2005 CLK 320 - Undergoing Major Service

Down to the basics now. What I am finding is that two of the stepper motors have failed, the gears inside are broken. One doesn't move at all and the other clicks. While I am here, I bought the kit from the dealer to replace all of the control levers and arms. No way I am going to button up this 2005 model with original plastic components.

Overall, this is not a bad job. It is series of small tasks all done in the proper order. I suggest doing this 1.5 hours at a time and stop if you get frustrated. I also recommend completely removing the crash bar from the dash as trying to drill through it and rig some work-around takes more time that removing the bolts that hold the crash bar to the vehicle's body.

Some will disagree but I have NEVER and I repeat NEVER worked on HVAC boxes without removing the crash bar. Cutting or drilling holes in the crash bar is totally stupid. I had the crash bar completely out of the vehicle in about 40 minutes this morning.

At this point, 10MM socket, 13 MM socket, T20 torx and some assorted hooks to get it done.

Here's my latest update.

After removing the dash and diagnosing the two bad stepper motors, I've decided to replace three of them - the defroster (which was toast), the footwell flap (which was clicking) and the one that moves the center vents open/closed (still working but right there in front of me). My cost on the stepper motors is $134.30 each (part 203-820-16-42) . I guess if any of the other three fail, I'm pulling the dash again but it isn't the end of the world. The others appear to be fine, for now.

Testing the evaporator core for leaks, I found none. I disconnected both drain tubes and used my electronic leak detector pushing it up inside the box, it was clear of any refrigerant. So, I guess that saves pulling the HVAC box out which is somewhat of a relief. I did find the Schrader valves on the system to set off my leak detector so at some point I will recover the system, change the valves, change the dryer insert and refill. Not today, though.

Looking at the coolant leak, I found it at the circulating pump near the coolant reservoir. It shows signs of coolant so I am replacing that item $205.40 (part 203-835-01-64). Due to the age of the vehicle's coolant reservoir, I'm replacing that too and the new one comes with a new sensor installed $43.45 (part 203-500-00-49). .

While I was in the cooling system, I replaced the plastic coupling at the firewall which can break after this age. It wasn't that bad of a job and the hardest part was decoupling the hose that connects from the engine to the coupling. A bit of silicone spray lube helped those parts separate for service. $29.60 (part 203-830-03-96-64). Attached is a photo of the new part installed.

UPDATE

I diagnosed the problem to be two of the electric motors and did replace the three that are the most used. Since two of those three are failing, I replaced the three that are most used.

Defroster Flap Motor - It was totally toast. It is a direct drive without linkage, just a small plastic piece between the motor's drive and the air box.
Footwell Flap Motor - It was clicking. It has linkage and arms that move the flap.
Face Vent Flap Motor - It was working but replaced as preventative. All of the plastic gears and levers were also replaced in the pic.

My CLK has the system where you control the temperature per side but the airflow is common between the sides. There are a total of six motors. The other three which I did not replace are as follows.

Left Blend Door Motor - Controls the air temperature for the LH side.
Right Blend Door Motor - Controls the air temperature for the RH side.
Recirculating Door Motor - Controls fresh air versus recirculated air.

I synchronized all of the motors with my scan tool and tested everything after installing the new motors. Everything works just fine. Now, it is time to reassemble the vehicle.

CONCLUSION AND RECOMMENDATION

With the age of these vehicles, expect to remove the dash. While this does seem to be a daunting task, the dash is actually not bad to remove. It is a series of small steps, not a difficult task. If you download the factory repair sequences, the job is very straight forward.

I took the entire task and laid out the repair sequences as Step #1, Step #2, etc. Each of the PDFs that Mercedes publishes on the job contain subroutine references and I ordered all of those in the order that the job is done. That saved me a couple of hours' time.

I did see some videos where the person is working around the crash bar and even one where a hole was drilled in the crash bar to access a screw. I consider that type of repair to be nonsense, butchery and very Billy-Bob. The total time to drill the hole, work around the crash bar and the inconvenience associated is greater than the 40 minutes to simply remove the crash bar. Don't be a Billy-Bob, remove the crash bar.

Lastly, when doing these repairs, I recommend the flap lever kit that has the plastic gears and levers that are between the motor's drive and the air box. It is pretty inexpensive and now is the time to replace those items.