Hi all,
I've had an intermittent fault with the fan which provides fresh air to the cabin. Sometimes it would work other times it wouldn't. A couple of weeks ago it finally stopped working and wouldn't come on at all at any speed.
I removed the fan from the heater box. to do this, disconnect the brown connector on the side of the fan casing towards the front of the car with the 4 wires going into it. Next disconnect the single black connector with a green wire going into it at one end and a black wire coming out the other end. Next, unscrew the 3 screws holding the fan unit into the heater box. The fan should drop out into your hands.
With the fan assembly on the bench remove the remainder of the wiring. The large black and red cables and connectors should just pull off. However, if they have overheated they may need persuading with a screwdriver to lever them off. The other end of the cables pas through a hole in the plastic housing via a rubber concertina seal. Pull back the seal to reveal a clip holding the plug in place. Insert a small flat bladed screwdriver between the clip and the plug and pull gently on the plug. It will release and you should be left with the wiring in your hand.
Locate the three rectangular holes in the plastic housing just below the circular rim at the base of the fan impeller. These are the 3 locations where the rubber fan mounts just 'clip' into the plastic holder. Inset a flat bladed screwdriver into each hole in turn and push on the rubber at the same time as levering it such that the rubber is pushed out of the casing towards the fan impeller. Work around all three moving them a bit at a time. Finally the fan and impeller should come out of the housing.
Screwed to the plastic housing is the speed control module. It consists of two Motorola T1829-1 Transisitors mounted on a small printed circuit board. Reading about this problem on other forums it would seem that the transistors are favourites for blowing. However, in my case the transistors checked out OK. My problem was evident from the high temperature marks on the spades where the external cables join onto the PCB via the connectors. I cleaned up the spades with emery cloth and squeezed the connectors with a pair of pliers. This increases the surface area in contact and the contact pressure which both reduce the resistance. If there's no resistance there won't be any heat produced.
I checked the brushes on the motor whilst I had the motor out in my hand but they were fine. I greased the 3 rubber mountings to make it easier for the fan motor to slip into the plastic housing easier. I rebuilt the fan assembly and fitted it back into the car.
I now have a working heater fan again at all speeds.
Hope this helps someone else with a similar problem.
Cheers
noz