Project E36 M3 - Replacing the HVAC Blower Fan April 26 2024

Our Heating, Ventilation and Air Conditioning (HVAC) fan had been squeaking at certain fan speeds. It had a bad bearing and it was time to replace it. While we had the cylinder head off for a head gasket replacement, we decided it would be a good time to replace the HVAC fan, since access would be easier. This job was relatively involved and required us to create some custom tools to make the job possible.

There was no procedure for this job in any of our shop manuals, so we turned to the BMW community on the internet. There are several videos on this topic, but they all omit how the new fan actually goes back into its spot. The problem is that the opening in the firewall is 4.90 inches tall while the fan cages are 5.55 inches in diameter.

If you forced the fan through the opening, the fan would have to flex 0.65 inches, which would almost certainly break the cage. There was also no way to move the fan laterally enough to somehow maneuver it out of the way, as the fan housing gets in the way. One person was honest enough to admit that they had to bend some of the firewall sheet metal out of the way, install the fan, and then bend the sheet metal back. That is one way to do it, but there is no way we are going to do that to our beloved M3.

There are some fan assemblies out there with removable fan cages, but these were not available at the time of writing.

Before we begin, we will need to close a couple of flaps in the HVAC system to allow for disassembly. Start by turning the key in the ignition to position 2. This is the position where the car has power for the HVAC can run, but does not crank the engine. Turn on the fan and then turn on the air recirculation. The recirculation command closes a flap in the system that we need closed for this job. While the recirculation is still on, disconnect the battery so that the flap stays in the closed position.

To access the fan assembly, we will have to remove several parts, the first being the plastic windshield cowl at the base of the windshield. To remove the windshield cowl, there are a few plastic nuts to remove. Three are circled, and there are more nuts on the other side. We will also need to remove the windshield wiper arms to remove the windshield cowl. You may elect to mark the position of where the windshield wipers touch the windshield to aid orientation during reinstallation. We used blue masking tape for this.

To remove the windshield wiper arms, pry off the black caps with a flathead screwdriver. Undo the 13mm nuts with a socket. With the nuts removed, use a windshield wiper arm removal tool to pull the windshield wiper arm off the stud. 

There is a bolt on each of the hood hinges that allow the hinge to get out of the way to completely remove the windshield cowl, but this is optional. The cowl can remain in place and be pushed out of the way as necessary. 

Remove the ECU cover to allow the harness more room to get out of the way. There is a rubbery sound insulation piece you have to remove first. It is held in by several plastic rivets. Pry out the mushroom-like piece in the center, and the rivet will release its grip. Be very gentle with the sound insulation piece, as it will crumble and crack with even slight bending. If you want to replace this part, it is BMW part number 51481977110.

Next, the plastic ECU cover can be removed by removing the philips head screws. This will allow the harness more freedom of movement and grant us better access.

Next, we want to free up the wiring harness box so we can move it out of the way. There is one bolt on each side holding it on.

Remove the firewall panel. There are five screws that hold it in place. The fasteners are different, so take note of which ones belong where.

Remove the HVAC fan cover by prying up the 3 metal clips and loosening the plastic bolt in the center. These are easy to lose, so we recommend pliers. The plastic bolt in the center is a quarter-turn fastener.

Consistent with automotive conventions, we will refer to right-hand-side (RHS) and left-hand-side (LHS) descriptors from to the perspective of someone sitting in the driver's seat.

Remove the LHS HVAC duct assembly. Start by removing the two metal clips by prying them out with a flathead screwdriver (not shown).

Next, unhook the cable linkage by squeezing the plastic stud together with needle nose pliers and working the cable end off the stud.

Remove the LHS HVAC duct assembly. 

Remove the windshield wiper linkage and motor. At the base of the stems, are large nuts. Use a 27mm socket or wrench to remove the nut.

There are a few additional fasteners holding the wiper assembly to the chassis (not all shown). Undo these fasteners. Once the wiper linkage is loose, drop the linkage into the chassis, point the wiper arm stems towards the front of the car and then maneuver the linkage out.

Remove the 2 wires from the HVAC fan motor. They simply slide out of their connections. Clip the zip tie holding the harness in place. Remove the clip holding the fan motor by pulling forward and up on the bottom tab with a pick. The fan assembly should be loose now.

