87 ls swap a/c system wiring

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RummedMonkey

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colby
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Hey guys, first time poster. I have a 1987 c10 with the ls swap. I am stuck on the wiring. The light green wire going to the low pressure switch is hooked up and receives a/c request. The dark green wire is not hooked up and I'm not sure where it needs to go. The high pressure switch on the back of the compressor- the ground is hooked up. The power wire is not connected. If I tie the high pressure 12v wire to the low pressure 12v wire I can get the compressor to come on but does not cycle in stages. Im sure that is not the correct way of connecting the wires so I disconnected the wire going to the compressor. Any help will be appreciated. So I am needing to know where the dark green wire on the low pressure switch @ dryer goes and also the 12v high pressure on switch wire on compressor goes.
Am I missing just a relay? Do I need to wire a/c request to relay-then term30+85 relay then 86term to low pressure switch- wire high pressure 12v to term 87 relay? If so does the ecm detect wot shut off?
 
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Charlie

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:welcome:
 

73c20jim

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Check out the wiring diagrams in the reference section.
 

yevgenievich

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Need a bit more info. What compressor, is it only coil connector on it or actual high pressure switch and if you want to let the ls computer controlled. If you skip computer control and using stock system without high pressure switch then the request from the cab does go to low pressure switch, then from it straight to the coil on the compressor. Other side of the coil goes to ground. If there is a high pressure switch then run power through it. First low pressure, then high pressure, then coil.
For ls computer control you would run from low pressure switch to ecm request ac pin. Then ac engage pin from ecm to ground side of a relay that would then feed the coil on the compressor. Ls style pressure sensor should be wired in for it to know pressure. Without pressure sensor connected it will think no Freon and act as low pressure interlock.
 

Camar068

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I thought there was only one signal from the vehicle that went to ECM to tell it that AC was on....and to increase the idle a bit. I'll try to dig it up tomorrow as I'll need to know the same info when I get my AC hooked up.
 

chengny

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1. So I am needing to know where the dark green wire on the low pressure switch @ dryer goes and also the 12v high pressure on switch wire on compressor goes.

2. Am I missing just a relay?

3. Do I need to wire a/c request to relay-then term30+85 relay then 86term to low pressure switch- wire high pressure 12v to term 87 relay?

4. If so does the ecm detect wot shut off?



1. They are connected together at the firewall - near the junction block. The connector style makes them unmistakable (see below)

2. There is no relay involved in the compressor control circuit

3. No

4. The ECM will receive an input signal that the compressor is engaged using just the factory wiring harness.


From low side switch:

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To compressor clutch:

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Another image of the control switch side of the connector


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A schematic view of the circuit - while your connector may not look like this, the wiring goes to (and comes from) the same places:

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yevgenievich

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On tbi trucks it is just ac is on signal, on some ls computers it does the control of the ac and fans according to the pressure sensor that allows to indicate low/high and in between pressures
I thought there was only one signal from the vehicle that went to ECM to tell it that AC was on....and to increase the idle a bit. I'll try to dig it up tomorrow as I'll need to know the same info when I get my AC hooked up.
 

Oldmanyoungertrk

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Bringing Older post back to the top, Any new clarification on wiring a 2001 Silverado LS 5.3 compressor, Lt blue wire and green wire w/white stripe on back of the compressor, is this the high pressure switch? I would prefer to use the 1 request wire from the ecm to I sure safe operation.
 

wv79k10

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Need some clarification on this myself....2000 lq4 with factory compressor going in a 79 k10 factory air truck.......what needs to be wired to the ECM? And to power the compressor its just the dark green wire to power side of compressor and the other pin to ground?.....I don't no if it matters but I'm also going to be using electric fans, will the ecm turn the fans on if the AC is on?
 

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