Marea 1.8 elx 16v

heater (and aircon) only seem to want to work when the engine temp gets high (half way up the gauge), but even this is very intermittent.

Tried moving wires etc about (both when fan working and when not) as i thought it could be a loose connection, but no joy.

Turn engine off, it cools down, fan won't work.

Any thoughts pleeeeze.