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Does anybody know how the compressor runs normally in a C2 996 I'm having some issues and I'm

not sure if it is suppose to run all the time or if it short cycles and if it cycles what determines the time

run and time off ?  Weather here in Alabama as of late has been a little warm and its a shame to let

such a great car set in the garage because the air isn't working!





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My understanding is it doesn't cycle as it's a variable displacement design so it should stay ON whenever the a/c is turned ON. It varies it's displacement per the cooling demand. One exception is when you're close to redline, the DME will turn it OFF.

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Hi John,  


I'm no expert, but I'll tell you what little I know.  Your temp switch or dial is attached to a capallary tube which is embedded between the cooling fins of your condenser. 

The end of the tube is sensitive to temperature changes which turns on and off the compressor.  You can usually hear the compressor go on and off because the engine will change it's sound or sometimes RPM's.  This is the way my old "84" Porsche was connected, if the capallary tube isn't placed right you can get condenser freeze up. The older Porsches would freeze up if you asked for too much cold for too long


To get a better idea of what's going on with your A/C I would buy a cheap digital thermometer and place in the center vent.  You'll be able to watch the temps go up (compressor shuts down), then the compressor comes back on and the vent temps will go down.  It's a slow dance that you can watch.  


Also maybe the system is just low on Freon...  I would go to a local A/C shop and have them evacuate the system to be sure you don't have any leaks, then charge it.  I beleive your system will hold just a tad short of 2 lbs. of R34 freon.

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BTW, contributing members can access the climate control document here http://www.renntech.org/forums/files/file/1663-after-sales-training-climate-control-systems-diagnosis-repairpdf/


Creekman, what you described is used mostly on older cars but our cars (996s) use a variable displacement compressor as documented in the above doc.

Edited by Ahsai
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As Creekman suggests, I had mine checked for leaks (none found), emptied (as I was not sure what was used by a previous owner) and recharged early this summer with R134A at a VW dealer. Too easy and lots of cold air now! 

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