BimmerFest BMW Forum banner
1 - 3 of 3 Posts

Rambling Wreck
2,073 Posts
Discussion Starter · #1 · (Edited)
By now, we're probably all familiar with the infamous BMW HVAC system stink. There's just something about the design of the BMW heater box - the large, complex black plastic enclosure that sits between the dashboard and the firewall and contains the HVAC blower, A/C evaporator and heater core - that allows moisture to build up and provide an inviting environment for mold and bacteria to grow. Even though I've been pretty conscientious about turning off the A/C and running fresh outside air through the system before reaching my destination, some recent rainy weather has helped the smelly stuff to take hold.

With two cans of Einszett (1Z) Klima-Cleaner on the workbench, I cleaned my car's A/C evaporator twice in the past week. Here's a comparison of the two different methods I used. If you're thinking about cleaning your car's evaporator, I hope this article will provide you with enough information to decide which way you want to go.

First of all,

Disclaimer & Safety Tips

  • DISCLAIMER: I AM NOT A BMW TECHNICIAN. I am sharing my experiences from cleaning the A/C evaporator on my E46 sedan with automatic climate control. Depending on the year and configuration of your vehicle, your car's HVAC system may vary. I will not be responsible for any damage or injury that results from following anything I have posted in this thread. Verify part numbers before you purchase your own materials. It is your responsibility to also verify technical information with a trusted source, such as BMW TIS, your copy of the Bentley Publishers repair manual, or a reputable mechanic. If you are not comfortable with doing this work on your own car, I recommend that you seek the assistance of an experienced friend or your mechanic.
  • If you or your passengers have sensitivities to mold, dust, bacteria or the chemicals used in A/C treatments, choose your cleaning product with care, and consider having a professional do the work.
  • Although I used 1Z Klima-Cleaner, you may prefer to use a different product; whatever you choose, make sure it is designed and labeled by its manufacturer for use in automotive HVAC systems. Use appropriate safety measures, have proper ventilation, and don't smoke when working with chemicals, especially aerosols. Follow the cleaning chemical manufacturer's instructions completely. Keep kids and pets away from the cleaning products and the residues that flow out of the heater box drain. Safely dispose of cleaning residues in accordance with the manufacturer's instructions.
As always, you're welcome to do things differently and discuss your method here.

Before Starting

I parked the car on a level surface to facilitate drainage from the heater box.

I was fairly certain that my car's heater box drain wasn't clogged, but before you start taking anything apart, I strongly recommend that you check the heater box drain. With the car parked in a well-ventilated area and the engine running, let the A/C run for several minutes. Wait for condensate from the heater box to drip onto the pavement or into your collection pan. If water drips readily, then your heater box drain isn't clogged, and you can proceed with the cleaning. However, if no water comes out, then the heater box drain is probably clogged, and you should not proceed with cleaning until the drain can be cleared. If the drain is clogged, the liquid residues from the cleaning process will have nowhere to go, and they'll just accumulate inside the heater box and encourage more funky stuff to grow inside.

After things have been taken apart and the evaporator is exposed, there will be another chance to re-check the heater box drain. See "The Cleaning Process" below.

Method 1: Spray Into the Final Stage Unit Opening from the Passenger Footwell

Materials for Method 1
  • A/C evaporator cleaner, including spray hose attachment
  • Aluminum foil turkey pan
  • Towels
Tools for Method 1
  • Common sense
  • Patience
  • Eye protection
  • Disposable rubber gloves
  • Knee cushion
  • Plastic interior trim removal tool set
  • Torx driver set
  • Screwdriver set
  • On-board monitor removal tool set (if the car has a factory navigation system). For widescreen monitors, the BMW part number for the tool set is 83 30 0 493 961.
  • Spray bottle filled with clean water
Basic Procedure for Method 1
1A. Remove HVAC controls (for cars without navigation) or on-board monitor (for cars with navigation).
1B. Reach into HVAC control/on-board monitor cavity and unclip top tab of passenger footwell duct from heater box.
1C. Remove glovebox and plastic footwell panel at bottom of glovebox.
1D. Wiggle passenger footwell duct out to reveal air distribution motor.
1E. Remove air distribution motor in front of final stage unit.
1F. Remove final stage unit. Line the area beneath the final stage unit opening with towels.
1G. Clean the evaporator. See "The Cleaning Process" below.
1H. Assembly is the reverse of removal.
1I. Start the car and run the HVAC system for several minutes, at maximum blower speed, to dry it out.

