Expert: Roland Finston - 7/6/2011

Question
QUESTION: do i need to have the ac clutch running to check the freon level?

ANSWER: No it can be measured without it running.

---------- FOLLOW-UP ----------

QUESTION: does the the clutch need to be running when adding freon

Answer
Yes, to properly empty the can of refrigerant into the system the compressor clutch has to be engaged, and the compressor spinning.  At the clutch you will find a black wire (ground) and a dark blue/black wire (12V supply wire). Notice which wire is connected to which pin of the compressor clutch. Leave the normal plug disconnected from the clutch. Then jump two wires: one from the battery + terminal to the pin that was connected bo the dark blue/black wire, and jump another wire to the pin that was connected to black ground wire with its other end to a nearby metal surface of the engine. Then if you have the refrigerant can and its adapter connector attached to the refrigeratnt system port you can start the engine, puncture the refrigerant can, and the compressor should suck the refrigeratant out of the can. You can follow the progress by having a small scale nearby and watch the can get lighter as the refrigerant leaves it. Then shut the port, turn off the engine. Put the plug back on the compressor in place of the jumpers, and start the engine. If you have added enough refrigerant the clutch will close automatically. If not, then add another can of refrigerant. In mentioning the colors of the wire, I assume you  have a Chrysler product.
Roland