HVAC Circuit Board Question
10-03-2012, 01:23 AM
#1
Nordschleife Master
Thread Starter
HVAC Circuit Board Question
Guys (especially electrical wizards),
Here's my gremlin:
AC system (I know, bare with me it's interesting) works perfectly in all aspects EXCEPT when I turn the headlight switch on to position 1 or 2. When I do this, the compressor disengages if the AC was ON, or it won't engage if AC was OFF.
Here's what I've done:
Diligently went through the normal systems checks under the guidance of Alan (very detailed connector pin and CE evaluation), Wally, Stan. With lights off ALL systems along AC power route normal. Removed PO remote door opener and alarm diligently for there was an invasion into the headlight switch output. Sound system Alpine and done very well - no intrusion into Black/Blue illumination system. No intrusion at CE Panel as well. Every wire (under console and pod), every ground, inspected, tested and all the way they should be. Headlight switch new - all in it function normally.
Here's what's interesting and where I think the problem resides:
One night driving home, I hit a small bump and the center console goes dark. Pod still illuminated along with the warning panel with AC switch and locking button. Everything on the center console had retained its function (ie clock , HVAC unit, cigarette lighter). Got home and just peaked and found one of the two connectors from the potentiometer (rheostat) popped off. I then said Hmmm and turned on the AC with the headlight switch turned ON and the compressor engaged ! Reconnected the Black/Blue and the AC (compressor) would NOT engage.
Now (from prior testing) pin 3 (Black/Blue) and 4 (Ground) tested out with expected results and illumination works fine in the unit with with AC button engaged except no compressor engagement.
So, here's what we have so far:
AC system fine from relay (functions normally with lights OFF) to compressor.
When pin 3 (Black/Blue) has no current, AC system function normally with lights ON and OFF.
Now here's some extras:
When pin 3 is pulled off from connecting with the Board compressor does NOT ENGAGE AT ALL. This I find odd.
I ran a separate lines to the HVAC bulb replacing the Brown and Blk/Blue connections to the Board. This was connected to the rheostat output. Result is HVAC illuminates like normal turning light switch on, but it is not connected via the Board to pins 3 and 4. HVAC still functions ABNORMALLY with lights on. If I leave bulb connected like this and unplug pin 3 connection to the Board, AC doesn't function at all.
This tells me that the issue is on the ground side of the bulb. According to the WD, pin 3 goes no where else but to bulb POS. From the bulb, line goes to pin 4 BROWN and THEN to a diode. I'm not really sure what the function of a diode is (supposed to limit direction of current ?), but Guys, if this diode were to 'fail' could this be the issue ? If the diode failed and didn't limit current down the line, it looks like it interacts with the internal relay, if I read the WD correctly. I see no gross anomalies on the Board, and with all I've done and experimented with I think this is where the problem is.
Tell me your thoughts on review. I tried to be as clear as I could, but feel free to ask for clarification. I would rather change out a diode than the whole controller (then my next question would be what diode to replace with).
Really, Thanks in Advance
Craig
Here's my gremlin:
AC system (I know, bare with me it's interesting) works perfectly in all aspects EXCEPT when I turn the headlight switch on to position 1 or 2. When I do this, the compressor disengages if the AC was ON, or it won't engage if AC was OFF.
Here's what I've done:
Diligently went through the normal systems checks under the guidance of Alan (very detailed connector pin and CE evaluation), Wally, Stan. With lights off ALL systems along AC power route normal. Removed PO remote door opener and alarm diligently for there was an invasion into the headlight switch output. Sound system Alpine and done very well - no intrusion into Black/Blue illumination system. No intrusion at CE Panel as well. Every wire (under console and pod), every ground, inspected, tested and all the way they should be. Headlight switch new - all in it function normally.
Here's what's interesting and where I think the problem resides:
One night driving home, I hit a small bump and the center console goes dark. Pod still illuminated along with the warning panel with AC switch and locking button. Everything on the center console had retained its function (ie clock , HVAC unit, cigarette lighter). Got home and just peaked and found one of the two connectors from the potentiometer (rheostat) popped off. I then said Hmmm and turned on the AC with the headlight switch turned ON and the compressor engaged ! Reconnected the Black/Blue and the AC (compressor) would NOT engage.
