MainePorsche

Good Morning Alan.
I agree.
I had already checked and recorded the voltages at the pin connector in my 'Suppressor Relay Question' post. In the next 15 mins or so I am going to do your above mentioned bulb test and compare the brightness. Does one do a continuity check or resistance check against a known good ground point ?

Edit: Got it. Will check resistance between pin 4 ground and a known ground. Almost finished with my coffee.

MainePorsche

The measurements were taken with light switch Off, light switch ON fogs OFF, and light switch ON fogs ON
Results:
Light switch OFF - Pins 1 - 9 0.0v, Pin 10 13.7v, Pin 11 & 12 0.0v, Pin 14 0.0v, Pins 13 & 15 0.1v
Light switch ON fogs OFF - Pins 1,2,4,6,8,9,11,12,14 0.0v Pin 10 13.5v, Pin 3 12.4v, Pins 5 & 7 0.4v, Pins 13 & 15 0.1v
Light switch ON fogs ON - the same os 'fogs OFF' with the non significant difference at Pin 11 at 0.2v

These were the voltages at the connector.

Lorenfb

"I doubt it is a diode (any of them really)."

That is correct, i.e. the diodes rarely if ever fail.

"Even if they fail (and they almost always fail open circuit) the majority of them will have no functional effect at all - certainly not this."

Actually this is not correct, as they usually fail in the shorted condition.

MainePorsche

With the DMM set at 200 for resistance measure, I had 0.6 at known good ground point.
I had 2.7 at pin 4 on the external connector.
Hmm...

MainePorsche

Though this wasn't a definitive maneuver, I disassembled pin 4 from its housing and checked its splice. All looked good. I then ran a new wire to ground point. Still at 2.7ohm and with anomalous function. One more move to make, and that is to change its ground point. I still find it hard to believe the ground point is resistant. It still has a reflective shine on it from my servicing it last year. All electrical functions that would attach there are fine. I am quite meticulous when I say all functions are fine.
One last maneuver and that is to change the ground point. If that doesn't to it I am considering making a switch to activate the compressor (fused) through a fused relay.

MainePorsche

Well, changed the ground point for pin 4. Actually easier for me to run it to the battery NEG via my pigtail connection for the maintainer. Result was the same anomalous function.
What to do now.
New controller from Greg or fabbing a fused switch through a relay to power the compressor when the lights are on ?

GregBBRD

Notes in blue, above.

Alan

Well - its resolder all the ground connection on the current unit or try a new unit or take Greg up on his offer of testing, but it seems now you pretty much know the unit is bad.

My point on the diodes was that they don't really fit this failiure mode either open circuit or short circuit.

While diodes commonly can fail into both states - overcurrent usually causes opens and high voltage stress more commonly causes shorts. Given that most of these are used as reverse biased protection devices if they fail shorted they will see a low impedance source (usually a switch to a 12v rail sinking through them to ground) - so they will then experiance a very high current. For diodes of this small size their maximum capacity when shorted usually means they will end up as an open circuit even if they start out as a short circuit - as the small semiconductor material or wire bonds will melt under high current stress.

Of course they may blow a fuse first or damage a switch. There are a few diodes that have other fiunctioons and failures in these will affect functionality differently.

Alan

MainePorsche

Greg, Thank you for your offers. I will speak to you soon about one of your units to replace with.

Considerable Thanks Alan for all you help with this matter.
Craig

Lorenfb

"While diodes commonly can fail into both states - overcurrent usually causes opens and high voltage stress more commonly causes shorts."

Actually, not totally correct!

1. At a certain excessive current, the diode will fail shorted.
Once the current exceeds another value, the diode usually
will burn and become open. In many cases the current
never reaches a value to burn 'open' the diode.
2. As in above, excessive voltage may result in a short initially
and then burn open as the current becomes overly excessive.

Again, most diodes fail in the shorted condition.

GregBBRD

I'm certainly not an electrical wizard, while Loren certainly is. He fixes a wide variety of electrical components. I fix one.

I have figured out how to test and repair the HVAC units....mostly because I needed to....not because I wanted to. It's a far cry from my favorite activity! I don't understand what is happening at every solder junction....like an electrical wizard can. I rely on my test board to tell me if things are working properly.

And if it smokes when I hook it up....I've figured out that is bad.

MainePorsche

Well Guys,
I'm not stumped, but I am at an impasse. After literally years of chasing this Gremlin, I am going to replace the controller with a Greg Brown tested unit. I have put up with having no compressor engagement when my headlights are turned on for long enough.

After evaluating every electrical system in the car even remotely to the headlights, AC system, Black/Blue illumination system, and alternator and power harnesses, I can not repair this. I must say in zealously tracking this Gremlin, I have learned quite a bit, and have done significant upgrades to these systems so actually I don't feel that bad about it. I would have liked to have killed the beast, but alas it has eluded me.

Pulled the controller this evening and began testing Track 4, the ground track. Track 4 has continuity through it out its course. Therefore one of the many diodes connected to it has a fault. I was prepared to go after the faulty diode(s), but when actually on the board this would require a significant dissection of the board's infrastructure. Also, testing the many diodes and their interelatedness to so many tracks I felt was beyond me. I feel somewhat proud that I came up with the diagnosis that was confirmed by Alan, but this is the end. I do feel bad about all the good LED and monofilament fiberoptic work that I had done, but I can relatively easily transfer this over to the new unit.

To all who have responded to my several threads regarding this issue, THANK YOU.

A special THANK YOU to Alan, who has been patient, cordial, and mentoring during this process.

Craig