2000 Mustang Gt - Ac Compressor Clutch Not Kicking On Unless I Jump It.

jayrw · Jun 26, 2013

2000 Mustang GT w/ 95K miles, My AC stopped working recently, the AC clutch doesnt turn on and the engine RPM is erratic at idle with the AC dial in any position other than Off or Vent.

Friend of mine told me to jump the low pressure switch with a paper clip and sure enough this makes the AC Clutch kick on and the air works properly along with smooth engine idle, Also tested the pressure with a gauge and freon level is full.

Is it safe to assume under these conditions the low pressure switch itself is bad?

If so is it possible to change this switch by myself without having to empty the R134 from the system? I wasnt sure if removing the switch would cause it to empty the freon etc.

Thanks!

Mustang5L5 · Jun 26, 2013

I'd suspect the engine idle and a/c are unrelated. With the A/C compressor off, nothing should affect idle quality.

It's possible the low pressure switch is bad if you put gauges on the car and confirmed that the a/c system is fully charged.

I'd recommend taking the car to an a/c shop if you are not familiar with a/c repair. If the switch is bad, you will need to drain the system to replace it. In order to avoid introducing moisture to the system, you want a shop to do this, and pull a vacuum and refill.

jayrw · Jun 26, 2013

Ok Thanks, I guess its not going to be a cheap repair then.

The engine idle is only erratic when I try to run the AC without jumping the AC clutch. When the AC is turned Off the idle is fine.

Mustang5L5 · Jun 26, 2013

That's strange. Are you sure the compressor is not kicking on? I wonder if there is an electrical issue?

So unplugging the low pressure switch and jumping it out...ac work fine and can turn it on and off from inside the car?

But plug the low pressure switch in and the idle goes to hell but compressor is not engaged?

Sent from my iPhone 4S using Tapatalk

wmburns · Jun 27, 2013

jayrw said:
If so is it possible to change this switch by myself without having to empty the R134 from the system? I wasnt sure if removing the switch would cause it to empty the freon etc.

Thanks!

The AC low pressure switch can be changed without draining the system. There is a schrader valve that will keep the Freon from escaping. Easy job.

As for being able to tell if the switch is bad. Unless you post the pressure readings, not really possible to determine if the switch is bad.

Or you could replace the switch and see.

jayrw · Jun 27, 2013

wmburns said:
The AC low pressure switch can be changed without draining the system. There is a schrader valve that will keep the Freon from escaping. Easy job.

As for being able to tell if the switch is bad. Unless you post the pressure readings, not really possible to determine if the switch is bad.

Or you could replace the switch and see.

I tested the pressure with an R134a refill bottle that has the pressure gauge already on the hose, it was reading around 45 psi which was inside the Blue portion of the gauge reading (I didn't add any R134a from the bottle) I think that indicates it has plenty of pressure at least for proper operation of the switch?

I can re-test and get an exact number if that would help.

The AC was blowing cold when I had it jumped with a paperclip.

Thanks.

jayrw · Jun 27, 2013

I went ahead and changed the low pressure switch and that fixed it! Took about 2 minutes to change.

o'reilly's auto parts had it in town for $13 (They list the part as an A/C Clutch Cycle Switch)

Its going to be 109-112F here for at least the next 7 days so I fixed it just in time lol.

Thanks for the help!

jayrw · Jun 27, 2013

Mustang5L5 said:
That's strange. Are you sure the compressor is not kicking on? I wonder if there is an electrical issue?

So unplugging the low pressure switch and jumping it out...ac work fine and can turn it on and off from inside the car?

But plug the low pressure switch in and the idle goes to hell but compressor is not engaged?

Sent from my iPhone 4S using Tapatalk

Yep exactly those symptoms, I think the idle was erratic because it was trying to kick on the compressor every 2-3 seconds and it would cause the idle to briefly drop each time as well.

Changing the switch did the trick tho everything is back to normal.

Mustang5L5 · Jun 27, 2013

Glad to hear.

Also glad to see it can be changed without draining the system

antknee · Jul 5, 2013

interesting- i have the opposite issue..my a/c clutch wont turn off when the car is stopped, ignition off. so it drains the battery and i need to get it jumped- i dont suppose there is an easy fix for this too? as it is, i have to remove the fuse(?) from the CCRM when i park the car or the battery drains.

any input?

Mustang5L5 · Jul 6, 2013

Unplug the compressor. Does it turn off?

wmburns · Jul 6, 2013

This is either a bad CCRM or a wiring fault.

Are you interested in trouble shooting the CCRM? Do you have a VOM and are you willing to use it?

If no, then consider just replacing the CCRM.

apothicca · Jul 25, 2017

Mustang5L5 said:
I'd suspect the engine idle and a/c are unrelated. With the A/C compressor off, nothing should affect idle quality.

It's possible the low pressure switch is bad if you put gauges on the car and confirmed that the a/c system is fully charged.

I'd recommend taking the car to an a/c shop if you are not familiar with a/c repair. If the switch is bad, you will need to drain the system to replace it. In order to avoid introducing moisture to the system, you want a shop to do this, and pull a vacuum and refill.

Old thread but question, if I can jump the low-pressure switch and the compressor comes on it is either freon or the switch is bad correct? What is the right psi for the freon? Thanks!

2000 Mustang Gt - Ac Compressor Clutch Not Kicking On Unless I Jump It.

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