Heating - PeachParts Mercedes-Benz Forum

rrgrassi · #1 10-16-2009, 03:00 PM

Fuses? Did you put a fuse inline with the Aux water pump? Also did you check the amp draw on the pump while you had it running?

tobybul · #2 10-16-2009, 03:21 PM

Quote:

Originally Posted by rrgrassi

Fuses? Did you put a fuse inline with the Aux water pump? Also did you check the amp draw on the pump while you had it running?

No, I did not do any of that....

But here's what I read in the FSM disk that I have... supposedly, there is a temp switch located behind the glove compartment that controls the pump. I'm wondering if the switch is bad.....

tangofox007 · #3 10-16-2009, 03:38 PM

Remove the power to the monovalve. If that doesn't give you way more heat than you can stand, then your problem is not a control issue, it's most likely a problem with coolant circulation.

The temp control regulator does not function when the temp selector is in a "detent" position. So. if selecting maximum temp of the temp selector does not give you lots of heat, the problem isn't the regulator.

Quote:

Originally Posted by tobybul

Now I know why my heating is marginal. The aux pump is not running because there is no power going to it. You were onto something, Jeremy

Unless it's obstructed, an inoperative aux pump isn't much of a factor except at idle.

tobybul · #4 10-16-2009, 07:07 PM

Quote:

Originally Posted by tangofox007

Remove the power to the monovalve. If that doesn't give you way more heat than you can stand, then your problem is not a control issue, it's most likely a problem with coolant circulation.

The temp control regulator does not function when the temp selector is in a "detent" position. So. if selecting maximum temp of the temp selector does not give you lots of heat, the problem isn't the regulator.

Unless it's obstructed, an inoperative aux pump isn't much of a factor except at idle.

Tango, which regulator are you referring to?

tangofox007 · #5 10-16-2009, 10:27 PM

Quote:

Originally Posted by tobybul

Tango, which regulator are you referring to?

The temperature control regulator. Which is what I presumed you were referring to when you referenced "the temp switch located behind the glove compartment."

tobybul · #6 10-20-2009, 09:02 AM

I removed the power to the MV but that did not do much. I still think that its because the aux pump is not powering. It would be good to know what powers the pump.

My ccu should be working as I swapped it sometime back from my 85D which had a working ccu - and my 85D has excellent heat using the ccu from the 84D - which means there was nothing wrong with the the ccu of the 84D.

snookwhaler · #7 10-20-2009, 03:23 PM

I was fiddling with this over the weekend. Here is what I found on my 85. Simply sliding the wheel to heat does not turn the Aux. pump on. The wheel has to bee all the way to full heat and in the detent for the pump to run.

I also found that the only other time it runs is when the defrost is on. The rest of the time it is off.

I verified all of the above with a meter as well.

Graplr · #8 10-20-2009, 03:34 PM

Quote:

Originally Posted by tangofox007

Unless it's obstructed, an inoperative aux pump isn't much of a factor except at idle.

I disagree. It makes a difference for me. Instead of fusing it I decided to put it on a switch. With it on the vent temps are a good 10-20F higher than it is with it off at highway speeds.

To the OP-
If you can't get it operational, run a switch to it on its own circuit. Or just wire it directly to the battery to see if it makes a difference for you while taking it for a drive. Then you can decide if you want to run a wire into the cabin.

tangofox007 · #9 10-20-2009, 03:52 PM

Quote:

Originally Posted by Graplr

I disagree. It makes a difference for me.

I am sure that every car has it's own set of characteristics. If I disconnect my monovalve power, I get way more heat than I can stand. And that is with the aux pump not running.

There are plenty of cars that are not equipped with aux pumps and their heaters work just fine. If the belt-driven water pump isn't pumping adequate coolant at highway speeds to provide heat, there seems to me that there has to be a problem greater than an inoperative (or non-operating) aux pump.

I think I would be swapping monovalves and backflushing the heater core.

tobybul · #10 10-20-2009, 10:09 PM

I understand what you are saying TF. However, the aux pump does matter with the W123s. Thats the reason why MB put it there.

I'll try what you suggested Graplr, to power the pump separately.

tangofox007 · #11 10-21-2009, 10:34 AM

Quote:

Originally Posted by tobybul

I understand what you are saying TF. However, the aux pump does matter with the W123s. Thats the reason why MB put it there.

The aux pump "matters" when it comes to having consistent heat at low engine rpm's. The belt-driven water pump should have no problem whatsoever providing adequate coolant flow at highway speed. If it could not, would it not stand to reason that MB would have designed an aux pump into the engine cooling system as well?

There have been a number of reports on this forum where members bypassed their aux pumps with good results. I am not buying the notion that an inop aux pump can cause a major degradation in heater operation if everything else is operating normally.

Graplr · #12 10-21-2009, 10:00 AM

Quote:

Originally Posted by tangofox007

I am sure that every car has it's own set of characteristics.

Agreed.

Quote:

Originally Posted by tangofox007

If I disconnect my monovalve power, I get way more heat than I can stand. And that is with the aux pump not running.

Perhaps climate makes a difference. It gets a bit colder up here. Way more heat than I can stand is a relative statement. My wife can never get enough heat in my car in the winter while I am plenty warm after about 15 minutes of driving.

Quote:

Originally Posted by tangofox007

There are plenty of cars that are not equipped with aux pumps and their heaters work just fine. If the belt-driven water pump isn't pumping adequate coolant at highway speeds to provide heat, there seems to me that there has to be a problem greater than an inoperative (or non-operating) aux pump.

I think I would be swapping monovalves and backflushing the heater core.

I've swapped monovalve with a new one and done several coolant flushes over the life of the car. No changes in my heat output. And I run around all winter WITH the monovalve unplugged. The best thing I did for me was to put the pump on a switch. I guess the only thing I haven't done is put a new water pump in but I have had two different engines in the car since I've owned it (thus two different water pumps) and the heat output has been the same so I don't think that is the problem.

So in my car, the pump manually switched on gives me the best heat in the winter.