[mycastle]

Going through my A/C on a 78 911 SC - Euro. It may not be a factory install because the "front" condensor is in the back behind the driver side rear wheel.

I am trying to figure out if the compressor clutch is functional.

Here is what I have right now.

System not run since I got it in 2009. Have not hooked up the A/C belt since motor installation. I checked for pressure by pushing in on one of the fill fittings and it still has pressure (so maybe just needs a recharge).

According to the schematic from the bentley (dwg 970-12):
Ignition in run should pick up the A/C relay (have not found it yet - not in the fuse box as it should be - another indication that it was not a factory install).

Turn the A/C fan switch to postions 1, 2, or 3 - Evaporator fan blows with increasing speed. This tells me that A/C relay (where ever it is) is working.

That should put power to the A/C switch which should pick up the clutch - got nothing.

Either switch or clutch is suspect at this point.

Placed twelve volts onto the wire leading to the compressor (down stream of the temperature switch - heard a relay pick up and then the condensor fan started. Did not hear anything at the compressor; spun the pulley and it moved freely. This gives me an indication that the A/C temperature switch may not be functioning, but I am not sure if it tells me the compressor clutch is not functioning.

Did some resistance checks and found the following:
from the power line to compressor case - 3.4 ohms - looked reasonable for a coil.
Compressor case to ground - 90 ohms - Shouldn't the case be a solid ground? Thought I would ask before I make it a solid ground and then fry something in the process!

Thoughts?