Close heater control valve for summer to maximize AC - Page 2 - PeachParts Mercedes-Benz Forum

Cr from Texas · #1 06-11-2008, 07:31 PM

Quote:

Originally Posted by Jeremy5848

An additional monovalve problem that can also cause those same symptoms is a partial failure of the rubber parts inside the valve. This causes coolant to invade the electromagnet area and cause the valve to be sticky. A kit is available to replace this part of the monovalve.

I've probably installed about a dozen monovalve kits in this car and knew to look for rubber damage - none. I think the complete valve replace has solved my problem. Does everyone realize Bosh has stopped production of these? Better buy a spare while you can.

I also found some monovalve kits are defective and use the following test procedure when installing:

Put the kit into the electromagnet portion and connect the pins direct to the battery to get 12V. A good kit will extend about 15-20 mm and hold that position until the voltage is removed. I found some kits (cheaper, probably from China). That pulse open and closed in my test. Clearly these would not be acceptable. I had two bad ones that I could not returned so I switched out the rubber pieces.

pwjeep · #2 06-11-2008, 10:10 PM

My '85 123 has hot flashes when the AC is on. The 134 AC seems to cool well until some component thinks it's time to flake out and then it's 120+ degrees blasting out of the air ducts. Then after about 10 minutes of baking on high heat, the AC cycles back on and cold air returns. It's really annoying.

I was thinking of bypassing the monovalve with a dual valve set-up which would take the heater core out of the loop when I set the valve to bypass. I would add 1 hose between the new bypass and the output which goes to the engine. Yeah, I know this would mean no heat when the valves are in bypass mode, but I'm tired of this gremlin stuff.

Has anyone tried a bypass like what I've described?

SD Blue · #3 06-12-2008, 11:53 AM

Quote:

Originally Posted by Cr from Texas

I've probably installed about a dozen monovalve kits in this car and knew to look for rubber damage - none. I think the complete valve replace has solved my problem. Does everyone realize Bosh has stopped production of these? Better buy a spare while you can.

I also found some monovalve kits are defective and use the following test procedure when installing:

Put the kit into the electromagnet portion and connect the pins direct to the battery to get 12V. A good kit will extend about 15-20 mm and hold that position until the voltage is removed. I found some kits (cheaper, probably from China). That pulse open and closed in my test. Clearly these would not be acceptable. I had two bad ones that I could not returned so I switched out the rubber pieces.

Hmmm......this sounds like a major factor in marginal air conditioning. I have noticed that sometimes the a/c puts out pretty cool air and at other times it's barely there. I'll have to look into that when the leaking vacuum pods are resolved. Also, I was unaware of the check valve. Does the check valve portion look like cleaning would be any benefit or is it pretty much remove/replace?

Jeremy5848 · #4 06-11-2008, 03:04 AM

I believe it is part of the monovalve but unfortunately not the replaceable part for which you can buy a "kit." AFAIK, you have to buy the entire monovalve.

Cr from Texas · #5 06-11-2008, 10:56 AM

I had a complete new spare monovalve that I just finished putting in so I'll see how that goes.

On the old one, I guess the part at the bottom is the check valve. I can use the garden hose and flow water through it both ways. I guess that means the check valve was bad.

#6 06-11-2008, 01:16 PM

Quote:

Originally Posted by Cr from Texas

I had a complete new spare monovalve that I just finished putting in so I'll see how that goes.

On the old one, I guess the part at the bottom is the check valve. I can use the garden hose and flow water through it both ways. I guess that means the check valve was bad.

Hopefully that was the problem, let us know how it works.

JohnS · #7 06-11-2008, 02:11 PM

You're supposed to have some heat in the heater core - that gives you humidity control or reheat. Without that you will have cooler, saturated air, which is not optimum for comfort. In Texas it may be so hot that this is not a factor, but in areas where humidity is very high, like the east coast, it makes a big difference

tangofox007 · #8 06-11-2008, 02:26 PM

Quote:

Originally Posted by JohnS

You're supposed to have some heat in the heater core - that gives you humidity control or reheat. Without that you will have cooler, saturated air, which is not optimum for comfort.

Tell us, John, where does that moisture go after the heater core boils it out of the air?

Bajaman · #9 06-11-2008, 02:31 PM

It's true that these systems were designed to remove water from the air by cooliing it then reheating it to the proper temperature. But that is only useful in cool humid weather. In the summer just cooling the air should be fine. I'm sitting here freezing in my building because the steam is down. It's 80* outside. Some idiot decided that we need Very dry air in this building... What a waste of energy.

Cr from Texas · #10 06-12-2008, 09:45 PM

Sam,
I just learned about the check valve from an earlier post. When I removed the entire assembly and looked in at the bottom end, I could see what must be the check valve. It's in the large end and you can tell it was assemble with some type of fastener. I did not try to take in apart. I did try flushing it with WD40 without any success. It's now on my parts shelf for one of those "do it later" projects.

I was surprised by the faulty core pieces and don't understand how they could pulse like they did - but they did!

#11 06-12-2008, 09:55 PM

I've never tried to take the check valve apart either, but I believe it's only function in to prevent back-flow into the heater core when the monovalve is de-energized with the car shut off. When the engine is running, the water pump should not allow back-flow anyway.

SD Blue · #12 06-13-2008, 10:58 AM

Quote:

Originally Posted by Craig

I've never tried to take the check valve apart either, but I believe it's only function in to prevent back-flow into the heater core when the monovalve is de-energized with the car shut off. When the engine is running, the water pump should not allow back-flow anyway.

The reason I'm a little suspicious is for a couple of reasons. The a/c, on occasion, is only moderately cool and in the winter I can hear the heater core filling with water when heat is turned on. With mention of this check valve, I wonder if the two are related?

#13 06-13-2008, 11:10 AM

Quote:

Originally Posted by SD Blue

The reason I'm a little suspicious is for a couple of reasons. The a/c, on occasion, is only moderately cool and in the winter I can hear the heater core filling with water when heat is turned on. With mention of this check valve, I wonder if the two are related?

That is strange, but I don't see how the check valve would be the cause. Also, I never hear my heater core; I wonder if you have air in the system someplace. If the AC system is working (compressor is engaged, top AC hose is cold), I would still suspect that the monovalve is letting hot water into the heater core under some conditions.

Cr from Texas · #14 06-12-2008, 10:01 PM

I wonder if the failure is due to my choice of coolant. I've always used Zerex and only recently learned reading this forum that the preference is a red MB coolant. Is that a dealer only item?