Need some help diagnosing an A/C issue!

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DieselDan

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Hey guys, I've got an A/C issue and maybe need a little help diagnosing the problem...

Here is my problem, last week the A/C quit. I assumed it was just low on refrigerant and gave it a quick check. The pressures are good so, that isn't my problem.

Here is a copy of the diagram -
a798aff03a57658737cea673532bbcba_zpsf6ede971.jpg


Checking the power at C118 pink wire. This is the connector that connects the engine harness to the body harness. Below is a video showing what kind of read I am getting from it.
http://youtu.be/tFkaoZU8qYg

The voltage is very irratic. Sometimes the test light is extremely dim, and other times the light gets very bright like in the video, and the clutch intermittently engages. I need to check my voltage at connector C121, but I am leaning towards this kind of voltage reading being a bad VCRM? Looks like the VCRM is a pita to pull out to back probe, but I'll check it out this afternoon. My question is if anyone has had a similar experience with this.

The problem is also dependent on the car's temperature. Usually when I first start the car, the clutch won't even try to engage. As the car warms up, the clutch is more and more likely to engage. There is no change if I jump the Low Side cycle switch, so this is not a refrigerant issue. Any help is appreciated, I haven't really screwed with the VCRM before.
 
I would be guessing like you are, but the VCRM sounds like the issue, I think your on the right track.
I have no experience with it, just what I have read.

If you lived up here, I would tell you to roll down the window :p -11 degs today. :give
 
With that type of fluctuation as indicated by the test light, I would not automatically look at the VCRM. Might be as simple as a bad ground, a weak relay, or a bad pressure switch. And as you indicated that as the car warms up the clutch will engage and run the compressor, I would be looking at the A/C Refrigerant Pressure Sensor.

I just had my system checked and the A/C guy told me that it was not a Refrigerant issue as the pressures were within specs. Wanted to charge me like $300 to vacuum out the system and do testing. I stopped at AZ and got a recharge kit and after a whole can of AC Pro it finally works. Had the guy recheck the system and he stated that the pressures had not changed a bit, but he could not explain how my system was now miraculously working. And it has continued working for the past few weeks.
 
Well, I have bypassed the cycle switches, so it is not a refrigerant problem.
 
Sometimes a test light might not give you the most best reading. I would get a dvom and check the actual voltages. I would also see if you can get an ohm factory spec on that cycling clutch and ohm check with the dvom. It may have a high resistance which may be a shorted cycling clutch. It would explain the fluctuating bulb light. I would also take the belt off and see if the pulley on the clutch is binding. Some thing to do before you look at the vcrm. Hope that helps
 
Dan, you bypassed the pressure switch? As for the VCRM, it's easy to get off. The one on my car now came off the 93 that my dad wrecked. I took it off and sent it to Jamie and he put it on the 95 I bought. Not too bad to deal with, if that's the problem and it very well can be.
 
Unplug the compressor and see if it still does it with no current draw, I would say bad ground motor/body but I would think you would see it show up in other electrical gremlins.
Bad relay in the vmrc would be my next guess.
If you supply power and ground to the compressor does it work as it should?
 
If I supply power to the compressor, everything works well and the temperature out of the vents will get down to 38*. I had thought about checking that voltage with the compressor unplugged to see what it was with no draw. I have had super limited time to look into this, just because we are closing on a house today and my wife is 35weeks pregnant. She is a boss, packing and such, but with my 2yo son running around, my only real diagnosis has been before work at 3am. Just trying to brainstorm before I get my next chance to do more diagnosis. Thanks for the help guys :)
 
DieselDan said:
If I supply power to the compressor, everything works well and the temperature out of the vents will get down to 38*. I had thought about checking that voltage with the compressor unplugged to see what it was with no draw.
Click to expand...
That is good news
DieselDan said:
I have had super limited time to look into this, just because we are closing on a house today and my wife is 35weeks pregnant. She is a boss, packing and such, but with my 2yo son running around, my only real diagnosis has been before work at 3am. Just trying to brainstorm before I get my next chance to do more diagnosis. Thanks for the help guys :)
Click to expand...
More good news, congrats x2
Hope the house has a good man cave, pics when things slow down a little!
:cool:
 
You have been busy lately. Didn't know you had another lil one coming. :) I can imagine trying to move with a woman's help and only having time before work to diagnose a problem like that. I think you'll be alright without air at 3am and waiting until you finally get moved into the new house. I know you got one with a garage this time??
 
Hey guys,
I need someone to help me out... I need the voltage reading from the DLC plug, attached to the LF strut tower under the hood. I need to know the voltage on pin 6, it is a pink wire with a light blue stripe. Mine is about 6v, but I actually think this May be right. My car is a 94, not sure if it is year specific. In my diagnosis, that is the only wire (that circuit goes directly to the VCRM) that doesn't either have 12v or ground.

I thought I only had an AC issue, but while working on the car, it overheated. The engine fan isn't working and that also is controlled by the VCRM. I'm headed to the JY this morning to grab a VCRM, because that is the last thing I can come up with. The fan and A/C clutch will engage if jumped at the VCRM plug.

Thanks guys!
 
If the fan won't engage for some reason the computer will prevent A/C compressor/clutch from engaging. I had the same problem and thought there was something wrong with the A/C until I realized the fan wasn't coming on. When that came on the A/C came on.
 
Well, after doing all of the diagnosing that I thought I could, I decided the VCRM was bad. I went to the upullandpay and picked one up for $7.02 out the door. They charged me for a large relay, which I guess it really is. Slapped it in and all is working again, grateful to have A/C again!
 
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