Engine Tips on how to troubleshoot and fix AC

AnthonyA1234 · Mar 12, 2022

Hello I just purchased a 1992 mustang gt. The compressor clutch does not engage. I’m not sure if the compressor is broken or if I just need to add more refrigerant. Can someone tell me the steps for how I can engage the clutch to see if it works. I understand there’s some sort of low pressure switch you can jump to engage the clutch to see if it works. Can anyone tell me where that is? Thanks.

General karthief · Mar 13, 2022

On the firewall behind the passenger side head, there is a small door, knock on that door three times, if no answer, its broken
But seriously, you will see back there a tank looking thing with a switch and two wire plug, jump the wires in that plug, pump runs, possible low freon, pump don't run, other problems,
Things to consider, just adding freon does not fix the problem, how long since it last worked? There is hi and low pressure involved, it can get pretty involved.

AnthonyA1234 · Mar 13, 2022

General karthief said:
On the firewall behind the passenger side head, there is a small door, knock on that door three times, if no answer, its broken
But seriously, you will see back there a tank looking thing with a switch and two wire plug, jump the wires in that plug, pump runs, possible low freon, pump don't run, other problems,
Things to consider, just adding freon does not fix the problem, how long since it last worked? There is hi and low pressure involved, it can get pretty involved.

I’m not sure, the car sat for 5 years before I bought it. I just got it running. Do I do this while the car is in auxiliary mode? Also to clarify, by jumping the wires you mean connecting the wires in the plug correct?

Bird76Mojo · Mar 13, 2022

What he's talking about is a pressure switch that won't allow the compressor to run if refrigerant pressures are low. So yes, you'll be using a jumper wire in the wiring plug itself. Don't let it run long if the compressor does kick on. Just long enough to see that the clutch on the compressor engages.

Mustang5L5 · Mar 13, 2022

Here’s a thread with some pics

https://www.stangnet.com/mustang-forums/threads/a-c-low-pressure-switch-plug-replacement.705606/

Jump this out. Start engine, turn on AC. Compressor should engage. Turn it off ASAP. You just want to run this long enough to see if it engages.

The switch is a low pressure cutoff. If refrigerant is too low, the system will not turn on the compressor. With it bypassed, the compressor should engage now.

AnthonyA1234 · Mar 13, 2022

Great I’ll try that today. Thanks for the info guys

AnthonyA1234 · Mar 13, 2022

So I did it and the clutch engaged and began spinning. I’ll take it to get recharged whenever I get the car on the road. Also, if any of you could help me out, the car has a gauge connected to what I believe to be the fuel Schrader valve so I assume it’s a fuel pressure gauge. It reads 30 at idle and correct me if I’m wrong but shouldn’t it be 40? The car has what I believe to be a fuel pressure regulator on the fire wall but I turned it and the fuel pressure didn’t change. Any info would be much appreciated.

Mustang5L5 · Mar 13, 2022

With the engine running, the pressure would be around 32-33psi. You need to pull the vacuum line off the fuel pressure regulator (located behind the intake “neck”) plug the vac line and read the pressure then. It should be 38-39psi. At idle, with vacuum connected the pressure will be slightly lower.

That knob you were turning is not for fuel pressure, it’s for the rear disk brakes. It’s an adjustable knee-point valve. It regulates the flow of brake fluid to the rear calipers so that you don’t get too much initial pressure at the rears. Hopefully you didn’t play with it too much.

General karthief · Mar 13, 2022

If you did the checklist it would help you but, anyway, that is a brake pressure adjuster on the firewall.

manicmechanic007 · Mar 13, 2022

See if the compressor turns by hand
Install gauge set see if pressure is above 28 lbs (should be about 80)
If low leak diagnosis
If gauge pressure is high / normal
Paper clip jump pressure cycling switch (most likely fault if freon is charged)

Engine Tips on how to troubleshoot and fix AC

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

Bird76Mojo

Mustang5L5

That is…until I whipped out my Bissell

AnthonyA1234

AnthonyA1234

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Mustang5L5

That is…until I whipped out my Bissell

General karthief

wonder how much it would cost to ship you a pair

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Engine Tips on how to troubleshoot and fix AC

wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

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That is…until I whipped out my Bissell

wonder how much it would cost to ship you a pair

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