[Cloud9...68]

Yeah, its connector ends were easy to find. I'm planning to take the car to the shop (feels so strange to hear this terminal DIY'er say that...) to have its A/C checked, so I'm glad I was able to re-connect this key component of the A/C system.

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[rl968]

My tube is in tact and my dash control unit works (i can hear click for the heat and click back when i turn it down o cold) and is connected properly as I pulled it (very easy to do). I'm going to have to go back and have the compressor rechecked. It's a reman denso that was just put in so I assume its good, but maybe not. Not much else I can check and I don't have hvac skills or tools. Are there places that will check AC operation for free?

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[rl968]

I revisited this today, and it seems my compressor is NOT turning on when the button is pushed on the dash. I thought it was as could see rpms moving a little, but a friend watched when i hit the button and nothing happened, The fans kick on, which i probably what i was feeling, but compressor not engaging. Anyone know how the wires run? I have a wiring diagram, but not real confident in reading it, though I will try. Also, does the compressor hot share power with anything else?



Thanks

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[Paul W]

How do you know the system is charged? I am not familiar with the 968 system, but I can say with 99.9% certainty that there is a low pressure cut out switch on the compressor system. It would be a mechanical switch that allows the compressor to be energized, i.e. the 12 VDC goes to the compressor clutch. Most systems also have a high pressure cut out switch also. If you lost your charge, the low pressure cut out switch would not be permissive (closed) to energize the compressor clutch.



I would have to look at the wiring diagram, but there are only a few things that will prevent a compressor clutch from energizing, and most likely a low pressure cut out switch could be the cause. The switch could have failed, or something could have knocked the wiring off it.



Did you do any maintenance prior to the AC no longer working? If so, what was it?

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[rl968]

Thanks. I had the compressor replaced because an ear had broken off and the tensioner broke. When they put in new compressor, it was all charged up, but no power to the compressor apparently. It was working the last time I ran it, which was probably a year or so ago. I didn't want to pay more hours of labor since I dont use the AC really and figured I'd try to troubleshoot myself. My mechanic assures me system is full.



Where is the pressure switch(es) located?

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[Paul W]

I am busy right now, but I will look at the wiring diagrams later....I bet it will be easy to figure it out. They put the compressor in, it didn't work, and then everyone agreed to leave it be? That's too bad. We'll get to the bottom of this.

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[DaveN]

There is only one wire to the A/C clutch, very simple to troubleshoot - 12 VDC yes or no. I replaced my 944 S2 clutch a few years back as the coil burned out.

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[rl968]

If the answer is yes, then it would be the clutch. If the answer is no, then it's more complicated and I have trace back why there is no power. Is the correct?

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[DaveN]

Yea, if you get 12 VDC at the black wire and the clutch doesn't engage the compressor then I would remove the clutch and inspect. You can use an Ohm meter to check the winding. My S2 one was physically melted but you might just have a mechanical issue with the clutch plate not grabbing/actuating due to dust/rust/oil etc.

I just sold a new clutch to one of the members here for 300.00 but it cost me over 500.00. Partly because I live in UPS shipping hell, Canada, but also becasue it had to come from Japan to Germany to US (Sunset) to Canada. It's actually a Nippon Denso part.

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[rl968]

There is no power at the compressor. Pressure switch is next I think. Does system have to be purged when switch s replaced, if it is the cause?

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[Ryan]

I had a head unit go bad on my 944S years ago. I did all the tests and the clutch checked out fine. I replaced what looked like a good working head unit and that did it. As I recall that thing was $350.00 so I hope you find a wire off some where and it is simple.



As I recall the low pressure sensor is on the high side input down low near the compressor. Check to make sure that wire is on the unit. I did not know there was a high pressure sensor.

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[DaveN]

I have not looked at the wiring diagram but if there is no power on that wire then one would assume there is a relay at the other end to check next?

FWIW my lead was a bit crispy so maybe you have a short to ground somewhere along the line.

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[rl968]

Yes, that is the problem, tracing the wire, it's not so easy.

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[Paul W]

I went out and looked at it. The high pressure and low pressure switch are both installed in one component near the driver's side (LHD) AC line. You can see them here:





[sharedmedia=gallery:images:2410]



[sharedmedia=gallery:images:2411]



There are four wires that go to the switch, all 1 mm. They are:



Low Pressure: Black/Red, Black



High Pressure: Red/White, Brown



See the wiring diagram, the black from the low pressure feeds the AC compressor clutch, which is then grounded through the chassis of the compressor.







[sharedmedia=gallery:images:2409]



This is what I would do:



Determine how many fuses there are for the AC system, and check all of them that they are good. There is most likely more than one power supply for it, but I am unsure. See if this fixes the problem.



Disconnect the connector, using a multi-meter, with the car running and the AC on, check the voltage at Pin 4 (Black/Red) to ground. If working normally, you should have 12 VDC, if no voltage present, you have an issue upstream, which it gets its power from the AC relay. That would need to be troubleshot. Now that I am looking at the wiring diagram, the AC relay is the device that energizes/deenergizes the AC clutch. If no 12 VDC while the car is running at the low pressure switch, then you have to go in the upstream direction to the relay.



