'98 Mustang Air Conditioner Not Working

yllw98stng · Jun 13, 2010

My air conditioner quit working the other day. I popped the hood and noticed that the compressor clutch was not engaging. What can I do to diagnose this problem. I jumpered the low pressure sensor switch and the compressor still did not engage.

wmburns · Jun 14, 2010

Start by checking the fuses. Next inject +12 volts directly to the clutch. This will verify that the AC clutch is working.

If the fuse is good and the clutch is good and the low pressure switch is working (or bypassed), it's time to start thinking about a bad CCRM.

yllw98stng · Jun 15, 2010

Ground as well

Ok, I pulled the electrical connection that goes to the clutch. I ran another wire from the positive terminal on the battery and poked it around inside the connector on the Clutch side, but nothing happened. I'm assuming I also need to make sure their is a ground to the clutch connector as well, correct? That's going to be rather difficult considering the placement of the plug.

yllw98stng · Jun 15, 2010

Oh yeah...

All the fuses looked good as far as I can tell. Also, I put my voltmeter probe into the plug that plugs into the clutch and I was getting 0 volts, so my guess is that there is no power even getting to the clutch. I will continue trying to apply power directly to the clutch and see if I can get it to engage.

wmburns · Jun 15, 2010

Did you test 0 volts on the car connector or the clutch side? If zero volts from the car side, then the power is not making it from the CCRM.

Note on fuses. You can't always tell from a top visual inspection.

Note, there is also a high pressure switch that if failed, could keep the AC from working.

There is also the function switch in the dash.

Review the following post. The wiring diagrams are going to be different for the 98 MY, but this should give you an idea where to look.

http://www.stangnet.com/mustang-forums/817829-c-not-working.html

yllw98stng · Jun 15, 2010

Progress

Ok, so here's where I'm at: I was able to locate the high pressure sensor and I jumpered/bypassed that as well as the low pressure sensor. The compressor still did not kick on. I went an bought some alligator clips and was finally able to connect the compressor clutch directly to the battery. Voila, the compressor engaged. So, at this point it does not appear to be the low pressure sensor, the high pressure sensor, the compressor, or the clutch. What does that leave me with to check?

I bought a cheap guage to measure the refrigerant pressure on the low side. It did not make a reading. This was while the compressor was not running so I guess that would probably make sense that there was no pressure. I manually made the clutch engage for about 60 seconds and then took another reading but it still did not register anything on the guage.

Is it possible that I'm completely out of refrigerant and that is preventing it from kicking on? I hooked up a can to the low side and kicked the compressor on again for about 60 seconds. I think it took some in, but again the guage read 0. I don't want to run the compressor for any longer than I have to, because I heard that could be bad on it.

Any suggestions?

yllw98stng · Jun 15, 2010

Sorry, we posted at the same time....

To answer your question, it was 0 volts on the car side of the connection.

In regards to the fuses, I pulled out the fuses under the dash and they looked good, but I did not pull out any under the hood.

I will see if there is anything I can mess with on the function switch and read your article as well and see where that gets me.

Thanks!

wmburns · Jun 15, 2010

Even if your Freon pressure were ZERO, jumpering the low pressure switch in a normally working system should MAKE the clutch engage.

Yes it is very bad to run the compressor that is low on Freon.

I suspect that your guage is not pushing the schrader valve. Therefore, the guage is not actually reading the pressure.

Zero volts from the car side says that the CCRM is not calling for clutch. Still have to find out what is wrong upstream.

Check the fuses under the hood. Would be a shame to do all this work only to find a blown fuse.

yllw98stng · Jun 15, 2010

The only fuse that seemed relevant under the hood was the one for the CCRM / PCM. It was good.

I made an offer for a CCRM on eBay, but would be extremely happy if I could get A/C before the weekend, without spending a ton of money on it.

yllw98stng · Jun 15, 2010

Here's the heating and cooling diagram from my Haynes manual.

Is the AC Clutch Cycling Pressure Switch the same thing as the low pressure switch? If so, then I believe I have ruled that out by jumpering it. I have also ruled out the High Pressure Sensor by jumpering it. This really leaves just the Heater Control Assembly and the CCRM.

It seems to me that if I could check the Dk Grn/Org wire going into the CCRM, that would tell me whether or not everything up to the point of the CCRM thinks the Compressor should engage. The problem is that I think you have to remove the fender to get to the CCRM, correct? I had it off last winter.....ugh....

But, I guess there is also the PCM which could also be the problem.

yllw98stng · Jun 15, 2010

I just had another thought. When I jumpered the high pressure sensor connection, there was +12V going through the jumper. Wouldn't that indicate that the Heater Control Assembly is working properly as it is allowing power to get to both sensors.

Ah! That gives me another thought...I think at one point in my troubleshooting yesterday I was not getting power to the sensors, but looking back, I'm not sure I had the switch in the A/C position.