Now (from prior testing) pin 3 (Black/Blue) and 4 (Ground) tested out with expected results and illumination works fine in the unit with with AC button engaged except no compressor engagement.
So, here's what we have so far:
AC system fine from relay (functions normally with lights OFF) to compressor.
When pin 3 (Black/Blue) has no current, AC system function normally with lights ON and OFF.
Now here's some extras:
When pin 3 is pulled off from connecting with the Board compressor does NOT ENGAGE AT ALL. This I find odd.
I ran a separate lines to the HVAC bulb replacing the Brown and Blk/Blue connections to the Board. This was connected to the rheostat output. Result is HVAC illuminates like normal turning light switch on, but it is not connected via the Board to pins 3 and 4. HVAC still functions ABNORMALLY with lights on. If I leave bulb connected like this and unplug pin 3 connection to the Board, AC doesn't function at all.
This tells me that the issue is on the ground side of the bulb. According to the WD, pin 3 goes no where else but to bulb POS. From the bulb, line goes to pin 4 BROWN and THEN to a diode. I'm not really sure what the function of a diode is (supposed to limit direction of current ?), but Guys, if this diode were to 'fail' could this be the issue ? If the diode failed and didn't limit current down the line, it looks like it interacts with the internal relay, if I read the WD correctly. I see no gross anomalies on the Board, and with all I've done and experimented with I think this is where the problem is.
Tell me your thoughts on review. I tried to be as clear as I could, but feel free to ask for clarification. I would rather change out a diode than the whole controller (then my next question would be what diode to replace with).
Really, Thanks in Advance
Craig
Last edited by MainePorsche; 10-06-2012 at 04:27 PM.
10-03-2012, 01:08 PM
#2
Nordschleife Master
Thread Starter
Now here's some extras:
When pin 3 is pulled off from connecting with the Board compressor does NOT ENGAGE AT ALL. This I find odd.
I ran a separate lines to the HVAC bulb replacing the Brown and Blk/Blue connections to the Board. This was connected to the rheostat output. Result is HVAC illuminates like normal turning light switch on, but it is not connected via the Board to pins 3 and 4. HVAC still functions ABNORMALLY with lights on. If I leave bulb connected like this and unplug pin 3 connection to the Board, AC doesn't function at all.
This tells me that the issue is on the ground side of the bulb. According to the WD, pin 3 goes no where else but to bulb POS. From the bulb, line goes to pin 4 BROWN and THEN to a diode. I'm not really sure what the function of a diode is (supposed to limit direction of current ?), but Guys, if this diode were to 'fail' could this be the issue ? If the diode failed and didn't limit current down the line, it looks like it interacts with the internal relay, if I read the WD correctly. I see no gross anomalies on the Board, and with all I've done and experimented with I think this is where the problem is.
If diode 'failed' on ground side of the controller bulb, thus compromising ground through pin 4, wouldn't I get an anomalous reading when testing the specific ground ? But I did not find this to be the case, hence this is not the problem.
The issue of the HVAC controller functioning normally when pin 3 has no current, and it functioning even more abnormally when pin 3 is disconnected from the Board (no AC lights on or OFF), is perplexing.
Some have said just get a new relay for the Board.
I am concerned about doing this for I still think there is an anomaly on the the Board. I've visually inspected this, and nothing is obvious to my eye.
10-03-2012, 01:34 PM
#3
Electron Wrangler
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Well - interesting - still struggling with this gremlin...
Based on what you have done - I'd say your ground on pin 4 is probably not good either at the pin or internally on the board. Most likely its internal to the head unit or affecting the head unit wire only because if the rest of what is connected outside the unit to that pin didn't have a good ground - you would have far bigger problems.
Initially maybe you can try just a temporary solution connected to the cathodes of those diodes..
Or try measuring resistance from the HVAC headunit pin 4 to the realy coil pin.
