Evil Servo Question - PeachParts Mercedes-Benz Forum

sknaffl · #1 10-30-2009, 01:34 PM

So..I had a cracked cc servo in the 116 and the PO had bypassed the system. I found what appeared to be a good used unit at my local pull a part and pulled it. I took it apart and all the seals seemed to be in good shape.

I did notice however that both on my old unit and the new unit the aux. water pump was seized. I tried hooking it up directly to the battery and nothing happened, plus the impeller seemed stiff to turn.

After I hooked everything up to the new unit, everything worked properly as far as the vent control. Center flaps work, defrost, fan, etc....but I have no heat.

So after this background info I have three basic questions:

1. Is it required for vehicles fitted with the cc servo set-up to have the aux. water pump in working order to push coolant through the valve?

2. I hooked a voltmeter up to the power supply to the water pump and got 12 volts on full heat and defrost....theoretically if I switched the control to auto lo and moved the temp gauge to cool the power supply to the water pump should cut out right? ...because mine does not, it maintains 12 volts.

3. If I have a fried amp I wouldn't be getting vent control..right? Or could that be an issue as far as switching the servo from hot to cold?

I've searched for hours through the numerous posts on this issue, but could not find any answers to my questions above....

Thanks for the help!!

Sam

kerry · #2 10-30-2009, 02:05 PM

I think I can answer #1. No. You should still get heat even without the aux pump operating.
I'm under the impression that the aux water pump is functioning all the time. I could be completely mistaken on this.
It seems likely to me that with a frozen pump, the amp is fried. I'd get a used amp, plug it in and see what happens, If that's not the problem, you then either have a spare or can sell it to someone here.
All that being said, the servo should default to the defrost position so that at least you get heat. So the fact that you're not getting heat in defrost is puzzling.

Graplr · #3 10-30-2009, 02:11 PM

Quote:

Originally Posted by sknaffl

So..I had a cracked cc servo in the 116 and the PO had bypassed the system.

Quote:

Originally Posted by kerry;

So the fact that you're not getting heat in defrost is puzzling.

The fact that the PO rerouted things may have something to do with this. Are you sure HOT coolant is now flowing into the heater core? I am wondering if it has something to do with plumbing, more so that the buttons depressed.

But then again, I don't know much about the servos. All I know is the brief time I drove a 116 the heat worked as on or off and that was it.

sknaffl · #4 10-30-2009, 02:29 PM

Quote:

Originally Posted by Graplr

The fact that the PO rerouted things may have something to do with this. Are you sure HOT coolant is now flowing into the heater core? I am wondering if it has something to do with plumbing, more so that the buttons depressed.

But then again, I don't know much about the servos. All I know is the brief time I drove a 116 the heat worked as on or off and that was it.

I had considered the plumbing, but was very careful when removing the old system that everything lined back up.

I can feel the hoses getting hot running into the servo and the servo base itself is hot...I also feel heat on the hose coming out of the servo running into the top of the firewall, but it stops about halfway...causing me to think if the aux. water pump were running it would push it on through.

I'm actually packing up my tools to head back to pull a part to pull an amp and see if I can find an unseized water pump....

rrgrassi · #5 10-30-2009, 04:27 PM

Is the heater core plugged? Does this car have a monovalve?

kerry · #6 10-30-2009, 04:58 PM

No monovalve. Plugged core seems possible but a long shot. Don't see many plugged cores on here. I'm thinking something with the servo valve is not opening all the way.

sknaffl · #7 10-30-2009, 05:14 PM

definitely not plugged core....heat worked great when bypassed

I just picked up a new amp....maybe that will be the cure.

Or...my other thought still...is if the aux water pump is seized and the impeller won't turn at all maybe coolant is having a difficult time passing through the housing. Unfortunately no water pumps at my local pull a part. I have a couple of other places to try tomorrow.