A/C experts, how much does the DME control?
06-12-2011, 10:51 AM
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A/C experts, how much does the DME control?
I'm just curious what control the DME has over the A/C system? IE does it turn off the compressor at high rpm? Does it have any control over how often the compressor cycles? Or is the compressor on whenever the snowflake button is on?
I found the required pinouts over on 944hybrids so I know how to tap into the A/C signal, however I don't want to just use an On/Off switch if that's not how Porsche designed the system. I'll keep the DME if required, but I'd rather just get rid of it.
Any help would be appreciated.
I found the required pinouts over on 944hybrids so I know how to tap into the A/C signal, however I don't want to just use an On/Off switch if that's not how Porsche designed the system. I'll keep the DME if required, but I'd rather just get rid of it.
Any help would be appreciated.
06-12-2011, 12:08 PM
#3
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I have been wondering if the DME turns off the rad fans once vehicle speed exceeds ~ 35 mph. Most modern systems do (with temperature override).
Not seeing anything useful at frwilk's site.
Not seeing anything useful at frwilk's site.
06-12-2011, 12:35 PM
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If you look here (one of Wilk's sites) http://www.the944.com/
you can see the Pin-out on the late DME that appears to control the AC...I did not dig further to find out just how it works but there is a control.....
you can see the Pin-out on the late DME that appears to control the AC...I did not dig further to find out just how it works but there is a control.....
06-12-2011, 01:07 PM
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Pin 13 on the 14 pin connector on the drivers side engine compartment near the fuse block is the A/C control pin, what I would really like to know is how much control the DME has over the fans/compressor etc.
I don't have a radiator, so there is no parasitic heat to deal with, so I might get away with a smaller or lower speed fan, or with the stock fans I might have a better performing A/C system?
I've read that some cars turn off the A/C compressor at high rpms, and some adjust the engine rpm to compensate for A/C coming on. So I'm wondering if the A/C system needs any inputs to operate correctly. IE does it need an RPM/temperature signal or similar?
PS. the car in question was an '86NA
I don't have a radiator, so there is no parasitic heat to deal with, so I might get away with a smaller or lower speed fan, or with the stock fans I might have a better performing A/C system?
I've read that some cars turn off the A/C compressor at high rpms, and some adjust the engine rpm to compensate for A/C coming on. So I'm wondering if the A/C system needs any inputs to operate correctly. IE does it need an RPM/temperature signal or similar?
PS. the car in question was an '86NA
06-12-2011, 10:19 PM
#7
I think m73m75 is right. The DME only has to adjust for the added load of compressor on at idle (via idle speed control). It is possible that DME cuts power to compressor via full throttle signal from TPS but I'm not sure.
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06-12-2011, 11:34 PM
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On the 944 the AC is a "standalone" system. It requires no input from DME. On LTx or LSx conversion you have some options if you are going to run VSS. The major being turn off the fans above X, and if you get a really custome tune you can tell it to cut off the AC clutch and or the charging system at a certain throttle position or speed. I would not really recommed turning off the AC or charging based on throttle position or speed as it has a tendency to shock the AC clutch or spike voltage into your electrical.
The conversions i have done i fairly much left the AC stystem as designed. If you are running dual speed fan kick on the low speed when the AC system is engerized. Many people make the mistake and wire so only when the ac clutch is engaged the fan spins. With conversions I always tune to turn off the fans above 50 mph if it is mainly a street car.
The conversions i have done i fairly much left the AC stystem as designed. If you are running dual speed fan kick on the low speed when the AC system is engerized. Many people make the mistake and wire so only when the ac clutch is engaged the fan spins. With conversions I always tune to turn off the fans above 50 mph if it is mainly a street car.
06-12-2011, 11:46 PM
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Oh yean I forgot.
On converted 944's or any OBD2 car and most OBD1 you can tell it to raise the idle say from 700 to 750 when the AC is turned on. On a converted cars all you need is a wire back to the computer that tells it when the AC is on, normally 12v+
On converted 944's or any OBD2 car and most OBD1 you can tell it to raise the idle say from 700 to 750 when the AC is turned on. On a converted cars all you need is a wire back to the computer that tells it when the AC is on, normally 12v+
06-13-2011, 12:05 AM
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On the 944 the AC is a "standalone" system. It requires no input from DME. On LTx or LSx conversion you have some options if you are going to run VSS. The major being turn off the fans above X, and if you get a really custome tune you can tell it to cut off the AC clutch and or the charging system at a certain throttle position or speed. I would not really recommed turning off the AC or charging based on throttle position or speed as it has a tendency to shock the AC clutch or spike voltage into your electrical.
The conversions i have done i fairly much left the AC stystem as designed. If you are running dual speed fan kick on the low speed when the AC system is engerized. Many people make the mistake and wire so only when the ac clutch is engaged the fan spins. With conversions I always tune to turn off the fans above 50 mph if it is mainly a street car.
The conversions i have done i fairly much left the AC stystem as designed. If you are running dual speed fan kick on the low speed when the AC system is engerized. Many people make the mistake and wire so only when the ac clutch is engaged the fan spins. With conversions I always tune to turn off the fans above 50 mph if it is mainly a street car.
Here is a lame *** video of my testing.
http://www.youtube.com/watch?v=H2eGL...er_profilepage
06-13-2011, 12:43 PM
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DME doesn't have anything to do with a/c compressor, it's all pretty much temperature controlled by switches...when you push the snowflake compressor is energized, and based on what temperature setting you have on the **** will cycle on and off..also low speed fans come on...there is a temperature switch on the hose connected to receiver drier that has a temperature switch which sense the temperature of the freon and at whatever temperature (hot)-it could also be pressure based switch...it kicks on the high speed fans.. not all cars have this switch..but i will tell you that there a 2 different part numbers and one is $100 and the other is $250....if you notice your high speed fans clicking on and off shortly after you have a/c switched on you need a new temperature switch, after a short while after suffiecient temperature or pressure will keep the high speed fans on til you turn off snowflake switch..Believe me I've done some investigating on this a/c system being that today it is supposed to be 108 degress..