If you have 12 VDC on Pin 4, then turn the car off, and measure the resistance of Pin 1 (Black wire) to ground. You are reading the compressor clutch resistance. I imagine it would be in the range of 5-12 ohms. If it is an open circuit, then there is an issue in the wiring to the clutch or the clutch itself is bad (coil gone bad).



If you have 12 VDC on Pin 4 and continuity through Pin 1 to ground, then you need to check the low pressure switch. You can check the continuity of the SWITCH terminals 1 to 4, and you should have a circuit that is less than 1 ohm. If open circuit, the switch is bad or the system does not have an adequate R-134A charge.



If you have continuity from Pin 1 to ground, you could just jump 12 VDC from the battery to Pin 1 on the connector, and see if the compressor clutch picks up. You will hear it.



Do these tests and report back.



I have to say that this was the most challenging post I have ever made in my life. Took me forever to figure out how to get an album, then I made a monster reply, then hit preview, then hit the picture, then hit back and lost the ENTIRE post. It would be so much easier if I could just host the pictures, I can FTP them up and know the code. I like the forum software, but it is sure not like anything I have ever used before. I like to post pictures, and it's just very complicated to have someone else host them.



Is there a way to get the pictures to show in the post instead of the link I attached? I want them to appear in the body of the post, not as an attachment at the end.....I'm sure there is. Somebody help this poor guy out! ;-)



<rant off>

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[rl968]

Paul, this is really helpful. I need a little time to run through all this and may not get to it until the weekend, but thanks very much. I'll report back I did check the fuses, and there is only one that I can see, a 7.5 amp located in slot 29 in the fuse box. Is this the only fuse box in the car? That fuse is fine, I tested it for continuity. I didn't see a white/red wire, but it must just be dirty and I'll clean it off.



One thing that puzzled me a little on the wiring diagram was the red/white running to what appears to be the radiator (G10 relay). Not sure why it would do that.



Edit,



Going a bit out of order, but with my multimeter set to measure ohms, I put one lead on the black lead of the plug and the other to ground and got nothing. This leads me to believe there is an issue with the connection from the compressor to the plug...yes? I need to check the other connections, but this could be the issue, or at least one issue.

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[Paul W]

[quote name='rl968' timestamp='1376352735' post='147111']

Paul, this is really helpful. I need a little time to run through all this and may not get to it until the weekend, but thanks very much. I'll report back I did check the fuses, and there is only one that I can see, a 7.5 amp located in slot 29 in the fuse box. Is this the only fuse box in the car? That fuse is fine, I tested it for continuity. I didn't see a white/red wire, but it must just be dirty and I'll clean it off.



One thing that puzzled me a little on the wiring diagram was the red/white running to what appears to be the radiator (G10 relay). Not sure why it would do that.



Edit,



Going a bit out of order, but with my multimeter set to measure ohms, I put one lead on the black lead of the plug and the other to ground and got nothing. This leads me to believe there is an issue with the connection from the compressor to the plug...yes? I need to check the other connections, but this could be the issue, or at least one issue.

[/quote]



If you measured pin 1 (black wire) to ground and got an open circuit, that would mean:

• There is an open circuit in the wire from the connector to the wire that connects to the compressor. You'd have to find that wire/connection and perform a continuity check between the two to rule those out.
  
  
• There is an open circuit in the compressor clutch circuit. Once again, if you were down at where the black wire connects to the clutch, put the multimeter directly on the clutch to ground and see if you still have an open circuit.
  
  
• If you have an open circuit at the compressor, either the ground is bad or the compressor clutch winding is open circuited and you need a new one.
  
  

The other thing I would do is to turn the car on, and measure the voltage of Pin 4 to ground with the car running, the AC on, fan on, and the temperature set to low. If you get 12 VDC there, then you know it's something on the switch/compressor clutch side.



Sounds like you are quickly moving along....you just need to half split it, the switch is a great place to do that.



Good luck!

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[tamathumper]

To answer your question from a bunch of posts back, at least on the PT Cruiser I just repaired, the low side cutoff switch is installed over the top of a Schrader valve, so the switch can be screwed off and replaced without losing any refrigerant. I can't say that's the case for the 968, but it's worth looking into.



Believe it or not, the test to see if the switch is bad is to remove the electrical connector from it and short it with a paper clip. If the fans come on, then the system has lost its charge, or the switch itself is bad and needs to be replaced. The one I just bought for the PT Cruiser was less than $20.

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[rl968]

I think if switch is removed, system needs to be recharged and i want to avoid that.

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[Paul W]

There is really no reason to remove the switch, but there is a very good chance that it has a shrader valve on it. Here is a basic procedure with pictures I wrote many years ago on how to do a "poor man's recharge" on an Audi A8, you can see the low pressure switch removed, it has a Shrader valve on it where you can then connect a fitting to charge it.



http://forums.quattroworld.com/a8/msgs/15213.phtml

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[tamathumper]

Just to clarify, the switch only has to be removed if it is bad and needs to be replaced. You can remove (and test) the electrical connector without removing the switch.

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