Heater Blower Working Only on Max
In this wiki we will be looking at troublesome heater blowers. This is what helps keep you warm in the winter and if you’re posh and have aircon, keeps you cool in the summer. The most common issue these seems to suffer with is that the blower stops working on positions 1, 2 & 3 but work fine on 4 (full power).
Contents
Overview
There is usually one of two possible faults that would cause these symptoms; the first being the actually blower motor being worn out or seized up, and the second being a failed resistor pack. The motor's job is pretty obvious; it spins at a variable speed which the user controls from the comfort of their seat using the switch on the dashboard. The resistor is what actually controls the amount of voltage going to the motor depending on the switch position, where the lower the desired speed is set on the switch the more resistance is applied meaning less power gets to the motor and therefore is spins slower.
Resistor
Firstly, we’ll go through the most likely failure, the resistor pack. Luckily this also happens to be the cheapest and easiest as well, but that's not always the case!
Now depending on whether you have aircon or not will affect where your resistor is and which one it is. For non aircon cars it is on the left hand side of the airbox and is removed from inside the car.
First open up your glovebox and then unclip the two straps so that it drops down into the footwell.
Then you need to remove the trim panels, the first one to come out is the upper panel which is held in by a couple of screws near the latch and a clip further underneath. Then the side panel needs to come out, this is held in by a single screw at the front and then a couple of twist clips (I did manage to change a resistor by just removing the side panel but refitting the panel was more hassle than it was worth with the upper still in place)
Now we can see and access the resistor, if you stick your head under the dash looking up you should be able to see the brown top of the resistor with a single 4 pin plug connected. Simply pull the plug out and then the resistor which is held in by two plastic tabs. You have to do this by touch and one handed but it’s pretty simple to pop out once you’ve got a feel of the tabs.
As any good workshop manual would say, fitting is the reversal of removal. You might want to test the fans before you put it all back in though.
Blower Motor
If a resistor swap fails to solve the problem then it’s time to move onto the motor. This is accessed from the engine bay by removing the bulkhead panel. Again a pretty simple task but I’d suggest having some small zips ties to hand, all will become clear.
The panel is simply held in place by 4 7mm hex screws, however there’s a few things attached to it which need removing first, all dependant on the model as well. In this example the car is a 325i. First off you’ll need to lift up the bonnet seal as this slides over the top of the panel. Then you’ll need to undo the 2 screws holding the C101 plug to the panel and the 2 10mm plastic nuts holding the wiring tray in place. The throttle cable then tends to be cable tied to the plastic clips so simple snip these and the panel will come away easily once the 4 hex screws are undone.
Now you can see the top of the airbox, the motor is lurking under the plastic trim pieces, with a fiddle these just pop off, outers seem to come off first. With those out the way the motor is exposed, there are two wires connected to it which just pull off their terminals and then a single metal clip holding it in place. You’ll need something like a screwdriver to pop the clip as it’ a pretty tight fit, with that undone the motor will just lift out.
With the motor out you’ll be able to get a good idea of its condition. Give it a spin and see how free It feels. It may have started to seize up so a good soaking in something like WD40 may loosen it up and give it a new lease of life.
