MainePorsche

Has anyone had issue(s) with this, and what were it's symptoms ? I'm tracking a Gremlin.

Thanks in Advance.

MainePorsche

Sorry to bump this.

I know what this is supposed to suppress, but this 'relay' is tied into the the Fog Light Relay, Fuse 24 for the interior lights, and has output to the AC compressor clutch. 2 of these 3 are directly tied into to my Gremlin. I just would like to know what symptoms one would see if this unit were in some way faulty, and what is its normal function relative to the Fog Light relay.
Thanks
Craig

dr bob

It's a diode and capacitor surge suppressor that's there to quell surges from the compressor clutch coil when it disengages. Failure modes are open, which you couldn't detect, or shorted, which would pull the X bus low. If you are seeing 'problems' with foglight function as a symptom, and also erratic operation of some accessories that are powered off the X bus, the quickest/easiest/most common failure to solve is failure of the X-bus relay. It's a standard 53B relay, easy and cheap to source and replace. It's in position IV on your 1987 S4.

MainePorsche

Thanks dr bob.
My Gremlin is still the AC clutch wire goes to 0.0v when the light switch is turned to position 1 or 2.
AC work flawlessly with light switch off. I have an 134 system by Porsche via the PO.
I have been through everything. Algorithms by Alan, 14 pin connector, I've dissected and completely rebuilt the power harness, I've went through every ground and every wire in the center console, illumination/rheostat system. My CE board has been dissected, cleaned, and is nothing but factory. I've diligently removed the PO's keyless entry system as it had signal lights tied in. Freeze switch was no good. Bypassed and still no AC with switch on. Put in a new one - no change. System diligently fully charged. All systems in vehicle function as factory new.
I haven't addressed relay XI until now.
It's funny that if I hold the high beam lever back by hand I will have AC with forward illumination, but not via the light switch. I've put in a new light switch as the bulb kept on burning out. I thought I was maybe getting a ground loop feedback as this switch shares the ground with the HVAC controller. I'm almost ready to give up on the Gremlin.

dr bob

There's a known gremlin with the relay in the AC control head. Since you know where things are, do this simple test. Voltage betwee ground and freeze switch with lights off should be battery voltage or really close. Same reading with lights on?

-- If so and the AC clutch still drops out, you've isolated the problem to something forward of the freeze switch. In the factory circuit, the wiring goes through the pressure safety switch, the 14-pin and then the clutch connection at the harness by the dipstick. Some have added an external relay in that circuit, so the wiring from the freeze switch actuates the new relay's coil. Current from the jump post would pass through a fuse, then the relay contacts and on to the clutch coil. If someone has added that "helper" relay and it shares a soggy ground with headlights, you might get your symptoms.

-- If the voltage drops so much with lights that the clutch coil drops out, I'd start at that X-bus relay and move forward from there. If that doesn't take care of it, read up on replacement of that clutch relay in the control head. I'm not sure how it would be related to the lights on or off, other than the fact that they share power from the X bus. Do your headlights actually work when the light switch is on, and/or do you have the fog lights switched on when you have the problem?

MainePorsche

dr bob,
Thanks again for your attention. Had to go pick up my daughter from a Varsity County championship track meet.
With lights on I drop to 0.0v at the freeze switch. It seems as if the HVAC controller head relay has a ground feedback killing its output. I was also wondering if it were some defect on the board of the HVAC controller, for it does have a light activated through the black/blue illumination wiring. Odd though because all lights work just fine - no 'dimming'.
I am considering changing out the controller head relay to a more robust one via Dwayne's write up. I had also noted yours and Wally's suggestions about the 'external' relay scenario.
I'm just concerned for I have done quite a bit of diagnostic and therapeutic work, yet still have the demon. Also, no 'external' relay present pre-clutch wire

dr bob

f voltage goes to zero on the freeze switch terminals, I'd suspect the head relay first. My 'fix' for this has the relay external to the controller case, with exposed-for-testing wiring to the relay so it can be tested before it gets put back in the dash. We may be searching for "why the relay doesn't pull in" rather than "why the relay doesn't pass enough current to operate the clutch coil", so being able to get to those wires with a meter will be a big help. I'm not sure how Dwayne mounted his relay. I think the instructions I published a dozen years ago have been superseded by Dwayne's, where his uses a commonly available Radio-Shack part vs the industrial-strength relay I used on mine.

