Problem with rear AC fan control
05-06-2007, 12:43 AM
#1
Nordschleife Master
Thread Starter
Problem with rear AC fan control
The AC on my car is not functioning as it should. It just simply does not blow cold at all. I havent really bothered to have the system's coolant level tested as I assume that to be the issue but am really uncertian.
That being said, I also noticed a few weeks back, that the rear fan **** for the rear AC does nothing until it reaches the maximum fan speed. Similiar to the issue with the relay for the main AC unit. I am wondering if a single electrical issue could have cause both faults?
Ive never heard of the rear AC fan control not working before, but i am sure someone has experienced it once before. What could this be, any ideas? I am beginning to wonder if the AC not blowing cold and the rear AC fan control are connected. They both stopped suddenly and presumeably at or around the same time. Possibly a compressor clutch control problem? I dont know why this would then limit the rear fan speed but perhaps it does.
I had also noticed once before when i had an AC issue, that when i pressed the AC button, it would not illuminate. If the clutch does not engage would the light go on? Right now the car isnt running due to the fuel pump being replaced so i cant tell if the compressor runs when you press the switch.
Any ideas here, could this be a simple relay problem? I thought there was an AC relay but looking on my fuse chart i see only an AC fuse but no relay for my 1990 MY car.
Thanks in advance
That being said, I also noticed a few weeks back, that the rear fan **** for the rear AC does nothing until it reaches the maximum fan speed. Similiar to the issue with the relay for the main AC unit. I am wondering if a single electrical issue could have cause both faults?
Ive never heard of the rear AC fan control not working before, but i am sure someone has experienced it once before. What could this be, any ideas? I am beginning to wonder if the AC not blowing cold and the rear AC fan control are connected. They both stopped suddenly and presumeably at or around the same time. Possibly a compressor clutch control problem? I dont know why this would then limit the rear fan speed but perhaps it does.
I had also noticed once before when i had an AC issue, that when i pressed the AC button, it would not illuminate. If the clutch does not engage would the light go on? Right now the car isnt running due to the fuel pump being replaced so i cant tell if the compressor runs when you press the switch.
Any ideas here, could this be a simple relay problem? I thought there was an AC relay but looking on my fuse chart i see only an AC fuse but no relay for my 1990 MY car.
Thanks in advance
05-06-2007, 04:43 PM
#3
Nordschleife Master
Thread Starter
I agree with you that i dont see why the rear control would affect the entire system. But they seem to have stopped working at or around the same time. They probably have nothing to do with one another.
Does the rear fan switch use that coil type deal that the main fan control uses. Where in sometimesthey only work when set to level 4 when it then bypass's the coils and just blows? Does the rear fan use a similiar setup?
Does the rear fan switch use that coil type deal that the main fan control uses. Where in sometimesthey only work when set to level 4 when it then bypass's the coils and just blows? Does the rear fan use a similiar setup?
05-26-2008, 03:47 PM
#4
Nordschleife Master
Thread Starter
UPDATE:
After buying a new fan control switch and plugging it in and having no change I looked towards something else. Like the Resistor which controls the main head unit fan speed. When this is out of whack it will only work on level 4. So i figured there maybe something like this which controls the rear fan and i see PN 928 618 137 00.
I had thought I would just get one of those and call it a day but the other night when i was playing in the CE panel i decided to pull the AC relay and wanted to replace it with a new relay that i had bought some time ago as a spare. Well did end up pulling it and also pulled "relay X" Once I installed the new relay in the X position i then had the front HU working on all 4 fan speeds and the rear one returned to full function as well.
This seems very odd to me, can anyone explain how these systems work. Could a relay or loose contact in the CE panel be the source of my problems?
Shortly after doing this I went for a drive and sometime in that drive the rear fan went back to working only on its highest setting. I want to eliminate this inconsistency once and for all.
Ideas?
After buying a new fan control switch and plugging it in and having no change I looked towards something else. Like the Resistor which controls the main head unit fan speed. When this is out of whack it will only work on level 4. So i figured there maybe something like this which controls the rear fan and i see PN 928 618 137 00.
I had thought I would just get one of those and call it a day but the other night when i was playing in the CE panel i decided to pull the AC relay and wanted to replace it with a new relay that i had bought some time ago as a spare. Well did end up pulling it and also pulled "relay X" Once I installed the new relay in the X position i then had the front HU working on all 4 fan speeds and the rear one returned to full function as well.
This seems very odd to me, can anyone explain how these systems work. Could a relay or loose contact in the CE panel be the source of my problems?
Shortly after doing this I went for a drive and sometime in that drive the rear fan went back to working only on its highest setting. I want to eliminate this inconsistency once and for all.
Ideas?
05-26-2008, 06:54 PM
#5
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
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On some years the whole HVAC unit is supplied by the ignition (15) bus, or the X-Bus direct from the ignition switch and in some from the X-Bus repeater relay and in some others - like yours - by the Supply relay (its in possition X but this is a different - but similar - function to the X-relay).
Depending on what the source is for your year this must work to turn on the Front Blower Relay for all speeds. The DEF relay (for high speed fan in defogger mode) is independently controlled.
To your other questions - the rear AC is completely independant - is fed by direct ignition switched power -and has its own resistor pack that can fail in similar ways to the later versions of the front relay pack with similar effects (only high speed works - others just cut out).
From what you describe it sounds like the rear resistor pack is on the fritz...
The AC button light just indicates the swtich is on - it has no idea if the system is functioning correctly.
Alan
Depending on what the source is for your year this must work to turn on the Front Blower Relay for all speeds. The DEF relay (for high speed fan in defogger mode) is independently controlled.
To your other questions - the rear AC is completely independant - is fed by direct ignition switched power -and has its own resistor pack that can fail in similar ways to the later versions of the front relay pack with similar effects (only high speed works - others just cut out).
From what you describe it sounds like the rear resistor pack is on the fritz...
The AC button light just indicates the swtich is on - it has no idea if the system is functioning correctly.
Alan
Last edited by Alan; 05-26-2008 at 07:36 PM.
05-26-2008, 10:09 PM
#6
Nordschleife Master
Thread Starter
Thanks Alan
The rear resistor is what i suspect. When i drive it i am testing it out and i will click it on level 1 on the rear and it seems like it starts then does nothing till i click it all the way to full blower. So yeah its acting up.
I had no idea that the "X-relay" or mystery relay had anything to do with the HVAC blower. Its really odd how i found this, but now after 2 days and 4-5 trips in the car the blower is working on all levels everytime. I had never read about this in any HVAC posts and dont find this to be common knowledge.
What does the X-relay do? It sounds like it can do any number of things, i really thought it was just one of those weird coincidences that the main blower started to work, but maybe it is connected somehow as you suggest.
The rear resistor is what i suspect. When i drive it i am testing it out and i will click it on level 1 on the rear and it seems like it starts then does nothing till i click it all the way to full blower. So yeah its acting up.
I had no idea that the "X-relay" or mystery relay had anything to do with the HVAC blower. Its really odd how i found this, but now after 2 days and 4-5 trips in the car the blower is working on all levels everytime. I had never read about this in any HVAC posts and dont find this to be common knowledge.
What does the X-relay do? It sounds like it can do any number of things, i really thought it was just one of those weird coincidences that the main blower started to work, but maybe it is connected somehow as you suggest.
