Constant heat out of the side vents - PeachParts Mercedes-Benz Forum

dsvw · #1 10-02-2021, 03:07 PM

1986 190D here.

The side vents on my 190D constantly blow hot air.
If I close them off and turn on my a/c it blows ice cold out the center vents but I have to close the side vents or it will blow hot air.

It blows hot when the thermostat dial is at the coldest setting and the hottest setting...doesn't matter where it is.

I did have the gauge cluster out yesterday. Could I have disconnected a vacuum line?

Thanks in advance!

jetspeed · #2 10-02-2021, 04:21 PM

I'm COMPLETELY new to MB's and my 94' 250 D is doing the same exact thing. I found this link , HTH?????

https://www.*********.co/forums/threads/how-to-replacing-heater-valve-on-late-w124-non-v8-models-e-class-cars.3286/ (off of the 500 E border; link won't work here, google it yourself)

Recently, my wife started complaining of hot air coming out of the side vents of her 1995 E320 wagon, when she had the air conditioning cranked on, while (as appropriate) cold air was coming out of the center vents. Some research and deduction indicated that the heater valve (some incorrectly call this the "monovalve") was defective. Now, the 124.034 (400E/E420) and 124.036 (500E/E500) use the "earlier" W124 heater valve/monovalve design, but the non-V-8 W124s went to an updated, integrated design around the 1991/1992 model year.

Let's have a quick sidebar for you .034/.036 owners...... The "older" design as used in the E500E uses a separately mounted solenoid (monovalve) and auxiliary coolant pump (which keeps hot coolant circulating through the heat exchanger during times of low RPM, such as idle, to keep hot air flowing through the ACC system when the water pump isn't spun up). Because this is a separate, two-element unit, mounted in two different places (different sides of the CAN box on the 036) it tends to be a blessing and a curse. A blessing because generally only one of the elements goes bad at a time, and both are available separately. A curse because they are more difficult to get at due to their proximity to the CAN box. The fact that the elements are available separately means that they are also cheaper.

So, back to the task at hand ... 1995 E320 wagon. The heater valve on this car is an integrated unit that contains the aux coolant pump and monovalve mounted on a single base, with four individual hose connections. What's nice about this is that everything is VERY accessible (including three of the four hose connections) and the base mounts to the car with three rubber plugs, which simply press into place both on the base plate and onto slots in the car.

I ordered the part from parts.com, which was $207.00 (from nearly $300 MB list price) on Monday, and it arrived at my house on Friday morning. And I only had a 7.9% shipping charge, with some other small MB parts included in two separate packages. So tonight I decided to tackle the task of installing the valve. It took under one hour to do.

Here is the list of items required to do the job:

a roll of paper towels or a supply of 3-4 rags (to soak up coolant that spills from the hoses)
a piece of Saran Wrap
a long, flat blade screwdriver (for undoing hose clamps)
a pair of needle nose pliers and/or a small flat-blade screwdriver (for removing & installing the rubber mounting plugs)
a supply of coolant (to replace coolant if any is spilled)

Here's the procedure:

First, a couple of views of the area where you'll be working:
IMG_1638.JPGIMG_1639.JPG

Next, disconnect the two electrical connectors. They just pinch and slide off....
IMG_1640.JPGIMG_1641.JPG

Then, we get sorta crafty. What you need to do is to remove the coolant expansion tank cap. Then, carefully place your piece of Saran Wrap into the top of the tank's opening and replace the cap (carefully). This creates a vacuum in the system so that it's much more difficult for the coolant to spill out of the hoses, once you loosen and remove them from the valve. You'll lose a bit of coolant, but not nearly as much as you would if the vacuum were not present.
IMG_1642.JPGIMG_1643.JPGIMG_1644.JPG

After that's done, it's time to loosen the four hose clamps that attach the valve to the cooling circuit. Before you do that, wad up some paper towels or rags, and force them underneath the hoses and the valve itself. This will catch most all of the coolant that comes out of the ends of the hoses once you loosen and pull them off of the valve.

Two of the hoses are easy to get at. The third one is right on the other side of the inner firewall and also very easy to get at (on the engine side of the firewall).