BTW the diodes are reversed biased to ground to protect against negative switching spikes on the contacts (from downstream inductance - clutch coil/solenoids).
The reason this works is that pin 3 is effectively 'grounded' though all the other (off/cold) illumination bulb filaments when the light switch is off, for the relay coil alone the resistance of the cold filament of the bulb in the headunit is also very small (1/10 of what you'd think base on its ratings) and it can provide a good enough ground to the relay coil - but when the lights are on - nothing.
I think this will be the cause - very good diagnostics here - what you posted makes this much clearer. If only everyone was so thorough/detailed.
Alan
Based on what you have done - I'd say your ground on pin 4 is probably not good either at the pin or internally on the board. Most likely its internal to the head unit or affecting the head unit wire only because if the rest of what is connected outside the unit to that pin didn't have a good ground - you would have far bigger problems.
Initially maybe you can try just a temporary solution connected to the cathodes of those diodes..
Or try measuring resistance from the HVAC headunit pin 4 to the realy coil pin.
BTW the diodes are reversed biased to ground to protect against negative switching spikes on the contacts (from downstream inductance - clutch coil/solenoids).
The reason this works is that pin 3 is effectively 'grounded' though all the other (off/cold) illumination bulb filaments when the light switch is off, for the relay coil alone the resistance of the cold filament of the bulb in the headunit is also very small (1/10 of what you'd think base on its ratings) and it can provide a good enough ground to the relay coil - but when the lights are on - nothing.
I think this will be the cause - very good diagnostics here - what you posted makes this much clearer. If only everyone was so thorough/detailed.
Alan
Last edited by Alan; 10-03-2012 at 01:53 PM.
10-03-2012, 01:43 PM
#4
Nordschleife Master
Thread Starter
Well - interesting - still struggling with this gremlin...
Based on what you have done - I'd say your ground on pin 4 is probably not good either at the pin or internally on the board. Most likely its internal to the head unit or affecting the head unit wire only bacause if the rest of what is connected outside the unit to that pin didn't have a good ground - you would far bigger problems.
Initially maybe you can try just a temporary solution connected to the cathodes of those diodes..
BTW the diodes are reversed biased to ground to priotect against negatuive swuitching spoikes on the contacts (form downstream inductance - clutch coil/solenoids).
Alan
Based on what you have done - I'd say your ground on pin 4 is probably not good either at the pin or internally on the board. Most likely its internal to the head unit or affecting the head unit wire only bacause if the rest of what is connected outside the unit to that pin didn't have a good ground - you would far bigger problems.
Initially maybe you can try just a temporary solution connected to the cathodes of those diodes..
BTW the diodes are reversed biased to ground to priotect against negatuive swuitching spoikes on the contacts (form downstream inductance - clutch coil/solenoids).
Alan
So could/would one of your recommendations be to not simply change out the internal relay, but to get a new Board (controller) ? This what I'm taking from the above.
10-03-2012, 01:48 PM
#5
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No I think its likely still quite repairable - resolder all the connections on the traces connected to Pin 4...
First test it this with an ohmmeter - may narrow this down even further...
Seems clear to me that the relay actually works fine...
Alan
First test it this with an ohmmeter - may narrow this down even further...
Seems clear to me that the relay actually works fine...
Alan
10-03-2012, 01:53 PM
#6
Nordschleife Master
Thread Starter
Ok Alan. Will be done.
I'm hoping to report back to you next time with Resolution.
The positive about this is that I'm happy with my progression in learning/handling electrical matters on the car.
Craig
I'm hoping to report back to you next time with Resolution.
The positive about this is that I'm happy with my progression in learning/handling electrical matters on the car.
Craig
10-03-2012, 02:51 PM
#7
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The individual diodes are easy to check with an ohm meter. I "find" bad ones quite frequently and have "donor" boards that I steal them from.
In terms of being able to "logic" that circuit to figure out your "individual" problem....that's way over my head.
In terms of being able to "logic" that circuit to figure out your "individual" problem....that's way over my head.
