No Power to AC Compressor

[SpencerW]

High pressure cutout switch could also cause the issue. It breaks the same circuit that the low pressure switch closes when pressure gets too high. It is possible that it has failed. Installing a jumper in similar fashion to the low pressure switch would bypass it. Best thing to do would be to check for power at the hot terminal of the switches until you find your problem. Broken wire is also possible. You should have unswitched power at pin 30 of the relay, ground on pin 85, and your pressure switch circuit and control head will apply power to pin 86 when the AC is turned on. If all of those check out, it could be between pin 87 and the compressor clutch.

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I have a 97 LS swapped. Removed PCM and running TermX now. Trucks been done for 1.5 years, but never drive it because it's too hot for daughter. Trying to get the AC going. I'm having issues getting power to my compressor. I have no power going out the light green signal wire. Where does pin 30 go? Originally, I was running that to my compressor, but couldn't get power out of it either. I ended up purchasing an aftermarket setup and trying to integrate the factory AC button.
Thanks.

 

[SAATR]

I have a 97 LS swapped. Removed PCM and running TermX now. Trucks been done for 1.5 years, but never drive it because it's too hot for daughter. Trying to get the AC going. I'm having issues getting power to my compressor. I have no power going out the light green signal wire. Where does pin 30 go? Originally, I was running that to my compressor, but couldn't get power out of it either. I ended up purchasing an aftermarket setup and trying to integrate the factory AC button.
Thanks.

This may help:

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You are referring to the light green wire in the picture? From the AC control head to the high pressure cutout switch? Or one of the other green wires in the compressor control circuit?

 

[SpencerW]

This may help:

You must be registered for see images attach

You are referring to the light green wire in the picture? From the AC control head to the high pressure cutout switch? Or one of the other green wires in the compressor control circuit?

I think I have everything wired up. I ran the low pressure switch in line with my signal switch. I purchased a Holley AC kit. But the light green wire coming from my AC control head does not have any power.

 

[SAATR]

I think I have everything wired up. I ran the low pressure switch in line with my signal switch. I purchased a Holley AC kit. But the light green wire coming from my AC control head does not have any power.

I think that wire may be a switched ground. Have you checked continuity between the LG wire and ground with the AC on and off?

 

[Whaaaatnow]

Might could check live data with a scan tool to see if the pcm is getting the a/c request.

I’m having the same issue with my AC but I’m only getting 1.8 V at the low pressure switch and 1.8 V coming out of the computer is it that I have a bad computer?

 

[1998_K1500_Sub]

I’m having the same issue with my AC but I’m only getting 1.8 V at the low pressure switch and 1.8 V coming out of the computer is it that I have a bad computer?

Exactly what "issue" are you having?

You mentioned the low pressure switch, so going with that...

Measure the voltage across the low pressure switch.

It should be zero if (a) the AC is off and (b) the system has adequate charge and pressure to close the switch.

Alternatively, disconnect the electrical connector and measure the resistance across the switch. It should be low... zero to perhaps 1.5 ohms.

The AC won't run if these conditions aren't met.

There are other conditions which must be met too, but you've started with the "low pressure switch" so I'll stick to it.

I and others can tell you more if you provide more information, e.g., year of vehicle, operational status of the AC and other relevant factors.

 

[Whaaaatnow]

Exactly what "issue" are you having?

You mentioned the low pressure switch, so going with that...

Measure the voltage across the low pressure switch.

It should be zero if (a) the AC is off and (b) the system has adequate charge and pressure to close the switch.

Alternatively, disconnect the electrical connector and measure the resistance across the switch. It should be low... zero to perhaps 1.5 ohms.

The AC won't run if these conditions aren't met.

There are other conditions which must be met too, but you've started with the "low pressure switch" so I'll stick to it.

I and others can tell you more if you provide more information, e.g., year of vehicle, operational status of the AC and other relevant factors.

I have a 97 Yukon 4 x 4 5.7 AC used to work perfect had the engine changed AC never worked again. I had it recharged same difference so I tested to switch is ok if I jumper the relay, everything works fine some reason there’s no signal getting to the relay. seems like all my pressure switches have everything they need but when I disconnected my low pressure switch and check the voltage on the connector there only 1.8 V from my understanding it should be five or 12 V if I’m not mistaken.

 

[1998_K1500_Sub]

I have a 97 Yukon 4 x 4 5.7 AC used to work perfect had the engine changed AC never worked again. I had it recharged same difference so I tested to switch is ok if I jumper the relay, everything works fine some reason there’s no signal getting to the relay. seems like all my pressure switches have everything they need but when I disconnected my low pressure switch and check the voltage on the connector there only 1.8 V from my understanding it should be five or 12 V if I’m not mistaken.

OK, so check the switch as I suggested, let's see if it's sane.

Have you verified the system pressures with a gauge set?

Jumping the relay isn't a good idea except as a short test, you can force the compressor to run on a low charge and that's Not Good.

 

[Whaaaatnow]

I have a open Low pressure switch so I guess that must be my issue

 

[Whaaaatnow]

I have a open Low pressure switch so I guess that must be my issue

But if I jumper the connector, shouldn’t it kick on and yes, I did verify. I have enough pressure.