Observations on Method 1
  • The final stage unit opening isn't very large, so my view of the evaporator surface was limited. I moved the end of the hose back and forth and up and down inside the box. It took some patience to get good coverage.
  • There's a plastic shroud above the final stage unit that makes spraying the passenger side of the evaporator difficult. See Photo 2, which I took with the help of an inspection mirror. Snaking the spray hose between the shroud and the evaporator is possible, but it raises the risk of bending fins on the evaporator surface.
  • As many have observed when replacing the final stage unit, it's a cramped space in which to work, and I had to lie in the footwell on one side to get a good view of the evaporator and guide the hose into the opening.
  • As of the date of this post, the removal tool set for the on-board monitor is still available through BMW dealer parts departments. The list price for the set is about $12. Please note that the tools pictured in Photo 1 are only for the widescreen monitor, not the earlier monitors with smaller screens. The tools aren't absolutely necessary (search this forum for "steak knife" ), but they're very helpful.
  • It's a slightly less dirty job to work in the interior than it is to work in the engine bay.

Method 2: Spray Into the Blower Housing from the Engine Bay

Materials for Method 2
  • A/C evaporator cleaner, including spray hose attachment
  • Aluminum foil turkey pan
  • Towels
Tools for Method 2
  • Common sense
  • Patience
  • Eye protection
  • Disposable rubber gloves
  • Torx driver set (magnetic drivers are a must)
  • Screwdriver set
  • Metric socket set
  • Ratchet and extensions
  • String, stiff wire or hook tool
  • Painter's tape
  • Duct tape or gaffer tape
  • Spray bottle filled with clean water
Basic Procedure for Method 2
2A. Disconnect battery.
2B. Remove microfilter, microfilter air plenum, heater bulkhead, heater bulkhead rubber gasket, strut brace (if present), and top engine covers. Replace strut brace (if present) after removing engine covers.
2C. Remove passenger side air flap from blower housing.
2D. Remove outer blower cover and passenger side blower cover.
2E. Unplug blower wire harness. Unclip blower retaining strap. Lift blower off of motor cradle, and pull complete blower out through the passenger side of the opening above ignition coils.
2F. Cover fan electrical connection with painter's tape. Place a towel on top of the back of the engine.
2G. Clean the evaporator. See "The Cleaning Process" below.
2H. Assembly is the reverse of removal.
2I. Start the car and run the HVAC system for several minutes, at maximum blower speed, to dry it out.

Observations on Method 2
  • To me, this method gives the best, most direct access to the evaporator surface. See Photo 3, which I took shortly after spraying the last of the foam onto the evaporator.
  • It's better to use this method when the engine is cold, since all of the work takes place at the firewall.
  • I disconnected the battery because an E46 Fanatics member reported causing sparks when the metal blower strap made contact with the chassis.
  • I reattached the strut brace after removing the engine covers. The brace made a good handhold and a place to rest my elbows.
  • The spring clips that hold the bottom of the outer blower cover are captive. Those four little Torx screws holding the outer cover and side cover would have been easy to lose without the help of magnetic drivers.
  • There was no need to remove the air flap on the driver's side of the blower housing since I could feed the blower out through the passenger side. If you've ever pulled the blower from an E36, the amount of space available to pull the E46 blower will seem luxurious by comparison.
  • I used a piece of string to pull and unclip the blower retaining strap. The strap fell out of the motor cradle as soon as the blower motor was free. I should have grabbed it before it came loose and fell against the evaporator.
  • Removing the blower exposed two rectangular holes in the motor cradle that allowed me to spray the upper portions of the evaporator, which are concealed behind the plastic blower housing.
  • I was careful not to flood the area around the final stage unit with the cleaner. The liquid could have seeped out of the heater box around the final stage unit. Short bursts were the key.
  • After emptying the can of Klima-Cleaner onto the evaporator, I wiped down the interior surfaces of the blower housing (including the blower outer cover) with a clean, damp towel. I also wiped up any cleaning liquid that was present on the motor cradle.
  • The blower retaining strap didn't want to hang in place from the motor cradle while I slid the blower back into the housing and onto its cradle. So I hooked the strap to the motor cradle, then taped it to the roof of the firewall cavity to keep it from falling out while I reinstalled the blower.
  • Compared to Method 1, this method required more time to reassemble everything, reconnect the battery, and start the car. I couldn't reconnect the battery without first strapping the blower into its cradle and reconnecting the motor wire harness, and I wanted to run the system with the microfilter in place to avoid introducing dusty, unfiltered air into the heater box.

