Please Help Ac Compressor Will Not Engage

black97stang · Aug 27, 2015

Idk what's wrong with my ac the clutch wont engage their pressure in the lines I had to manually get it to turn on meaning I used some gasket maker the felt and cut out rings the size of the compressor clutch and stick in their to get to spin over to charge but after I charged it the clutch still won't engage and theirs probably a thread here on it somewhere I scrolled for an hour and a half and couldn't find one so sorry if this is a repost I just need some help please it's very hot in Florida I appreciate any help that's given

black97stang · Aug 27, 2015

I tried to jump the low pressure cutout switch and the clutch still didn't engage I'm getting 13v to the compressor through the bk/yw wire

wmburns · Aug 28, 2015

Should we assume that this is a 1997 GT?

IF there is power to the AC clutch BK/Y wire and the clutch does not engage, THEN:

The clutch field coil is open/shorted. Disconnect and perform an Ohm resistance check. If "open" then the diagnosis is confirmed.
The clutch field coil ground (the black wire) is not really providing a ground. Take a Ohm resistance check back to battery negative. Should be a very low value.

For further proof that the clutch field coil is bad you could try powering the clutch directly from a 12 volt source. With no electronics in the way either the clutch will "click" or not. Either way, you will know which direction to go next.

TuneUpsNSuch · Aug 28, 2015

Possible AC clutch relay fault in the CCRM. This is the relay module that contains the relays for fuel pump, cooling fans, ac clutch, etc. Usually mounted in the right hand fender. You'll have to remove the air cleaner assembly to access. I have replaced many of these for ac clutch inop.

black97stang · Aug 28, 2015

wmburns said:
Should we assume that this is a 1997 GT?

IF there is power to the AC clutch BK/Y wire and the clutch does not engage, THEN:

The clutch field coil is open/shorted. Disconnect and perform an Ohm resistance check. If "open" then the diagnosis is confirmed.

The clutch field coil ground (the black wire) is not really providing a ground. Take a Ohm resistance check back to battery negative. Should be a very low value.

For further proof that the clutch field coil is bad you could try powering the clutch directly from a 12 volt source. With no electronics in the way either the clutch will "click" or not. Either way, you will know which direction to go next.

How would I go about doing the ohm test I have a voltmeter handy just don't know what to do with the leads like + to bk/y wire and - to bk wire and how do I tell if it's an open circuit and no the 97 is my other car this one is a 2000 gt sorry I forgot to post that.

black97stang · Aug 28, 2015

wmburns said:
Should we assume that this is a 1997 GT?

IF there is power to the AC clutch BK/Y wire and the clutch does not engage, THEN:

The clutch field coil is open/shorted. Disconnect and perform an Ohm resistance check. If "open" then the diagnosis is confirmed.

The clutch field coil ground (the black wire) is not really providing a ground. Take a Ohm resistance check back to battery negative. Should be a very low value.

For further proof that the clutch field coil is bad you could try powering the clutch directly from a 12 volt source. With no electronics in the way either the clutch will "click" or not. Either way, you will know which direction to go next.

And also I tried to hook it directly up to a 12 source and it made a big spark on me so I think I did it wrong how would I try that I know the bk/y is pos and bk is neg

wmburns · Aug 28, 2015

The AC coil does draw a fair amount of power. So some sparking when first applied should be expected. If you are concerned then use a fused test jumper. Every time I have tried the test on a good coil the "click" of the clutch pulling in is immediate. And yes the black is ground and the BK/Y is positive.

But if the wire sparked, this means that some power is being drawn. So either the clutch air gap is sooooooooo large that the coil can't pull it in. Or the coil is shorted internally and the electricity isn't flowing all the way through the coil.

If the AC worked and now it doesn't and the air gap has grown excessively large, the the clutch has WORN out and needs to be replaced. Suggest taking the clutch pressure plate off and inspecting the friction surface. If deeply scored then it's time to replace it. The friction surface does ware.

Honestly. If this were my car I would much prefer to replace the clutch assembly instead of the field coil. Replacing a field coil with the compressor on the car is a total PIA!!!

How to take a continuity test.

use a fresh battery in the Volt-Ohm Meter (VOM)
disconnect the device to be tested from the circuit. It's not possible to get an accurate Ohm reading if there's voltage on the circuit under test.
Put the VOM meter into the lowest Ohm scale.
short the test leads together to "zero" the meter. This should read zero Ohms.
put the test leads on the part to test. Read the resistance. If the value is very low, there's continuity. If the value is very high, then the path is open.

black97stang · Aug 28, 2015

Ok I did the continuity test and it didn't even register I did zero it out first and put the leads on the little barbs where the plug goes and nothing it was at zero but while underneath I did notice the clutch does have a little bit of a gap to it but when it stops raining I'll try and jump the clutch again to see if it clicks and engages hopefully it's just the clutch I already found another compressor for $45 used they said it worked until he blew the motor up I looked just in case mine is majorly messed up so it could just be that the gap is too big for the coil to retract the clutch and that could be why it doesn't engage I'm not that great with electronics but I'm pretty good with working on cars xD what sucks is its almost just as expensive to buy the whole compressor as it is to just buy the clutch

black97stang · Aug 28, 2015

Or not just found out you can buy just the clutch part it's 30 bucks at autozone.com it's called an ac clutch hub

wmburns · Aug 29, 2015

black97stang said:
Or not just found out you can buy just the clutch part it's 30 bucks at autozone.com it's called an ac clutch hub

IF going this route AND the field coil is good I recommend buying a Motorcraft brand AC clutch. You will thank me later when you don't have to remove the field coil. Why use a motor craft brand? Because an after market clutch is designed to work with the after market field coil. The need to be kept as an assembly. So while you save a few $$'s on the clutch, the effort required to swap the field coil out weighs the $$ saved by a long short.