Would that make sense?

Sorry for the "thinking out loud". I'm not neccessarily a mechanic by any means as you can probably tell, and this has definitely been a great learning experience. I greatly appreciate all your help so far WMBurns!

yllw98stng · Jun 15, 2010

I won the auction for the CCRM. I purchased a used one for $42 with shipping. It probably won't get her until next Tuesday unfortunately. Let me know if you have any other ideas in the mean time. Thanks!

wmburns · Jun 19, 2010

yllw98stng said:
I just had another thought. When I jumpered the high pressure sensor connection, there was +12V going through the jumper. Wouldn't that indicate that the Heater Control Assembly is working properly as it is allowing power to get to both sensors.

Ah! That gives me another thought...I think at one point in my troubleshooting yesterday I was not getting power to the sensors, but looking back, I'm not sure I had the switch in the A/C position.

Would that make sense?

Sorry for the "thinking out loud". I'm not neccessarily a mechanic by any means as you can probably tell, and this has definitely been a great learning experience. I greatly appreciate all your help so far WMBurns!

Look at your diagram. If you have +12 volts going to the low pressure switch, then the AC dash control MUST be in the AC position. The diagram says it has to be so.

To say there is only 1 relevant fuse is silly. The diagram points out two. I can't begin to tell you the number of times I have helped PPL that it turned out to be a blown fuse. Either they "looked" at it from above, or "checked it" at the start of work. Only to find out later that it was blown. So do yourself a favor and check all of the fuses. Pull them out one at a time and look at them from the side. Even better, test them with an Ohm meter. It may turn out that your CCRM is bad. However, wouldn't you feel dumb if it still did not work after the repair?

Yes the CCRM is a PIA to get to. Best to remove the right hand fender liner to access.

Have you verified there is Freon in the system?

FWIIW, per the diagram, the high pressure switch is a normally closed (NC) contact. The best way to test a NC switch is to disconnect and test with an OHM meter (or noid light or what ever you have to test basic circuit continunity). The only sensor that needs to be jumpered is the low pressure swich and only if the AC is low on Freon.

Finally, do you have an ODB2 scanner? If so, monitor the AC PID to ensure that the PCM is even calling for AC.

IMO, assuming that you have done all of the other tests correctly and the fuse is in fact good, the odds do favor a bad CCRM.

yllw98stng · Jun 28, 2010

It Works!

Sorry for taking so long to get back to you. The problem did indeed end up being a bad CCRM. I got it replaced and am once again enjoying Air Conditioning. Thanks for your help!

Kenforce · Jul 23, 2010

High pressure switch - Test

How exactly do you test the High pressure swith? Mine has four wires going to it and the diagram in this tread show 2 if I am reading it correctly.

I looked at my switch and I see these colored wires. Just worry about the Black and Tan/lt green?

Black, Tan/lt green, blue/yellow, and green/red

98 Mustang GT

Thanks,

Ken

wmburns · Jul 23, 2010

Kenforce, you are NOT reading the diagram correctly. The diagram shows (4) wires going to the high pressure switch. The high pressure switch has (2) contacts.

The first contact is a normally closed contact use to interrupt power for the AC control circuit. When high pressure is detected, the switch opens. The wire colors are DK-BLU/YL and DK-GRN/ORG.

The Second contact is a normally open contact that is used to tell the PCM when an over pressure condition is occurring.

To test a normally closed contact, use an Ohm meter to measure the resistance (open circuit). The value should be low indicating continuity.

Again, this is per the thread attached diagram.

Disclaimer. There are differences in the AC circuits depending on the model year and engine. Some MY’s have a one contact high pressure switch. Later MY cars, the PCM signal side is a normally closed contact.

Unfortunately, the diagrams included in Chilton’s and Haynes manuals are not definitive with regards to wiring diagrams.

Kenforce · Jul 23, 2010

wmburns

Thanks, I understand the diagram thanks to your explaination.

It's kind of funny now that I realize I was looking at only half
of the rectangle that represents the switch.

Thanks again!

rong1203 · Aug 21, 2010

wmburns said:
Start by checking the fuses. Next inject +12 volts directly to the clutch. This will verify that the AC clutch is working.

If the fuse is good and the clutch is good and the low pressure switch is working (or bypassed), it's time to start thinking about a bad CCRM.

What is the best way to supply the power to the clutch directly, I installed a brand new low pressure switch and even tried bypassing it, I was still not getting power to the yellow/black wire that came off the compressor.

Thanks in advance,

wmburns · Aug 21, 2010

Check fuses F1.24, F2.2, F2.23, F2.24. F1=BJB, F2=CJB.

Review diagram 54-2 and 54-3.

Did you test the high pressure switch?

Also, the mode swtich inside the can also cause the AC clutch to not engage.

'98 Mustang Air Conditioner Not Working

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