__________________
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714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
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greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Trending Topics
10-03-2012, 03:01 PM
#8
Nordschleife Master
Thread Starter
Thanks Greg. Maybe I'll speak to you soon about a replacement diode, but I know I will about fuel lines etc.. .
10-03-2012, 03:16 PM
#9
Electron Wrangler
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I think your diodes are probably OK - if they did test out bad the specs on these diodes are not at all critical - just get diodes rated for at least 2A with PIV of at least 30V and you will be fine.
Radio Shack or Fry's Electronics will have plenty of choices.
Example : 1N5406 3A 600V All Electronics - 5 for $1
Alan
Radio Shack or Fry's Electronics will have plenty of choices.
Example : 1N5406 3A 600V All Electronics - 5 for $1
Alan
10-06-2012, 04:25 PM
#11
Nordschleife Master
Thread Starter
Final Update
To All and especially The Venerable Alan,
I can go no further.
I wrestled with this gremlin since 2008, three years before joining Rennlist. I have done a great deal of diagnostic and repair work (flying solo without Rennlist) as a result of this gremlin. My car is better for it, and so am I. Since joining Rennlist, my progress has been exponential in finally diagnosing it. I want to Thank all who have had contributed to what I think is my success in this matter. Special mention to Alan, Wally, and Stan. I feel it is a success in that I have gotten to the root cause of the problem. I attempted today to finish it, but I could not. I had removed the HVAC controller to inspect, and repair the defect on the board. Nothing obvious along the traces from pin 4 (and pin 3) for me to address. Along the ground pin 4 trace there were a great many diodes. Many I could not reach to test or repair without taking the support infrastructure off for the rheostat. I felt the potential for breaking this was to far to go to POTENTIALLY find the faulty diode. I am going to use the advice my favorite uncle gave me when I was crestfallen at 16 when my girlfriend broke up with me. He simply said chin up, go out and get another one ! That is what I am going to do, go get another controller and put an end to this. Don't worry I won't send it back for core exchange so someone else can catch the bug. I think I'll make a little show piece of it in the garage. Thanks Again.
Craig
I can go no further.
I wrestled with this gremlin since 2008, three years before joining Rennlist. I have done a great deal of diagnostic and repair work (flying solo without Rennlist) as a result of this gremlin. My car is better for it, and so am I. Since joining Rennlist, my progress has been exponential in finally diagnosing it. I want to Thank all who have had contributed to what I think is my success in this matter. Special mention to Alan, Wally, and Stan. I feel it is a success in that I have gotten to the root cause of the problem. I attempted today to finish it, but I could not. I had removed the HVAC controller to inspect, and repair the defect on the board. Nothing obvious along the traces from pin 4 (and pin 3) for me to address. Along the ground pin 4 trace there were a great many diodes. Many I could not reach to test or repair without taking the support infrastructure off for the rheostat. I felt the potential for breaking this was to far to go to POTENTIALLY find the faulty diode. I am going to use the advice my favorite uncle gave me when I was crestfallen at 16 when my girlfriend broke up with me. He simply said chin up, go out and get another one ! That is what I am going to do, go get another controller and put an end to this. Don't worry I won't send it back for core exchange so someone else can catch the bug. I think I'll make a little show piece of it in the garage. Thanks Again.
Craig
10-06-2012, 05:29 PM
#12
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To All and especially The Venerable Alan,
I can go no further.
I wrestled with this gremlin since 2008, three years before joining Rennlist. I have done a great deal of diagnostic and repair work (flying solo without Rennlist) as a result of this gremlin. My car is better for it, and so am I. Since joining Rennlist, my progress has been exponential in finally diagnosing it. I want to Thank all who have had contributed to what I think is my success in this matter. Special mention to Alan, Wally, and Stan. I feel it is a success in that I have gotten to the root cause of the problem. I attempted today to finish it, but I could not. I had removed the HVAC controller to inspect, and repair the defect on the board. Nothing obvious along the traces from pin 4 (and pin 3) for me to address. Along the ground pin 4 trace there were a great many diodes. Many I could not reach to test or repair without taking the support infrastructure off for the rheostat. I felt the potential for breaking this was to far to go to POTENTIALLY find the faulty diode. I am going to use the advice my favorite uncle gave me when I was crestfallen at 16 when my girlfriend broke up with me. He simply said chin up, go out and get another one ! That is what I am going to do, go get another controller and put an end to this. Don't worry I won't send it back for core exchange so someone else can catch the bug. I think I'll make a little show piece of it in the garage. Thanks Again.
