Michael Benno

I am trouble shooting why my AC system on my 1988 S4 5spd is not working after a recent TB/WP job done by the dealer and I came across these wires that were cut by one of the many PO. The wires are coming from the wiring harness that goes to the Temp II sensor on the right side of the motor. The wires are color coded Red/yellow and Brown/Yellow.

In my sleuthing, I noticed a missing connector on what looks like a check valve connected to the fuel system or possible a vacuum line to the fuel diaphragm on the front of the car.





I should note the car runs and drives fine. No issues, other than the previous issue with AC system.

Can some someone help me identify the source/purpose of both of these? Are there any good reasons why these would be cut/disconnected?

Context pic

Rob Edwards

Yes, that cutoff pair of wires should go to the 2-pin AMP connector which is the fuel tank vent solenoid valve. I think you want that to be connected, I had a failure of that solenoid valve, which led to my gas tank collapsing. Made for some nerve-wracking reinflation fun:

https://rennlist.com/forums/928-foru...el-sender.html

Roger's got the 2-pin AMP connectors for cheap.


Theory of operation on the vent valve

mark928gt

My wire covering these two wires is frayed so I was able to confirm these are the same wire colors you noted. They do go to the electrical connection that you show. It looks like it is connected to a diaphragm valve for some sort of breather system. Others will be able to tell us exactly how the system works.

StratfordShark

Michael as part of the TB job the connection to the AC electric clutch has to be disconnected, so that the wiring loom can be unthreaded and allow the covers at front of engine to come off. It's a thin single wire - brown or reddish brown I think - that connects via a spade connector to the female coming from the clutch. Have you checked that one is plugged back in? It will be somewhere in front of the right hand side cam cover. I think that's the only electrical connection to the AC that is disturbed during the TB job

Michael Benno

Oh thank you very much for the tip! I'll check it out right away! I was gonna post a separate thread about the AC once I did a little more research. But I do think your suggestion is good. When I turn on my AC the clutch is not starting. It was working fine previous to the TB.

Michael Benno

Thanks for the detailed explanation. I'll get it fixed. If you have any info on how to test the controller or the valve let me know.

WallyP

The AC clutch is powered by a single black wire, with a single-terminal connector located very near the oil dipstick.

Jsulli

What is the top side of that wire supposed to connect to? My Ac clutch quit turning on and I found that wire had broken from whatever it was plugged into. I can apply 12v and the clutch kicks on, just not exactly sure where it broke off from. I think its the solenoid on the cross bar?

Sorry not trying to hijack.

Michael Benno

hijack appreciated, as I am trying to get some information about the wiring connections to the AC compressor clutch as well. I'd like to know if this can be checked from the top or do I need to drop the lower engine cover panel. I looked at from the top this morning and could see no wires or connectors to AC compressor clutch. So any pics of the connector wire would be appreciated.

I found this pic online, I see the spade connector, but wondering where the connection may be. I didn't see it in my recon this AM.

StratfordShark

It can be checked without removing undertray. Identify the thick engine loom strung across front of engine, mounted to bottom of centre lifting shackle by two clips. As you look at the front of engine there should be a single wire emerging from the loom on the left side. The end of the wire has a small rectangular plastic piece covering the connector, and the power feed to the compressor would normally be plugged into that.

PorKen

Not mentioned in the factory doc is that the LH also increases the injector time a tiny bit to match the air leak from the vent.


(Why do I know this? I modified the vent code so I could control a set of exhaust cutouts with a different solenoid valve. )

Rob Edwards

All sorts of Easter eggs (albeit physiologic) in that 32K of space, no?

G.P.

I used a JDS Spanner to check my fuel tank vent solenoid valve, along with all the other sensor checks. I found that it was not working.
When I pulled it apart it was clogged with charcoal from the charcoal canister. I found this was due to the vacuum diaphragm between the charcoal canister and the fuel tank vent solenoid valve being defective.
I was able to clean out the fuel tank vent solenoid valve and get it working again, and replaced the vacuum diaphragm.
The fuel tank vent solenoid valve operates when you put 12V across the terminals (I did this when it was disconnected and on the bench). You will hear it click when you connect the power and you will notice that you will not be able to blow air through it when power is connected (or maybe it was the other way around, you can blow air through with power connected). Anyway, if you find it's not working check for a blockage.

Rob Edwards

Here's the connector that the AC compressor clutch power wire plugs into. There's a .250" male spade connector deep inside- kind of a PITA to get connected.

Michael Benno

Thanks for the tip. I was able to find my connection and verify it was connected. Looks like my next step is to take it in and check the charge.