E30 Zone

hi guys have a dilemma,
got in the car this morning turned the heaters on and they were blowing fine also tried the air con and it was blowing ice cold,all good.
took it over to my bmw specialist to have an inspection 1 service and then driving home the heaters dont work and the electronic unit is buzzing even when the engine is off?can anyone shed some light please as im planning to put it up for sale soon and want it to be good for the new owner.
any help/solution appreciated cheers

the common faults I know of are a capacitor on the circuit board inside the climate control unit failing which only costs about 40p to replace and the other is the hedgehog resistor under the dash.
my symptoms were, heaters switching on and off randomly and the inability to use the unit when the lights went dim and all sorts of weird and horrible noises, buzzing and sometimes the unit running even with the ignition off.

now all the above was fixed by replacing my climate control unit (my car is a '96 and the replacement came from a '99 car costing me £6 from the scrappies) for a working one so I must have had the capacitor fault

HTH mate