The fourth hose is UNDER the one that goes through the firewall. It's best to loosen the other three hoses and the rubber plugs that hold the valve to the car; these actions free up the valve enough to turn a bit, so that its clamp is exposed to get a bite with your screwdriver. Once the clamps are loosened, and the three rubber plugs are pushed out of their slots, CAREFULLY remove the valve from the car by lifting it directly upward.
IMG_1652.jpg

Here is a shot of the area with the valve removed. You can see a couple of the slots where the rubber plugs slide into that mount the base of the valve assembly to the car.
IMG_1653.JPG

Then, it's time to unbox the new valve.
IMG_1646.JPGIMG_1647.JPGIMG_1648.JPGIMG_1649.JPGIMG_1650.JPGIMG_1651.JPG

And, a view of the new (left) and old (right) valves, side by side:
IMG_1654.JPG

Installation is exactly the reverse of removal. You will need to transplant the three rubber plugs from the base of the old valve to the holes in the base of the new plug. A very small flat-blade screwdriver is helpful for pressing the rubber flange of the plugs through the holes in the base of the old valve, and a pair of needle-nose pliers is helpful to pull the plugs up and through the holes in the base of the new valve.

Here's a photo of the new valve installed:
IMG_1655.JPG

Lastly, tighten up the hose clamps after reattaching the hoses, and uncap the expansion tank to remove the Saran Wrap. Start the car and test for leaks at the four hose connections. Then check the ACC system in A/C mode to ensure that the solenoid is closing the valve and keeping hot coolant out of the dashboard system, so that cool air circulates out of the side vents once again. If any coolant leaked out (it should probably leak about a half-cup or so) replace it with new coolant while you have the cap off to remove the Saran Wrap.
IMG_1645.jpg

If everything checks out, give yourself a pat on the back for a job well done, and have a beer. :deniro:

Cheers,
Gerry

ah-kay · #3 10-03-2021, 01:27 AM

Quote:

Originally Posted by dsvw

1986 190D here.

The side vents on my 190D constantly blow hot air.
If I close them off and turn on my a/c it blows ice cold out the center vents but I have to close the side vents or it will blow hot air.

It blows hot when the thermostat dial is at the coldest setting and the hottest setting...doesn't matter where it is.

I did have the gauge cluster out yesterday. Could I have disconnected a vacuum line?

Thanks in advance!

Hot or lukewarm air? I have the same problem with my 190D but it is lukewarm. I just close the vent and leave it like that.

You can try to check the hot water valve under the windshield. You need to remove a few trims to get to it. It is vacuum controlled, the default position is open. It is possible thete is a vacuum leak so the valve never closes or the CCU control electronic is faulty. Good luck.

dsvw · #4 10-03-2021, 11:47 AM

Thanks, I will check that valve for leaks.

dsvw · #5 10-03-2021, 11:47 AM

The air coming out is very hot.

dsvw · #6 10-03-2021, 08:18 PM

I checked the valve under the cowl and it holds vacuum.
I also heard a sound while applying vacuum as if a switch was activated.
The other side of the plastic tube also holds vacuum. I put a vacuum gauge to the side going into the engine compartment and did not get any vacuum with the engine running and HVAC running.

I also did not see any evidence of leakage around the valve.

Any ideas?

ah-kay · #7 10-04-2021, 12:41 AM

Quote:

Originally Posted by dsvw

I checked the valve under the cowl and it holds vacuum.
I also heard a sound while applying vacuum as if a switch was activated.
The other side of the plastic tube also holds vacuum. I put a vacuum gauge to the side going into the engine compartment and did not get any vacuum with the engine running and HVAC running.

I also did not see any evidence of leakage around the valve.

Any ideas?

If engine running and CCU calling for A/C then the valve should close ( control line has vacuum ). If no vacuum then either CCU is faulty or the relay bank ( behind the glove box ) is faulty.

I hacked relay bank on my 190D to physically activate the vacuum line. You do it at your own peril.

dsvw · #8 10-04-2021, 10:31 AM

Thanks, ah-kay, that is exactly what I have. No vacuum to the valve. There is also no leak in that line.

What does CCU stand for and where is it located? I could not find that part on Pelican.

And, the relay behind the glove box. Do you know what it's official name is? I couldn't find that part on Pelican either. A bunch of relays just show up.

I really appreciate the help!

ah-kay · #9 10-04-2021, 10:39 AM

CCU is the climate control unit, in center of console. Don't know the part number of the relay bank. Replacing them is expensive new, $400+ and it may not solve the problem.

Get them from junkyard. Alternately, just block the hot water flow using a clamp.

dsvw · #10 10-04-2021, 12:03 PM

I can't seem to find a relay bank listed online for my 1986 190D.
if it is the only relay back there, I will just pull out the glovebox and try to find it and a corresponding number. Thanks.

ah-kay · #11 10-04-2021, 01:10 PM

Quote:

Originally Posted by dsvw

I can't seem to find a relay bank listed online for my 1986 190D.
if it is the only relay back there, I will just pull out the glovebox and try to find it and a corresponding number. Thanks.

They are vacuum relays, a few of them bank together to control the pods etc. Just follow the vacuum line ( green or green plus other colors ) and you will find it.