My a/c system is cutting out intermittently. It will work fine for 10 minutes and then go completely dead in all settings. Then a while later it will start working again. Car is 1979 XJ6 SIII. I've read all the relevant threads here and studied the S-57 wiring diagrams. Before I start tearing the dash apart to look for loose connections I started by checking all 4 fuses. Now I am trying to see if the main relay is working correctly. Here is what I've done so far:

• Brown/white wire in the middle has 12v
• Black wire in lower middle right has good ground
• Jumping 12v to the Green/slate wire runs the fans
• Brown/white in lower right has 12v with key off as it should.
• All terminals are tight with no burn evidence or corrosion.

I know the resister pack adds resistance in 3 steps to control fan speed at the 3 terminals marked “resister pack” but I have not found any guidance as to testing them. So here is the question: any other checks I can do or should I move on to the mode selection switch? Thanks for your help.

 

Well, I'm a little further down the road. After a lot of testing, studying wiring diagrams and talking to Gary at Jag-Aire I figured out the problem is my mode control switch. I made a little video that I hope will help someone in the future. Here is the