190D Bizarre Blower Behavior - PeachParts Mercedes-Benz Forum

bentrod · #1 04-16-2018, 05:30 PM

My 87 190D has a very odd bizarre blower behavior!
Here is the list of what it does and not:
The blower works ( you can switch speeds too ) with the key on and engine on EVEN IF the pushbuttons are off!?
When you go to the left most pushbutton windshield icebreaker the blower fan does not respond - just goes to where you have the fan speed switch located - no maximum high.
Now here is one more tid bit: The blower fan switch will make a CLICK, then stop blowing and then CLICK again and keep working. And then repeat.
It's a very consistent condition about every 2 minutes, regardless of key on or engine on. As if its on a timer ( ? )
I just got some reman pushbuttons and a used set - all the same conditions.
Tapping on components, wiggling the key or wiring harness has no effect.
Any clues?

bentrod · #2 04-17-2018, 09:10 AM

The blower control switch has 2 relays inside, soldered. That is what's clicking on and off.

Maxbumpo · #3 04-17-2018, 09:19 AM

I'm wondering if the power to the PBC goes through the ignition switch, and that is getting flaky. Try moving the key up / down / sideways, and gently twisting a bit, to see if you can influence the behavior of the power to the blower motor when the key is in the off position.

bentrod · #4 04-17-2018, 09:21 AM

Quote:

Originally Posted by Maxbumpo

I'm wondering if the power to the PBC goes through the ignition switch, and that is getting flaky. Try moving the key up / down / sideways, and gently twisting a bit, to see if you can influence the behavior of the power to the blower motor when the key is in the off position.

I'll try that.
Its extremely strange. It "cycles" on and off, like its on a timer??? It's very exact in its execution.

bentrod · #5 04-17-2018, 09:45 PM

Quote:

Originally Posted by Maxbumpo

I'm wondering if the power to the PBC goes through the ignition switch, and that is getting flaky. Try moving the key up / down / sideways, and gently twisting a bit, to see if you can influence the behavior of the power to the blower motor when the key is in the off position.

I wish this gave me a hint but so far no change.

Maxbumpo · #6 04-18-2018, 11:28 AM

I think you should spend some time studying the service manual to see if you can glean some ideas.

Random thought: Is the blower motor pulling too much power and causing a self-protection circuit to engage?

bentrod · #7 04-18-2018, 08:46 PM

Quote:

Originally Posted by Maxbumpo

I think you should spend some time studying the service manual to see if you can glean some ideas.

Random thought: Is the blower motor pulling too much power and causing a self-protection circuit to engage?

While that is an interesting question.. why is the fan working at all in the first place when the push button controller is switch off?! It's crazy.

bentrod · #8 04-19-2018, 06:23 PM

I found some info!
From the people at http://www.programainc.com
See attached:

My EXACT issue is..
Sympton:
When unit is off, fan stays on, or cycles on and off.

Test/Suspect problem:
Short circuit in sensor(s) and/or feedback potentiometer

(+) R pin 9 to ( - ) R pin 12 = pulsating voltage.

Interior temperature sensor = 5 pulses
Ambient temperature sensor = 10 pulses
Feedback potentiometer = 15 pulses
Evap temperature sensor = 20 pulses
Coolant temperature sensor = 25 pulses

Solution:
Replace sensor/switch

NOW......err, I just got to figure out exactly how or what I test this with LOL.
I'm assuming ( I know - don't ) you use a DVM and connect the pins as listed above, key on and set it to voltage. Or am I way off?

bentrod · #9 04-20-2018, 04:45 PM

Can some PLEASE confirm that the left (drivers side ) wiring harness connector for the climate control unit push buttons has the RED tape on it.

bentrod · #10 04-21-2018, 10:09 AM

***bump

bentrod · #11 04-22-2018, 05:33 PM

Moving right along...
The Programa test was incomplete, the CCU needs to be plugged in AND this car has NO wire in socket # 12!
This was a compound fix.
At first I needed as set of CCU push buttons. At the same time I was checking all the vacuum connections and had the instrument cluster out. This hvac system needs the cluster coolant temp gauge plugged in and it was not. Giving me that symptom of when unit is off, fan stays on, or cycles on and off.