Predator's wrist nuke device for a climate control )

I'm pretty sure nobody had, has or will ever have such a problem, but, anyway, I'll share it just because why not. This story even has a happy end - well, kinda.
So.
This is what Predator had on his wrist:



And this is what my climate control looked like sometimes:




Like so many of us, I had HVAC control resistors soldering gone bad. After several attempts of soldering existing resistors back in their places, I decided I had enough of uncertainty, I was just never sure what caused HVAC glitches - my bad soldering, or resistor overheating, or something else. So I came up with an overkill solution - replaced 4 little resistors with a couple of beefy ones.



Overheating of resistors or loose soldering doesn't bother me anymore, but still, climate control didn't work as it should. Or, rather, it did work as it definitely shouldn't. Every day, after 30~60 minutes of flawless operation, my climate control would start to acting up - random, chaotic beeps, fan speed changes, display flashing and anything in between, including that "Predator display mode". Sometimes it even was impossible to turn the damn thing off - it just came back on by itself, with all the glitches.  Needless to say, it was annoying as hell, I was nervous any time I had to ride for more than an hour. And worst of all - I had no idea why all this was happening. I couldn't find symptoms like mine anywhere on the Internet. Code scanner didn't show anything. Of course, my first guess (and, actually, the only guess) was intermittent contact somewhere, but where and which one? The most obvious thing to check was the power, and I ruled it out by connecting reliable +12V and ground both to the climate control unit and HVAC programmer. Nothing changed.
At some point (soon enough) I found myself desperate and out of ideas, and we (I and my wounded pride) finally went to a shop. My buddy car tech guy with long beard of knowledge and shiny bald head spent more than an hour meditating over diagrams and poking here and there in the passenger foot well. Oh, BTW - that particular day my climate control was working just fine, no glitches whatsoever, so we couldn't reproduce the problem. Somehow, I wasn't surprised. Cars, you know. They do that. )
There were several different things we tested and checked, but this is what finally did the trick: my car guru removed dark green wire from C4 cavity of the wider connector on the HVAC programmer. This wire is a diagnostic signal, and with this wire gone I won't be able to read HVAC system with a diagnostic tools. Not a big loss - after all, I never needed it in my 3 years of ownership, and in the moment of need it didn't help me anyway. The idea was that SOMETHING was sending chaotic, rubbish signals to the digital line, causing HVAC programmer to go bonkers. Turned out this was exactly what was happening to my climate control, and, although I still don't know what that SOMETHING is, I'm so happy my system is working normally now. Currently I have no plans on hunting that SOMETHING down, but may be some day I will.


Just in case - a page from the FSM:

The real problem here is that you eliminated the resisitor network. THere is a version of this board that is wired as you shouw but it's not intended for the Riviera. Let me explain.

A resistor network is a combination of several resistors that are configured into a pattern. The resistors in a network act as voltage dividers which divide the voltage that is applied to a circuit into smaller amounts. One common use of a resistor network is to pull multiple lines up or down, in general on a data bus (BIG HINT - the diagnostic signal). Replacing the resistor network with a single resistor would short all of the lines in the bus together, making it not work at all. I'd have to pull my board and look at it closely to say for sure if that is a factor with this control circuit.

Also, resistor networks are used when it helps costs. Sometimes, for relatively long manufacturing runs (HINT: the Riviera, and the LeSabre and the Park Avenue over some number of years) machine assembly placement of a custom component might cost say 5 cents. A resistor in an array might cost less than one cent. So in this toy example one network saves about 10 cents, which translates to a substantial difference in serial (mass) production - perhaps tens of thousands of dollars. So - the main advantage of a resistor network is space and time. There may be other functional characteristics involved depending on the overall circuit design.

When I replaced my resistors (if you drive your Riv long enough you will have to repair or replace the resistors in the HVAC control head) I looked on line and found I could get the exact same ones from DigiKey. I figured there was no sense in duplicating the overheat problem, so I upgraded them to Riedon UB5C-120RF1 resistors that were about the same length but had much better current capacity. The upgrades cost a lot more than the originally spec'd units, but not prohibitively. They currently are 88c each, 78.2c each in quantity 10 (10 is the first quantity-price break). They *just* fit, you have to fold the leads back under the resistors in a stairstep shape -- I used a notched solder-aid tool to make those tight little bends. That reminds me, I have to replace that tool... The cut sheet and brochure mentions what applications the Riedons were generally intended for and this HVAC head application kind of fits.

By the way, a nice unit for illuminating the power point cavity on the passenger side of the console, or replacing the little floodlights in the door pulls, is Digi Key 5110F5-12V-ND. They are now $2.24 each, or $1.99 each in quantity 10.

Gotta run

Albertj