What outputs does the standard heater control have for AC?

[dnb]

Is there anything other than an on/off signal that activates the clutch on the compressor?
Presumably there are some sensors to monitor as well?

I know the engine ECU is supposed to have an output to disable the AC under certain conditions, but not sure what these are, other than when the engine is near full load and all the power ought to be doing sensible things like driving the wheels.

I have the prototype version of my new control box (with closed loop control features) sat on the bench, but I don't know how the TVR AC bits of the controls work since I never had AC on my car. It would be nice to have one design that can do both - then I can think about an electric motor driven compressor (I am having electric PAS in the future, so why not electric AC? )

[The AJP Griff]

When you press the button to turn on the a/c,12v will go from the heater control unit,down to the trinary switch.At this point,if the gas pressure is ok,the 12v will then go back to the compressor relay.There is also a temp switch near the evaporator which will cut out the circuit if the evaporator gets too cold,ie ice.The relay for the compressor normally has a switched earth provided from the Lucas ecu,which is simply provided whenever the ecu is running the engine.One other temp switch is the one on the compressor,which cuts out if it gets too hot.I think that about covers it,if you need a chat,Dave,give me a call on the mobile

[dnb]

Thanks Mike. I hope I'll catch up with you at some point over the weekend.

[Uncle Fester]

David, any idea when these will be available? I want one.
Not 100% if it applies to all years, or just the earlier A/C cars, but the printed circuit board behind the heater control required modification because it hadn't been originally designed to switch the A/C.