The Cleaning Process

This procedure applies to both Method 1 and Method 2.

I placed the turkey pan underneath the car, roughly below the HVAC controls, and sprayed several spritzes of clean water into the heater box in front of the evaporator. I waited for the water to run out of the heater box and drip into the pan, then adjusted the placement of the pan as needed.

I shook the can of 1Z Klima-Cleaner per the instructions, then attached the supplied spray hose and started spraying the surface of the evaporator. I didn't unload the entire can into the heater box in a single spray; the foam expands pretty quickly, which means it can easily get into places where it isn't wanted. Controlled bursts were the key to effective cleaning. The can of Klima-Cleaner was good for several 5- to 10-second bursts.

The fins on the evaporator surface are very thin and will bend with the slightest pressure, so I tried to make as little contact with them as possible. I also sprayed the interior surfaces of the heater box around the evaporator to remove anything that might be clinging to them.

I made sure to keep the can upright while spraying, and I waited at least 30 minutes before starting the car to dry out the heater box.

Preventative Measures

Einszett recommends using Klima-Cleaner to clean the evaporator every three to six months.

To slow the return of the stink, I plan to continue doing what I've done for many years: a few minutes before I reach my destination, I turn off the A/C but continue to run fresh outside air through the vents to dry any condensation that may be clinging to the evaporator or inside the vents.


Here's one method I didn't use. Some products designed to clean a car's A/C evaporator include a long hose attachment along with the aerosol can. Vendors, touting the ease with which the product can be used, recommend that you snake the hose down the center vent as far as it will go, then unload the entire can of foaming cleaner into (hopefully) the heater box. Using an inspection mirror, I looked down the center vent and saw nothing but closed flaps. The flaps on my car's system close when I shut down the HVAC system, so I don't think it's really possible to access the evaporator this way. Your mileage may vary.

Of the two methods I used, both were pretty straightforward. Each one has its advantages and disadvantages. The parts I removed to get to the evaporator only went back together one way, so reassembly was hard to mess up. Both methods required roughly the same amount of time.

Method 1 is a no-brainer if you're also planning to replace a failed final stage unit, install a new radio, or do other wiring work behind the radio or the glovebox. But you need to be comfortable with working in such a small space and without a good view of most of the evaporator. Plus, if you have the on-board monitor, you'll have to think about getting the special tools to remove it.

Method 2 makes more sense if you have other work to do in the engine bay that requires removal of the microfilter air plenum, such as replacement of the blower, spark plugs, ignition coils, or the valve cover gasket. You'll find yourself leaning over the engine a lot, so plan on having a sore back afterwards. As I said before, I think Method 2 gives the most direct access to the evaporator surface, and it also offers the opportunity to clean the inside surfaces of the blower housing.

After reading all of this, you may be wondering how to clear a clogged heater box drain. I don't know the answer to that question, because the drain tube is located above the transmission and seems to be inaccessible. Anyone who has successfully cleared his or her heater box drain is welcome to post in this thread.




5,537 Posts
Great howto. I wonder if it would be easier going from the under the hood side where the blower motor is? I got a nice view of it when I was doing the trans swap on my 323i but didn't notice how far you can or cant see back in there.

121 Posts
Many thanks to G. P. Burdell for this excellent DIY

I performed this service yesterday, using Method 2. The procedure went very well.

Here are my notes:

In addition to removing those items in step 2B, I also removed both wipers and the long, plastic cowling under the wipers that seals the bottom of the windshield.

Instead of unclipping the blower retaining strap in step 2E, I opted to remove the four screws with integrated washers, after putting rags in the air channels to catch screws if they fell.

The blower motor and squirrel cage came out cleanly, without having to force it through a too-small opening. There was "just enough" clearance to remove it without resistance. This was very satisfying since I had heard of people using some force to get it out.

There was fuzzy mold growth on the evaporator fins in the bottom center. I used shop air to break up some of the mold. I then sprayed the entire surface of the evaporator, getting foam to all four corners.

When installing the motor I used Stabilant 22, which is an "electrical contact enhancer" mentioned many times in the Bentley manual, to coat the plug contacts.

I've included a few photos with notes that may help someone else who, like me, has never been in there before.


1 - 3 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.