could be replaced without evacuating the system, considering it is a freon pressure switch and has to be in contact with the freon.
 

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I have no idea what they are talking about. In order for a pressure switch to tell the pressure, it will have to have the presurized freon actually pushing on it.
 

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On the older compressors, some did have a switch in the backside (sometimes 2). Most of the time, it was just a high pressure switch, which is a closed switch unless the pressure in the system goes above a set point where it opens the circuit and causes the compressor's clutch to disengage. They are held in place by a snap ring, but when you buy a new compressor, they come with a plug installed and you have to either install the old switch, buy a new one, or leave that plug in place as the compressors had universal applications and do not always need the switch. The high pressure switch is just a safety device and normally is never needed, however, if your fan stops working or isn't pulling enough CFM's through the condensor, than the system can over pressure and cause damage to the compressor. I know plenty of people who have made your mistake and just left the switch out and used a jumper between the old connector. To install a switch now, you will have to evacuate the system, install the switch and than recharge it.

By the way, my online database is showing that the 97's high pressure cut out switch is located on the compressor and the low pressure switch is on the accumulator.

Oh, and those that are talking about replacing a switch without evacutating are referring to switches that are mounted on the accumulator or lines, as a lot of them use a schrader valve so that the switch can easily be swapped out without removing the refrigerant. When the switch is screwed on, it opens the valve and that's how the switch works.
 

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Discussion Starter · #9 ·
Thank you for the very detailed response!

I think I'm just gonna go ahead and evacuate the system and replace all the switches. Might as well...then every darn AC component has been replaced and I can call it good.

I need to test it by putting a jumper on that plug though...and see if I have any other issues. If I jumper that plug should I get voltage on both lines or does it work by grounding the circuit out to 0?
 

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Discussion Starter · #10 ·
Oh, one other question. If the high and low switches are as you described...what sensor/switch is on the high pressure line just after the manifold at the compressor?
 

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The high pressure switch just grounds out a wire for the Vehicle Control Module is appears on the wiring diagram.

Also, on the diagram, this is what it says there are and where they are located, but it could be wrong. Sometimes the information is spot on and sometimes it's wrong, depends on the vehicle.

Water Valve (Suburban, Utility, Crew Cab Only) --Right Center of Intake Area
A/C Low Pressure Switch -- On top rear of A/C compressor
A/C High Pressure Switch -- On Bottom rear of A/C compressor
A/C Compressor Cycling switch -- On top right of A/C Accumulator
 

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Discussion Starter · #12 ·
Thanks again for the great info! Did that info come from the FSM? I'm more and more convinced I need to buy one, the Haynes stuff will only get you so far...I'd love to find a digital version...but there are so many scams out there that you never know what you're going to end up with.

I'll have to look again, but I'm fairly certain there's only one switch receptacle on the rear of the compressor. The only other switch near the compressor is the one I mentioned that is in the line just on top of the compressor. I'll snag a pic this morning and try to throw it up here. Thanks again!
 

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Discussion Starter · #14 ·
OK, I've attached a picture. The switch I'm wondering about is the one to the right of the intake, left of the red cap on the AC system. Like previously mentioned, there's a switch on the back of the compressor (presumably high pressure cutoff) and a switch on the accumulator (presumably the cycling switch).
 

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You do have a spare connector on the back of the compressor correct?

Do me a favor, when you get time, check the wire colors of the 3 switches, I need to know what colors the wires are for each switch, and then I can compare it to a wiring diagram.

Switch on accumulator
wire 1?
wire 2?

Switch on high side line
wire 1?
wire 2?

Switch on compressor
wire 1?
wire 2?
 

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Discussion Starter · #16 ·
OK, here's what I've got:

Switch on the accumulator: DK GRN & BLK/WHT

Switch on the high side line: DK BLU & BLK/WHT

Switch on the compressor: LT GRN & DK GRN/WHT

The LT GRN line on the switch on the compressor is switched with the AC button on the dash, confirmed. In the other switches the non BLK lines have voltage with the ignition on, as I believe they should.

Thanks again for your help!
 

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Discussion Starter · #17 ·
So, the plot thickens. I jumpered all three switches. Everything worked great. I removed the jumper on the cycling switch, nothing...so the cycling switch is bad. However, I'm going to go ahead and just replace all the switches.

Based on two wiring schematics I have, I can confirm the cycling switch is in fact on the accumulator. No problems.

I have two conflicting diagrams with regards to the High and Low pressure switches. I've also determined that Checker has 3 different low pressure switches, all of which appear to fit into the back of the compressor and fit the plug that was removed from there, and has LT GRN & DK GRN/WHT wire. According to the GM schematic from the dealer for a 98, this should be the High Pressure switch. This line is also switched with the AC button on the dash.

Checker has two different Hi Pressure switches. One that would fit the back of the compressor and one that would fit the supply line on the system. However, the plug that runs to that switch is a DK BLU & BLK/WHT line...which GM says should be the low pressure cutout switch.

The Haynes manual swaps the wires to the high and low switches...which would also be in coincidence with the switch supply at Checker.

Can anyone confirm that the switch on the supply line is in fact the HIGH pressure switch, and the switch on the back of the compressor is actually the LOW pressure switch?

Again the truck is a 97 with the 350.

Thanks for the help!
 

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IP076 said:
Switch on the accumulator: DK GRN & BLK/WHT

Switch on the high side line: DK BLU & BLK/WHT

Switch on the compressor: LT GRN & DK GRN/WHT
Switch on Accumulator: A/C compressor cycling switch

Switch on the high side line: A/C High Pressure Cutout Switch

Switch on the compressor: A/C Low pressure cutout switch

Sorry I wasn't really online much yesterday. I'd go by the wiring colors, not where the diagrams state they should be. And it makes more sense that the high line would have the hi pressure switch since you have a switch on it.

 
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