Heating - PeachParts Mercedes-Benz Forum

tobybul · #1 10-12-2009, 07:59 AM

Its that time of the year and I'm wondering why the heating on my 84D is not as good as my 85D. It puts out about 1/2 the heat that my 85 does.

I'm guessing it might be the heater core as I've already checked the CCU and the heater valve.

Has anyone found a good way to clean out the core without taking it out? I have some ideas but I wanted to see what members have to say.

Thanks

Jeremy5848 · #2 10-12-2009, 11:42 AM

Have you checked the aux coolant pump?

tobybul · #3 10-12-2009, 12:48 PM

Quote:

Originally Posted by Jeremy5848

Have you checked the aux coolant pump?

IIRC, I believe I did but thats a good point. That shouldn't be too difficult to chk. IIRC, I just turn ignition switch to on (not starting the car), set the temp to heat, and aux pump should come on. This way you can either hear or feel the pump. Right?

If the pump works, my thought on cleaning the core was to pour a mild acid solvent into the core inlet at the firewall (after detaching the inlet and outlet cooling hoses and blowing out the coolant inside the core) and let it sit for a few minutes and rinse off. I used to do this on my 99 Taurus as the core would get dirty easily. The coolant quality of my 84D is very good that is why I am puzzled by this issue.

kerry · #4 10-12-2009, 01:29 PM

Bad aux pump is a common problem. Make sure you fuse it. Never read of a plugged heater core on here. Could also be a bad thermostat.

pawoSD · #5 10-12-2009, 01:59 PM

My dad's 82SD has the same issue, really weak heat....I'm thinking its the heater core on that car too....as the monovalve and aux pump work fine....

tobybul · #6 10-16-2009, 02:41 PM

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

Finally got around to checking the aux pump this afternoon. I checked it 3 ways. First turned on ignition key without starting car. Noticed no sound or vibration from ppump.

Next, unplugged pump power and connected directly to battery and viola!! wrrrrrrrrrrrrrrr. It works.

Next, connected volt meter to power supply side of pump with car running and set to heat. No power.

I can't imagine its the ccu thats bad b/c sometime back i swapped the ccu between my working-heat 85D and the 84D and my 85D is still spitting out heat like crazy.

Help!!!

rrgrassi · #7 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 · #8 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 · #9 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 · #10 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 · #11 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 · #12 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 · #13 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 · #14 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 · #15 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.