AC Running Constantly - Relay?
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Racer
Joined: Oct 2012
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From: Middletown, New Jersey
AC Running Constantly - Relay?
I wonder if you guys could possibly help me with this. My car's (1991 S4 Auto) AC seems to run constantly regardless of whether it is turned on or off. Mechanic tells me that the compressor is always running. I thought it might be the relay inside the head unit. Am I on the right track with this? What else could be a likely culprit?
Part II of Question
I believe 1990+ models have a different head unit. Assuming that I need to swap the relay, is there anything specific to 1991 models that I should be aware of? I looked through past posts and found a great write-up on how to swap the relay with a relay from Radio Shack. Would these directions also apply to a 1991?
The AC blows ice cold. Great for the summer but I don't want anything freezing up for the winter. Thanks in advance for any help you can provide.
Frank
Part II of Question
I believe 1990+ models have a different head unit. Assuming that I need to swap the relay, is there anything specific to 1991 models that I should be aware of? I looked through past posts and found a great write-up on how to swap the relay with a relay from Radio Shack. Would these directions also apply to a 1991?
The AC blows ice cold. Great for the summer but I don't want anything freezing up for the winter. Thanks in advance for any help you can provide.
Frank
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There really is not an "Off" setting for the fan motor. If you have the bottom slider on the HVAC unit all the way to the left then you are on, if you have it on the square with the A/C button pushed in, you have A/C on. The fan never turns off.
Now if your A/C button is not pushed in and the compressor runs in all positions you either have a suck relay (head unit) or someone has played with the wiring on the car.
Try moving the bottom slider to the up/down arrows or the down arrow with the A/C button off, you should have normal non A/C airflow.
Now if your A/C button is not pushed in and the compressor runs in all positions you either have a suck relay (head unit) or someone has played with the wiring on the car.
Try moving the bottom slider to the up/down arrows or the down arrow with the A/C button off, you should have normal non A/C airflow.
Electron Wrangler
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If the car is in recirculate mode (or DEF mode) the AC will be on all the time - regardless of the AC button.
Most people have no idea of this.
Of course it could be that the relay contacts are just stuck on also... check...
Alan
Most people have no idea of this.
Of course it could be that the relay contacts are just stuck on also... check...
Alan
Last edited by Alan; Aug 23, 2013 at 11:27 AM.
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If the car is in recirculate mode (or DEF mode) the AC will be on all the time - regardless of the AC button. if the temperature slider is in the max cooling (minimum temp) the AC will be on all the time - regardless of the AC button. Most people have no idea of this.
Of course it could be that the relay contacts are just stuck on also... check...
Alan
Of course it could be that the relay contacts are just stuck on also... check...
Alan
Clarify. When you say 'AC will be on', are you saying the compressor is activated ? I've not noted a temperature change, that would lead me to believe the 'AC is on' unless I active the AC button. I've noted on the controller rheostat the little red button at the extremes of temp selection. Actually I was waiting for an opportunity to ask you what their function is.
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On a '91 model, the HVAC has the recirculation mode on the far left of the slider ****.
"Off" is actually the second position on the switch......I think it is a "rectangular" box.
This change, in 1991,"tricks" a lot of people.
"Off" is actually the second position on the switch......I think it is a "rectangular" box.
This change, in 1991,"tricks" a lot of people.
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The rectangle position is as usual just an airflow flap position - it is the center console & door vent only position. The center & door vents are actually always enabled (can be individually manually closed) - but in the other three flap positions you also get: the defroster vents, the footwell vents or both at the same time..
DEF is of course a special case (sets defroster flap position - but also controls max heat setting, AC on and max fan).
Since Recirculate is placed like a flap position - its not clear what airflow flaps you get with this. I think its unfortunate Porsche selected that in recirculate you always get defroster flap position - this actually reduces the flow to the center console vents whenever you switch to recirculate from vent only mode.
Recirculate is usually the most effective absolute cooling option. But since direct airflow causes skin evaporation and makes us feel cooler this means that although recirculate cools the car the fastest - it simply doesn't feel that way to the inhabitants and the non-recirculate in vent only mode directed right at you (with higher airflow) will usually feel cooler even though it really isn't.
Alan
Last edited by Alan; Aug 25, 2013 at 12:45 PM.
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