MainePorsche

What exactly do you mean by searching for 'why the relay doesn't pull in'...

I just find it very curious that the existing hvac relay works fine with the light switch off.
What is the cause for its functional fault ? - That is fundamentally what I'd like to fix, then I would feel comfortable in investing my time to add a relay so the existing hvac relay would only have to power the coil of an industrial strength relay that would power the clutch. Without addressing this fault I could still potentially not be able to power an added relay configuration or even if I just change out the relay to a more robust one it could still be without output.

dr bob

If the ground side of the head relay coil circuit is common with an external lighting circuit someplace, turning lights on would remove the potential across the relay coil. Relatively simple to find if the relay wiring is exposed. I'm fishing here, looking for a place to test the circuit back through the relay. The relay coil is actuated by the AC pushbutton on the panel insert. That might ber a place to look too.

MainePorsche

dr bob,
Pardon me for that question. I realize that it is exactly the issue I am trying to hunt down - where the ground feedback loop is causing the loss of potential across the relay coil.
I have considered the AC button on the central panel as one of the possible defendants. However it illuminates brightly when depressed with the light switch on or off. It illuminates less brightly when it is not depressed and the light switch is on. Normal.
I am leaning toward calling it a fault in the HVAC controller - board or the relay. I am 0.0v at the freeze switch with light switch on. Blower works fine - light switch on or off.
HVAC controller has always illuminated well (from a circuitry point of view - central face would light brightly - I did LED work there - no obvious 'trauma'/burns to Board or connections present - had this gremlin way before the LED work and still have it post work). Every other bulb/switch/etc. in the car works fine to the best of my knowledge. Not only do these work, but I have been through the wiring on all.

Alan

So - simply apply 12v from the jump post (via a 5 A fuse) to the freeze switch (either terminal - doesn't matter). Does the AC work fine in that config - Should.

Remove the freeze switch connections, with the car & AC on figure out which has ~12v with lights off - what happens with lights on?

This is important... The classic failure of the HVAC relay is terminal degradation - increases resistance - at no load you will see ~12v but with the clutch load you will see ~0v (can be tricky to debug). But external items like the lights should have no effect on this.

See if in your case even without load the voltage still drops - then if it does - indeed the issue is on the coil side of the HVAC relay. (and I would suspect a quite likely cause is that you installed an LED wrongly).

Alan

MainePorsche

Alan,
Greetings.
On this start, 13.9v running at Right point.
With AC on 13.6 at one freeze switch wire - 0.0 at the other one - This is with no lights
0.0v at both freeze switch wires with light switch on.
Interesting, fans activated with the wires disconnected from freeze switch when potentials measured.

I've had this problem long before the controller LED work

Edit: Correction: I'm not surprised the fans activated with the freeze switch disconnected from the line.

Alan

So either there is a fault with the HVAC head unit or its the changes you made. Honestly I'd expect its more likely to be related to the changes you made (but maybe something got damaged).

Try the DEF mode - this is another different way to turn on the AC Clutch relay- does this also drop out the clutch when the light are on?

Does anything else happen when you turn the lights on (distribution flaps change posistion?)

If you can measure the HVAC connector (while connected).

Pin 4 is ground and should stay at 0V wrt a vehicle ground point at all times (this goes to the ground side of the relay coil). Pin 11 is one source that feeds the +ve relay coil (via a diode), Pin 7 is the other source that feeds the +ve relay coil (via a diode). See what is happening on these under these conditions.

Otherwise take out the HVAC head unit dissassemble and test connectivity between Pin 3 (illumination) and the +ve side of the relay coil use diode tester in each direction.

Also do the same between the coil and Pins 7 & 11. Should conduct for these only in one direction when 7 or 11 are more positive.

Alan

MainePorsche

Alan,
Have to run now - family thing we're getting in the SUV for.
Will check pins on the hvac removal later.
doesn't work right in the Def mode as well.
Thanks.
Will get back to you.
Have a Great weekend.
Craig

MainePorsche

Alan,
I was in a rush and forgot to mention that distribution flaps DO change position when lights are turned on while AC button engaged. Fans remain on though.

Will run the algorithm and post.

Thanks,
Craig