1996 1997 1998 1999 BMW E36 3-Series M3 Climate Control HVAC Repair Instructions

Introduction

With over 10 years experience repairing this device, we can confidently assure you that the process outlined will resolve the failure of this climate control device. Please follow instructions carefully and take precaution when necessary.

 

The body electronics of an E36 BMW 3-Series (318, 320, 323, 328, M3) are generally reliable but the HVAC controller’s internal power capacitor commonly results in the unit’s premature failure. When this problem occurs the end result is no heat or air conditioning.

Because this is a manufacturer defect, purchasing a new unit from BMW for $600+ may allow this problem to arise again in the future. This DIY outlines the process required to conduct a component-level repair of the automatic HVAC controller of an E36 BMW to address this problem.

 

Troubleshooting

The most obvious symptom of a failing HVAC controller is the intermittent operation of the unit. This condition is easily noticed when:

1. The controller's LED backlit display flickers on and off randomly
2. Heat blows from vents at highest speed
3. One or more LEDs may be illuminated but none of the buttons work
4. The blower motor may not run consistently or at all
5. The air conditioning does not work. Compressor does not turn on.
6. The auxiliary cooling fan runs inappropriately (like when the A/C is off and the engine is cold in wintertime)

Prerequisites

Tools

• T7 Torx Driver
• Small slotted screwdriver (slot < 1/4"), or an equivalently-sized dowel about 2" long and a hammer
• Soldering iron (25-50 watt range with fine point tip)
• 60/40 Tin/Lead Rosin Core Solder, 0.31" diameter (Kester "44" or equivalent)
• Desoldering bulb OR manual pump OR station
• [Optional] Small workbench vice with "soft jaws" (foam padded)

Parts

• 0.47µF 50V Radial Capacitor (supplied)

[Optional] Temperature sensor fan (BMW Part # 67-32-8-378-663)

[Optional] Final Stage Resistor (blower motor resistor) BMW Part # 64.11 6 929 540

Removal / Disassembly Procedure

1. Disconnect the negative battery cable from the battery terminal. A short 13mm socket and ratchet will be required. Insulate the terminal in a work glove or otherwise wrap it such that it will not contact either the battery terminal or any nearby metal including the vehicle body.
2. Move the gear selector for clearance purposes. Apply the parking brake to ensure the vehicle will not roll, press and hold the brake pedal for good measure and then move the gear selector away from the dashboard so the OBC can be removed without hitting the selector. In manual transmission equipped vehicles this will likely be as easy as moving the selector into neutral. In automatic transmissions equipped vehicles, however, it is necessary to turn the key to position 1 (in addition to stepping on the brake pedal) to disable the interlock before the selector will move aft.
3. Remove the OBC. Turn the palm of your dominant hand face up and touch the roof of the pocket just below the OBC to find a hole. Put your finger in the hole and press directly upward to reveal the OBC's spring-loaded plastic locking tab. The tab won't depress much but it must be fully depressed to release the OBC. While pressing the tab upward, simultaneously pull the tab (and thus the OBC) toward you until the unit begins to move forward and is thus unlocked. Once the OBC is unlocked, put your finger behind the OBC and pull the unit toward you to remove it from the dashboard. The OBC may remain attached to the vehicle.
4. Return the vehicle to first gear or Park, as appropriate to prevent the vehicle from rolling and remove the key from the ignition if appropriate.
5. Remove the HVAC Controller. Reach into the hole in the dash left by the OBC and push on the back of the controller to push it forward and out of the dashboard. This will expose two cables that must be disconnected. The first cable is a large bundle of wires terminated with a large blue connector. To remove the connector, slide the white locking lever down and away from the cable end so that it mates with the case of the controller. The second cable is a simple multi-conductor cable. Firmly grasp the connector and pull it from the socket on the controller. Do NOT pull either connector by the wires.
6. Prepare a workspace suitable for electronics rework including ESD protection. Make sure your workspace has bright lighting, a magnifying lens, soldering and desoldering equipment, and most importantly, an effective means to prevent electrostatic discharge (ESD). This should, at a minimum, consist of a properly grounded wrist strap and an anti-static mat. If you attempt to do this repair in the winter or at any time the relative humidity is lower than about 60%, a very real risk of ESD exists. If ESD occurs while holding either circuit board permanent damage to the controller electronics may occur. For reference, I conducted this repair in December with an indoor relative humidity of 45% and I noticed several ESD events while I was preparing the workspace. Don't think ESD won't happen to you, because by the time you notice it, the damage is already done.
7. Remove the temperature sensor fan. The fan must be removed before disassembling the unit, but it need not be replaced unless the fan does not spin freely. It is replaceable from BMW, but compressed air and lubrication will make it run more efficient and quietly.
8. Remove the controller faceplate. Place the controller on its face and remove (4) T7 torx screws holding the chassis to the faceplate. Then pull to detach from housing.
9. Detach the front logic board from the case. Push the front logic board (the one with the display) up slightly and then pull the bottom of the board (near the two ribbon cables) out from the case. Once the front logic board is removed, it will fold away from the case but will remain attached to the inner logic board via two ribbon cables. Be very careful not to stretch those cables and protect glass LCD from falling onto a hard surface.
10. Remove the rear logic board from the case carefully.

 

1. Desolder the existing capacitor. Add ample fresh solder to the contact points, then use desoldering braid or a desoldering gun to absorb or suck the solder out of the holes. Gently pull capacitor out Without damaging contact points! This is important. Be careful!
2. Install the new capacitor. Because this capacitor is radial instead of tantalum, the pins can insert in either direction.

Installation / Reassembly Procedure

1. Clean the case and logic boards of dust. Using a can of compressed air, thoroughly clean both logic boards, the temperature sensor fan, and fan duct of any dust.
2. Insert the rear logic board into the slot in the case. Correctly orient and install the temperature sensor fan duct through the hole in the logic board and then carefully insert the logic board into the slot in the case. Push it until you hear the locking tabs in the board snap into the holes on the side of the case.
3. Install the temperature sensor fan. Note that if you chose to replace the fan, the new part will come with two screws and some plastic spacers. The screws are similar to the originals but about 2mm longer to accommodate the spacers. Don't mix them up. Make sure the yellow fan connector is fully seated in the red socket on the controller.
4. Attach the front logic board to the case. Insert one end and then push the other end in to secure it.
5. Install the faceplate. First snap it back into place and then install the four screws to secure it.
6. Install the controller in the vehicle. Attach both cables, engage the white connector lock and then simply (but carefully) press the controller back into its slot in the dashboard.
7. Install the OBC. This is another press-fit.
8. Attach the negative battery cable to the battery terminal.
9. Turn the ignition key to position two to test controller functionality.

 

Links:

New Repair Capacitor:

www.ebay.com/itm/391346397561

Fast Professional Repair Service:

www.ebay.com/itm/391232582641

 

 

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