Now comes the part that really stumped us. There is no way we could find to maneuver the fan assembly out of its location. Our solution was to cut out the RHS fan cage. We used a pair of diagonal cutters to snip the spokes of the fan cage. This allowed us to angle and maneuver the fan cage out. With the RHS cage removed, it is possible to move the rest of the fan assembly to the LHS and then out through the space where we removed the windshield wiper.

As you can imagine, if it is impossible to remove the blower fan assembly in one piece, it is impossible to reinstall the blower fan assembly in one piece. To install the new fan, we had to remove the RHS cage from the fan assembly, maneuver the parts individually into their final positions and then reassemble the parts in situ. 

IMPORTANT: before removing the RHS fan cage, mark the clocking of the fan cages relative to each other. They are balanced as an assembly and need to be clocked in the same orientation. We used tape, but would recommend a paint pen instead, because the tape can be tricky to remove after the fan has been installed. Just mark a fan blade on each fan cage that is in line with the other side.

According to internet citizens, at some point in time there were blower fan assemblies with detachable fan cages. This would certainly make installation much easier. However, we weren't able to find a fan with removable cages. At the moment they are not available. Nonetheless, we bought a Mahle fan with cages described as non-removable and tried to remove the fan cage. We couldn't get a pry tool into place because of the geometry. We also tried using a long punch to tap the fan cage off the shaft, but that didn't work for us either. We tried using some 3-jaw pullers, but the jaws were way too big to fit between the spokes. The spokes of the fan cages are skinny and plastic, and being too forceful is an easy way to break them.

We had to resort to building a custom 4-jaw puller tool. The arms are skinny enough to get where they need to go, and the arms are spaced out to work with the weird 13-spoke arrangement of the fan cage. After going through this ordeal, we decided to make this tool available to make the job possible for others. You can get one here: E36 blower fan tool set.

IMPORTANT: Make sure you are removing the correct fan cage. It should be the RHS fan cage that is removed.

The Mahle fan cage was press-fit onto the motor shaft, so we simply used our 4-jaw puller tool to pull the fan cage off the motor shaft, but we can make no guarantees that all fans will be like that. If your fan cage is staked to, molded to, or otherwise permanently attached to the motor shaft, this won't work.

We first tried to use commonly available tools to install the fan cage in situ. We tried hammering techniques, but there was not enough space to swing the hammer. We tried hammering on a long socket extension to allow us the room to swing a hammer, but the off-centered angle of the extension made it ineffective. We tried c-clamps and trigger clamps, but none of them could fit into the tight space. We tried using our brute strength, but it was not enough.

We finally gave up and developed a tool. Prior to reassembly in situ, we found it helpful to mock up the fan and tool assembly on the bench first. This allowed us to mark which spokes the bolts would travel between in order to get the fan clocking in the orientation we need. We used a paint pen to mark the spokes that the installation tool bolts should travel between.

With the RHS cage separated from the fan assembly, the RHS cage can be placed in position, followed by the rest of the fan assembly.

IMPORTANT: double check the orientation of the RHS fan cage, because it is possible to put it on the wrong way. Once the fan cage is installed, cutting it out is the only way we know of to get it off.

Align the two fan cages in their balanced orientation, referencing the marks you previously made. Position the installation tool. One end of the installation tool has a tether so that it can be retrieved in the event that it falls into the HVAC ducting. Tie off the tether to something. The installation tool will be loose at first. Tighten the bolts until the slack is taken up and stop to check that everything is lined up and in proper alignment. Alternate tightening each bolt a turn or two at a time so that the cage gets pressed on straight. Remove the tool after the fan cage is installed.

Reattach the clip that holds the fan motor in place. Plug in the electrical connectors and zip tie the harness to the clip. The electrical connectors are gendered such that you can't mix them up.

Once the new fan and LHS duct is installed, and we recommend function testing the fan before buttoning everything back up. Reconnect the battery, and turn the key in the ignition to position 2. Turn on the fan and make sure there are no weird noises. Check that the fans can turn freely and aren't rubbing on the plastic housings, wiring or anything else. We had to adjust our LHS fan cage slightly inboard by putting a socket and long extension on the center of the fan cage and tapping it in a little with a hammer. We also had to adjust our wire routing to avoid rubbing the fan cage.

Assembly is the reverse of disassembly.

This is still a difficult job, with many steps and tight spaces to work in, but without the custom tools we made, we don't know how this job is possible. If you can do this job without the special tool, you have our admiration, but if you get stuck, we are here to help. With our new blower fan assembly in, the fan no longer squeals when running.