No heating, just blower and a/c. Mondeo Mk2 w/ SATC?

The car is a 2000(W) with the semi-auto climate control. It doesn't matter if air-con is on auto at a set temp, manual or just off, no warm/hot air comes through on any setting. It just blows air, or ice cold air if I put the air-con on LO.

Also when the blower or air-con is on the engine fan cuts in after a short period, which has never happened before.

I took it to a garage and they said it could be the solenoid or the switch pack (front display unit.)

With regards to the latter, is it just the SATC display unit I'd need, or would I need the wiring loom, sensors, etc to replace with it too?

Any other ideas?