A/C Clutch will not activate.

I've gone through what I thought was a logical, systematic troubleshooting technique and I struck out. First, I ran 12 volts to the clutch with a jumper and the clutch activated as it should. I need the clutch to run so I can add some charge and look for leaks. So, I next trouble shot the relays controlling the system. I removed the relay covers and cleaned the contacts with emory paper, put 12 volts across the coil and the relay activated as it should. There are 2 relays affecting the A/C control so I went through the same exercise with both and still no power to the clutch. The fan blower switch controls the fans asI would expect and the wire colors have nothing in common with the clutch so I gave little attention to the fan switch.. The only stone left unturned is the dash switch which selects off, defrost or cold. I find the access is very difficult and though I'v removed the radio and various other dash components I find myself not wanting to go there.
Any words of wisdom from the wise men visiting the forum would be greatly appreciated. I've only got so much hair left and I'd just as soon not donate it to the Stag A/C.
Thanks in advance , BIG TIME,
Mark

Well, do the condenser fans run? According to my schematic, they get fed from the same circuit as the clutch, so if they are running, the problem is between there and the clutch. I see the "high head" switch between them, so that's the next place I would go.

If the fans don't run either, check whether the warning lamp for the rear screen defogger will come on with the A/C switched off (and ignition on of course). If not, the fuse may not be passing enough current. Do a voltmeter check right at the fuse. If you don't find 12v on either side of the fuse, the problem is likely to be between there and the ignition controlled relay.

If the light does come on, then turn on the AC and see if it goes off. If so, the AC control logic is working, and the problem is likely to be either the AC relay or the wiring from it to the condenser fans.

That should be enough to get you moving forward. One other note, with these higher power circuits, it is very easy to get fooled by readings of continuity. In my opinion it is better to test things in-circuit (meaning check the voltage while they are trying to power whatever) than try to check continuity with things disconnected.

-- Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
71 Stag LE2013LBW awaiting (manual + J type) gearbox rebuild

Thanks Randall,

I will start with the condenser fans. The PO added a manual toggle switch to turn the fans on, on demand. I note the thermo switch in the radiator end tank is not being used and do not know how it was wired originally.

To keep things interesting my faux leather Stag operations manual is missing the diagram for Left hand drive A/C cars but does include the legend. The number of items listed is 110 and all other schematics for right hand drive top out just over 100. So, I' missing part of the picture, wouldn't you know it!

I will follow your recommendations searching the function of the rear screen defroster circuit, make direct measurements of voltage across fuses that pass continuity testing and spend some more time with the relays. The relays don't have a diagram on them as is usual and I need to recheck what I was looking at. I know 12 volts across the coil energizes the relay but I'm not sure I'm getting 12 volts from the "switched" terminals.

Right at bed time it came to me that I should run a continuity test from the high pressure switch to the relay. I'll have to figure out which terminal is supposed to be sending the 12 volts that direction with lack of diagrams and so on.

I'll share what I find with you and the forum. I've found TriumphStag.net to be a most valuable source of information along with a few friends.

BTW we call this my wife's car and it will be published in Hemmings Sports and Exotic Car November issue. So, you know the A/C has got to be working.

Thanks again,
Mark