Help with 89 190D Climate Control Troubleshooting
 

Trying to do as much as I can on the 89 190D my friend just bought before I send it over to my mechanic. When I got the car I observed that the climate control was completely non-responsive. Seeing that the blower motor fuse was blown, I replaced it. Still no response from climate control, but I noticed that, when I turned the fan on, there was some current draw (the lights dimmed).

From that symptom alone, can I conclude that either the blower motor and/or the regulator is shot?

When the blower and/or regulator shorted out in my W124 (can't be sure for certain I guess, as I replaced both at the same time) I would get a draw but no air. On occasion I was getting a high-pitched whine from the center vent area, where the blower is on the 124, but no air.

On the 89, it doesn't look like there's a regulator as such....it looks like it's just the slide switch and the blower itself.

Is the blower coming on, or no? One concern is that the fan isn't installed correctly and is interfering with the case. A few pointers:

- To get to the fan switch or climate control unit, you have to remove the radio console section and undo them from the back. You can't pull them out with dash hooks, don't even try it. To remove the center console, first pluck out the center vents by positioning them perfectly horizontal. Then use two pairs of pliers, one on each end of the center fin, and pull the vent straight back. Once the vents are out, you will see two screws that need to be undone. To get the bottom, take out the ashtray, and undo the two screws that hold the ash tray surround in place.


- The relay for the fan is built into the switch. Really. Speed control is by a group of resistors, not a solid state circuit. I don't remember where they're located.

- There's an interesting feature in these later 190's. If the aux water pump fails, there's a circuit breaker inside the cc unit that goes off and shuts down the whole system. It's automatic, so if the bad pump is unplugged, it will automatically reset and the system will come back. I always start with that, it's a five minute test.

- If you really want to be scared, take a look at how far I had to go to fix mine:

190 Restoration

- There's a popular online reference for the 190 tempmatic here:

Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System

No, the blower isn't coming on at all.

Thanks for the resources, Mxfrank. I had forgotten about the aux pump shut down....I will check that next.

Disconnecting aux pump has no effect. So, since there is current draw and no regulator, can I conclude that blower motor is shot?

It's a good bet. It's easy enough to remove the motor to check. Remove the wiper, drainage tray and weatherstripping below the windshield. Undo the sheet metal screws that hold the rear sound barrier in place (you may have to remove some wiring that's clipped to the barrier. Push the barrier forward and undo the clips around the motor box cover, remove the cover. Undo the clip that hold the motor in and unplug. Lift out motor.

I have a tired but functioning fan motor if you need one.

With or without the squirrel cage assembly?

Complete. You can have it for postage, pm if interested. It's well used, but still runs.

Sounds good...I'll PM you.

Fantastic work and links, thank you :)

Not sure if I should add to this thread or start another......
My 87 190D just had the heater core changed, and here we go!
I only get full heat, no cool air ( center vents not apply = Tempmatic system )
Quick check list:
Aux water pump was and still is unplugged.
I have good vacuum source at the switching valves.
Cabin sensor, aspirator motor is clean, drawing in air.
Confirmed the full heat is because the heater valve ( tested - holds vacuum ) tube gets no vacuum 98% of the time, regardless of button and temp wheel settings UNLESS you press the re-circulation button?! Gets about 8 inches. And does get full vacuum at the heater valve when you switch off the engine.
Is the crazy?
Also - I do have a good used climate control unit that I tried - exact same crazy function with the re-circulation button?!

I check out...
Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System
But seems a bit vague to me.
I hope someone can steer me in the correct direction, thank you.

The heater valve will almost always be fully opened. In this system, heat regulation is done by an air blend flap at the top of the heater box. Cold air is blended with hot air to yield your set temperature. The system is designed so that any failure leaves the blend flap in the fully hot position. So hot doesn't tell you anything about where the problem is. In fact, even a vacuum leak anywhere in the engine compartment will give you full heat all the times...in 427,000 miles of driving, the most frequent fail point for me has been the little rubber vacuum connector on the EGR valve.

The most important thing to do is to make sure you have full vacuum at the switchover valve. This is located behind the dash, about where the passenger's knee would be. Easiest way to reach it is by removing the glove box liner, but it can also be accessed from below by removing the underdash plastic panel. If you have good vacuum there, then there are four likely culprits:

- the switchover valve itself. It's possible to test this, but it's very hard to explain how, and you'd need to cobble up some gadgets. Easier just to replace the switchover, if you can find a cheap one.
- One of the vacuum pods behind the dash, or the vacuum pod that operates the heater valve. You can isolate the lines at the switchover and test them with a mityvac. Replacement of anything but the heater valve requires removing the dash.
- One of the sensors, most likely the blend flap potentiometer. The other possible would be the cabin temp sensor, which is located near the rearview mirror. On that, it's piped back to a tiny sampling fan located just to the right of the glovebox. Sometimes the foam connector deteriorates, and needs to be replaced. So that's one more reason to go in through the glovebox.
- The push button control unit itself can be failed.

Good luck, this is a terribly complex system and the group grope will be of limited help. The deeper the problem, the more complicated the solution and the more creative you will need to be with testing. The links I supplied have flaws, but remain the best online resources. You will also need the shop manual, which has an entire section devoted just to this.

The EGR is deleted.
And I did try another set of push buttons and have vacuum at the switchover valves.
I'll just have to try each one of the lines from it and see what I find.