A/c compressor wiring

[Crowebar]

I've been a long time lurker first time poster .I'm in the middle of restoring my ac system that was removed from the truck when I bought it and I've hit a speed bump.my truck is a 1988 suburban 1/2 ton 4x4 it has a newer crate motor and rebuilt 700 r4.i can't find the a/c compressor plug anywhere My question is can I jump power to the compressor from the high pressure switch on the accumulator ?? The schematics shows the powers coming from the same place I think if I'm reading it right. I'm ready to charge up just this holding me back.

 

[oneluckypops]

I've been a long time lurker first time poster .I'm in the middle of restoring my ac system that was removed from the truck when I bought it and I've hit a speed bump.my truck is a 1988 suburban 1/2 ton 4x4 it has a newer crate motor and rebuilt 700 r4.i can't find the a/c compressor plug anywhere My question is can I jump power to the compressor from the high pressure switch on the accumulator ?? The schematics shows the powers coming from the same place I think if I'm reading it right. I'm ready to charge up just this holding me back.

You are partially correct. The switch on the receiver dryer is where the compressor receives its signal. But it is NOT a high pressure switch, instead it is the low pressure switch (aka cycling switch). I wouldn't use the word "jumper" when your dealing with A/C. If the pigtail on the cycling switch is present, follow the harness until you find the compressor plug, or you find where it has been cut off, then splice in to the harness and continue the circuit to the compressor.

I not truing to insult your intelligence, but a quick question before you charge your system. Have you vacuumed your system down completely for at least 45 minutes? Failure to do so will cause 2 things, First it will cause your system to have air and moisture trapped in it. It will also cause you to NOT be able to fully charge your system.

I hope your not planning on charging your system with "suicide cans" (Freon cans with a little charge indicator and fill hose built it). You need to have a quality set of gauges hooked up while charging and vacuuming.

 

[chengny]

Yes. Schematically speaking, that is how the power to the compressor clutch is normally controlled.

When the pressure in the low side hits the high set point the contacts in the switch close and power is applied directly to the electro-magnet in the clutch. The clutch then engages the compressor and the compressor starts pumping refrigerant.

As the cabin cools off, the pressure in the low side falls. When the low set point is hit, the contacts open, the clutch is de-energized and the compressor stops.

So, you would not really even be jumping anything - you'd be exactly replicating the factory wiring. The only difference would be that you'd have a new wire between the switch and compressor clutch.

BTW - it's actually a called low pressure control switch, and it's function is to cycle the compressor on/off under normal operating conditions. If you had a high pressure "safety switch" it would be located on the compressor casing. That switch would only operate if compressor discharge head reached dangerously high levels. Most R-4 compressor do not have that switch.

 

[Crowebar]

Thanks fellers I thought that's how it worked I just wasn't sure what the swith was called. And yes I absolutely plan on vacuuming the system I wouldn't want have to go through all this again. Thanks again.

 

[chengny]

If that is a dual A/C system the charge is 84 ounces = 7 X 12 oz cans. But that was for R-12.

When using 134a the charge is reduced to 75 - 90 % of the R-12 capacity. Here is the EPA guideline for 134a in a system originally designed for R-12:

8.The retrofit will generally require an R-134a charge that is equal in weight (# of ounces) to between 75 and 90% of the original R-12 charge. Start with an R-134a charge that is equivalent to 75% of the recommended R-12 charge. If there is excessive clutch cycling, add up to 5% increments of R-134a. Do not exceed 90%.

If yours is only a front system, the charge for R-12 was 44 ounces.

 

[350runner]

I once had a suicide can gauge blew off. Bish shot off like a rocket!

 

[Crowebar]

Thanks Chengny. It is a front and rear system. So far I've replaced the accumulator,new orfice tube,rebuilt compressor from advanced auto, all the orings except the ones on the back under the body I'm not sure I wanna risk taking those apart unless it leaks there. I also replaced the rear expansion valve. I've figured it would take 4.2 lbs of r134a, that's 80 percent of 5.25. I also added pag 46 oil in their appropriate amounts to the system after I flushed it. The r134 conversion has been done to this truck at some time before I got because it's got the conversion fittings. Gonna have vac pulled Thursday and add the freon. By the way I bought the 20 dollar tap kit with gauge from advanced.

 

[Crowebar]

This web site is a wealth of knowledge I've consulted previous post on here to get me as far as I am.

 

[chengny]

Factory spec charge for a Suburban with front and rear system = 84 oz (R-12)

84 (R-12) X .8 = 67 oz (134a)

67 / 12 (oz per can) = 5.6 cans of 134a to charge a dual system Suburban