Update: Got another climate control unit from wreckers ($350), didn't fit, different plugs on the back, same number of pins but just slightly different so don't fit. I guess the S1 and S2 stageas are different there. Wrecker is going to try to find one from a S2, don't fancy my chances though. Might have to try Nissan, can't imagine what it would cost......
Had a look at the temp sensor (to the left of the steering column?), seems OK but I don't think that would be the problem seeing as the problem is the same in auto or manual mode?
Hmm, might have to live with it for a while.