Craig
I can go no further.
I wrestled with this gremlin since 2008, three years before joining Rennlist. I have done a great deal of diagnostic and repair work (flying solo without Rennlist) as a result of this gremlin. My car is better for it, and so am I. Since joining Rennlist, my progress has been exponential in finally diagnosing it. I want to Thank all who have had contributed to what I think is my success in this matter. Special mention to Alan, Wally, and Stan. I feel it is a success in that I have gotten to the root cause of the problem. I attempted today to finish it, but I could not. I had removed the HVAC controller to inspect, and repair the defect on the board. Nothing obvious along the traces from pin 4 (and pin 3) for me to address. Along the ground pin 4 trace there were a great many diodes. Many I could not reach to test or repair without taking the support infrastructure off for the rheostat. I felt the potential for breaking this was to far to go to POTENTIALLY find the faulty diode. I am going to use the advice my favorite uncle gave me when I was crestfallen at 16 when my girlfriend broke up with me. He simply said chin up, go out and get another one ! That is what I am going to do, go get another controller and put an end to this. Don't worry I won't send it back for core exchange so someone else can catch the bug. I think I'll make a little show piece of it in the garage. Thanks Again.
Craig
or
If you'd like to eliminate the "surrounding vehicle", I'd be happy to send you a known good unit, for you to plug into your car.
10-06-2012, 08:58 PM
#13
Nordschleife Master
Thread Starter
I have a complete test board that I test all my rebuilt units on....I'd be more than happy to put it on my board and run it through a complete cycle.
or
If you'd like to eliminate the "surrounding vehicle", I'd be happy to send you a known good unit, for you to plug into your car.
or
If you'd like to eliminate the "surrounding vehicle", I'd be happy to send you a known good unit, for you to plug into your car.
I'm going to take you up on that.
Thanks
10-07-2012, 05:22 AM
#14
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Which one? Or both?
Might make sense for me to send you a known good unit that you can plug into your car. If that fixes the problem, you can then send me your unit and I can plug it onto my "test" board and see if I can figure out what is wrong.
Whatever you want to do. I'd just like to see you fix this "ongoing" problem, with your car.
Might make sense for me to send you a known good unit that you can plug into your car. If that fixes the problem, you can then send me your unit and I can plug it onto my "test" board and see if I can figure out what is wrong.
Whatever you want to do. I'd just like to see you fix this "ongoing" problem, with your car.
10-07-2012, 12:07 PM
#15
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I doubt it is a diode (any of them really). 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.
I think its the ground to the unit - and this may be an issues outside the unit - so there is a risk that even a new unit won't solve this.
I'd either get yours tested by Greg first - or ensure you do indeed have a good connection on the ground pin #4 as it enters the board.
Narrowing down the solution on the board - you really need to just ensure that the realy coil has a good ground... I'm certain this is the isues but it could inside the HVAC or outside in the feed to it.
Externally you could just connect a small bulb from +12v to the external Pin 4 connector and see if it lights (compare brightness Vs. a good ground at the ground point).
Hate to see you get a new HVAC head unit and have the same exact symptoms...
Alan
I think its the ground to the unit - and this may be an issues outside the unit - so there is a risk that even a new unit won't solve this.
I'd either get yours tested by Greg first - or ensure you do indeed have a good connection on the ground pin #4 as it enters the board.
Narrowing down the solution on the board - you really need to just ensure that the realy coil has a good ground... I'm certain this is the isues but it could inside the HVAC or outside in the feed to it.
Externally you could just connect a small bulb from +12v to the external Pin 4 connector and see if it lights (compare brightness Vs. a good ground at the ground point).
Hate to see you get a new HVAC head unit and have the same exact symptoms...
Alan