Of course since you have a Used Ford compressor would would assume that you have the Motor Craft parts in your possession.

IF the field coil is bad, then it doesn't matter which clutch assembly that you buy.

NOTE; it doesn't make sense the Ohm test is open but the field coil sparks when powered externally. Recommend that you double check your work as a mistake here could cost you $$'s in parts and wasted effort.

iowadude41 · Jul 16, 2019

wmburns said:
Should we assume that this is a 1997 GT?

IF there is power to the AC clutch BK/Y wire and the clutch does not engage, THEN:

The clutch field coil is open/shorted. Disconnect and perform an Ohm resistance check. If "open" then the diagnosis is confirmed.

The clutch field coil ground (the black wire) is not really providing a ground. Take a Ohm resistance check back to battery negative. Should be a very low value.

For further proof that the clutch field coil is bad you could try powering the clutch directly from a 12 volt source. With no electronics in the way either the clutch will "click" or not. Either way, you will know which direction to go next.

Sorry, and I apologize for this very late reply. I have a 96 mustang gt 4.6L, and my a/c compressor will not engage. I did jumper the low side pressure switch, and the clutch did engage. So I bought a new switch, but still have same problem. I did resistance check on the clutch, and it was good. Also have 12v at the clutch from the battery. My stupid question is this: How do I check the voltage at the plug when both wires are black, and no yellow stripe?

I also found that I have a freon leak at the low side service port. I noticed that the shrader valve inside has broken, and I can not remove it with the tool. I want to remove, and replace the entire service port, which can be done, but nobody seems to want to give me a direct answer to this problem. This might be my whole problem to the a/c not working. Can you please help????

wmburns · Jul 16, 2019

iowadude41 said:
I did jumper the low side pressure switch, and the clutch did engage. So I bought a new switch, but still have same problem.

Whoa nelly! Are we guilty of over thinking this a little?

IF the clutch engages when the low pressure switch is jumped THEN the system is working as designed. Have you considered for a moment that the reason why the AC clutch won't engage is because it's low on Freon?

When the AC clutch engages do the pressure gauges change?

If you are hell bent on looking for something to be wrong, then look at the possibility that the low pressure switch isn't actually opening the service port the low pressure switch isn't actually "seeing" the Freon flow.

iowadude41 · Jul 17, 2019

I really appreciate your blunt answers, I really do. I know a lot about cars, but this is something totally alien to me. I did come across the shrader valve inside the low side service port, and it actually looks like the top of it has broken off, and I can't remove it. The service port is leaking freon, but I did add some to put it back into the normal range, and turned on the a/c for several minutes, but it only blew hot air, and the clutch did not engage. I'd really like to replace that service port, and put in a new shrader valve to stop the leak. They actually sell the service port, but can it be removed or do i need to replace the entire service line? I can live without my a/c, but it is so hot and humid here in Iowa right now. Any advice on this would be very much appreciated.

wmburns · Jul 18, 2019

It's been awhile since I sold my 1996. But I seem to recall that the low pressure switch is located on the receiver dryer. If so if the Schrader value is broken and it can't be removed it seems the next option is to replace the receiver dryer.

I can certainly see a case that if the tip of the Schrader valve is broken, then the valve won't really be open when something like the low pressure switch is screwed in.

If the port is leaking on a hard line and the in service replacement add on won't work, then I don't see any other option but to replace the hard line. I have had some luck using Rockauto for parts such as this. However these are Chinese made parts which depending upon the part can go from great to just plain terrible.

tsemmett · Jul 18, 2019

On my 98, the service ports (high and low) are threaded onto the hard lines, and were pretty easy to replace with a wrench (they're just barely indexed for one). Some of the parts chains carry them (O'Reillys is where I got mine), and should already have o-rings/thread sealant on them.

I never did see a way to replace just the valve when I was doing this, but the ports weren't expensive enough for me to waste a ton of time either.

iowadude41 · Jul 18, 2019

tsemmett said:
On my 98, the service ports (high and low) are threaded onto the hard lines, and were pretty easy to replace with a wrench (they're just barely indexed for one). Some of the parts chains carry them (O'Reillys is where I got mine), and should already have o-rings/thread sealant on them.

I never did see a way to replace just the valve when I was doing this, but the ports weren't expensive enough for me to waste a ton of time either.

Thank you. Finally someone who could answer my question. I'll have to use a pair of vice grips as all of my sockets, and wrenches won't do the trick. I'll buy a new service port and get the job done this weekend. I very much appreciate your reply. Thank you again so much....

Please Help Ac Compressor Will Not Engage

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