`87 and newer 190 climate control help
 

I have been trying to figure out what is wrong with my push button climate control unit for a while now.

I knew there was an issue when my blower motor was cycling. The FSM provides some information on diagnosing it. The unit seems to think there is something wrong with the outside temperature sensor. But all my own tests, and the tests the FSM says to do says the sensor is okay. So I am stuck. Is my control unit bad?

Thanks for any help!

Oh and my dash is removed as I just replaced the pods and heater core. Want to get this working before I put the dash back in.

There is a small air vent just rear of your rear view mirror. Put a small piece of tissue paper next to it to determine if its pulling air. The small motor is behind the right most dash vent if not.

Since the dash is out, I can confirm that motor is spinning.

Can you clarify your issue?

Blower motor cycling? The 190's had manual blower motor control as far as I know.

I refreshed a W201 climate control for a member here a few months ago:
201 830 03 85 First Gen Climate Control W201 - Imgur

Yours might benefit from such a service. I dont remember the specifics of what was going on with the unit in the album but I do know that when it was installed it worked well. I do recall it having a few cold solder joints.

Additionally, the outdoor temperature sensor is unrelated to the climate control system. The only temperature sensors that the push button unit care about are the evaporator temp sensor and the cabin temp sensor

The 1987 and later models can sense issues and will click the blower motor on and off until it senses the issue is resolved. This comes from the FSM.

I have to disagree with you on the outside temperature sensor. The ambient temperature sensor is only for display but according to the FSM the outdoor temperature sensor is used by the push button unit.

I was trying to take mine apart to replace the caps and reflow but I cannot seem to get the wheel off. How did you do that?

Attached is FSM stating the diagnostic feature.

Thanks for the help.

Hm, I stand corrected. It looks like it uses it or at least monitors it in some way.

I've never had my 93 do anything with pulsing the blower though. But then again, I've never had any problems with it out side of a disconnected vacuum line.

My outdoor temp display was fixed for a bit then went out. I think it lost connection to the sensor. But if the PBU still has connection (since its not pulsing the blower) I can assume the sensor is good.

Hm I would start with a reflow and re-cap of the PBU. Its not going to hurt (unless you somehow damage it or bridge things)

There are multiple wheel configurations that I've run into. Some are held in by a pin on the side that you squeeze and pull. Check out that album or some of the other climate control ones on here my imgur account here JamesDean59's albums - Imgur One them is bound to give you an idea of how to take out the wheel.

The MBs of that era had two outside air temperature sensors. One in the bumper for the dash display and the other in the air intake plenum under the hood for the climate controls.

The control equation needs to know the following variables to be able to regulate:
- outside air temp
- cabin air temp
- evaporator temp or heat core temp
- setpoint from the wheel

I guess your unit has never sensed a fault with a sensor then.

There are two different outside temperature sensors. The one the PBU monitors is by the blower motor. The one for the display is under the license plate.

I will take a look at removal of the board for reflow and re cap and I will keep you posted.

Attached is the FSM page where it talks about the relay clicking.

I guess not which is impressive, at least to me. I can only remember two problems

1) Complete loss of blower/air movement on the way home once which was remedied by cleaning out the evaporator. There was a blanket of muck covering the whole thing where the fan blew across.

2) Head at the side vents. This was caused by me accidentally disconnecting the vacuum line next to the brake booster.

I had planned on reflowing and recapping my 190's unit one of these days..just because I'd never done it.

Hopefully it fixes your issue or at least helps.

Okay I got the board out and attached is a picture. Do you know what the specs of the big capacitor is? It looks like it is the same one that was on your board.

Are you talking about the sensor in the bumper or the one in the blower case? The one in the bumper ONLY connects to the display. I think you need to check the one in the blower case.

Have you tried disconnecting the aux water pump? That's the usual cause of this.

Yes, I knew to check the one by the blower case thanks to the FSM.

I did disconnect the aux water pump and unfortunately it did not resolve my issue.

The one I replaced it with was 1,000 uF 40V axial capacitor.

Specifically, this guy:
MAL213817102E3 Vishay / BC Components | Mouser

Darn. I thought it was a 470uF.

Thanks!

I'd pull it out just to be sure. The one I did was 1000uF. The one in your pic is just about as big too.