Disconnect the wire connector on the clutch unit, this will disengage the clutch on the air con pump.
This will at least get the air con off, can't help with relay i'm a fraid but would be worth ringing FOCUS/MONDEOPART 01603 866999, as they dothese all day long.
I am a bit confused as aircon NOTHING to do with the temperature at all, you can have it on on HOT and it will be HOT, are you saying that it will not get HOT when HOT is selected on temp dial ?
If so could be a vacuum leak as the flaps are vac operated, and could be stuck in the cold position.
tabetha