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Full Version Heater Fan Intermittent Fault

Club XM Forum > XM General Issues
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.


noz cool.gif
Well done Noz. I have had three of these motors fail and in every case it has been the transistors, as they are originally rivited in they have to be drilled out but can be nut and bolted back in. I wouldnt know where to obtain the original transistors but any high current PNP TO3 type will do, if anyone needs them I can let you have a type No and details of supplier. Have not come across your problem Noz, well at least not on the heater, but have on other electrical components.


When do you get the time to drive this car ??

it seems you are always under the bonnet or under the car!

Mine hardly ever needs anything doing at it !

Must of been a bad one you got hold of m8 ??

Or is it mine thats been well looked after with over 200,000 mile on the clock ??

Good bit of info to know

ttfn m8

You're not far off the mark there.

However, would it be as much fun if nothing ever went wrong? You'd be better off driving a Japanese car !


noz cool.gif
I had a similar fault with the heater fan but after removing the fan, relay panel, glove box (I think there is a fan relay behind the glove box) and part of the facia (to get at the control) I found it was the fuse under the bonnet. It hadn't blown but had overheated and went intermittent. Always look for the simple things first!

It seems that the higher the mileage the more reliable they are! out of four that I have had, the most reliable one I bought at 244k and sold at 292k, hardly a thing went wrong.

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