Air Conditioning and Climate Control - PeachParts Mercedes-Benz Forum

Marvin Smith · #1 05-29-2002, 07:19 PM

I have a 1986 300SDL and took it to the shop to have the air conditioning checked because it was not cooling the car. The mechanic checked it out and said the compressor was working and everything was ok in terms of the amount of coolant. However, he said the heat and air conditioning were both on at the same time. What could cause this? Help!

euro 287 · #2 05-29-2002, 08:10 PM

If you grab the low side outside under the hood and it is cold but not inside the car , you either have a heater mono valve problem or fresh air doors wide open.Usually fresh air doors wide open you will also have a/c blowing from defrost due to actuator problems. First pinch off the heater lines with a pair of needlenose vise grips.If no effect than put the car on recirculate mode and then remove glove box and see if the fresh air doors are closed.

Gilly · #3 05-30-2002, 12:30 AM

Hi Marv, how's it going?
Sounds like possibly our ol' pal the mono-water valve insert. it's a little tougher to check on a 126. It's between the 2 firewalls, more on the passengers side. Has a 2 wire connector, a silverish button in the center, and it's held together by 4 slotted screws. Remove the connector, relieve pressure in the cooling system (remove pressure "radiator" cap) then remove the 4 screws. Pull the guts out by the silverish button. You need to carefully inspect the rubber bellows by carefully pulling on the center rubber seal, your looking for a tear in the bellows(the outer rubber section, below the smaller rubber seal). The bellows is available seperately as a "mono-watervalve repair kit". If you need info to replace it, let me know, but it's all pretty easy.
Gilly

Billybob · #4 05-30-2002, 05:09 AM

Go here for a step by step with pictures R&R for a 126!

http://mbdieseldiy.tripod.com/index.htm

Marvin Smith · #5 05-31-2002, 05:34 PM

Message to Gilly:

I bought a monovalve kit and must have installed it incorrectly. I took the car out on the road assuming the air conditioner was repaired. The car started to overheat and there was a lot of heat coming from the vents. A quick check under the car revealed that I was losing a lot of anti-freeze. I managed to return home OK. However, the only thing I can think of that I might have done wrong during the installation of the kit was to put the metal washer in the wrong place such that there wasn't a good seal between the valve and the seat. What is the proper placement of the metal ring? Help!

Gilly · #6 05-31-2002, 09:23 PM

Marv:
The site that BillyBob has on his post, I went to that last night. It's easy to find it, it has good pictures.
MB gives you a new wave washer, you reuse the 2 flat washers. The wave washer goes between the 2 original flat washers.
Gilly

Marvin Smith · #7 06-01-2002, 05:49 PM

Message to Gilly:

Thanks for your prompt reply. The pictures from Billy Bob were very good and please thank him for his help. After taking a look at the pictures and the car, it seems as if the small flat washer in the monovalve assembly was inadvertenly dropped and lost. I'm keeping my fingers crossed and hope you can tell me the size of the washer so I can pick one up.

Thanks for your help.

regards,

Marvin Smith

Gilly · #8 06-01-2002, 10:55 PM

Boy, no idea. Dimensions I would say should be the same as the wave washer they give you. Possibly the old one is on the old water valve insert? You also didn't tell us if the old water valve insert has a tear in it or not.
Gilly

Marvin Smith · #9 06-03-2002, 03:22 PM

To Billybob:

Your pictures were great and they helped a lot. However, I have a problem - the small flat washer shown in the Mono Valve assembly sequence was dropped and lost. I went to the Mercedes Benz dealer to get one of the washers and was told that they don't have one nor do they know the dimensions of the small flat washer. Do you know what size the small flat washer is and whether you could find one? I need the inner and outer diameter of the washer plus the thickness and material type. Please advise.

thanks,

Marvin Smith

Billybob · #10 06-03-2002, 03:43 PM

OK, this procedure is so easy I'll just go open up my monovalve and get the washer and measure it!

The washer is 1 MM/.04'' thick, it's 30 MM/1.180" O.D., and the hole is 18 MM/.710" I. D.

It appears to be plated steel as a magnet will hold to it, but I suppose it could be a magnetic stainless of some sort.

P. S. no i don't know where you could get one, I would try a good old fashioned hardware store, or an industrial fastener place. Or you could visit a pick and pull boneyard and get one and start your collection of other small pieces and parts! Maybe the dealer or a foreign auto parts place, now that you know the proper specs, just take your vernier calipers with you and measure till you find the right one!

Marvin Smith · #11 06-10-2002, 10:52 AM

This message is for Billy Bob:

Thanks for your advice. I finally located a monovalve assembly complete with the washers that I needed at the local junk yard. I was previously told that the wavy washer was sandwiched between the large flat washer and the small flat washer on the assembled monovalve. The assembled monovalve that I got from another diesel had the large flat washer on the top next to the magnet, small flat washer next and then the wavy washer on the bottom of the monovalve. I assume the order of the washers is important - please clarify.

thanks,

Marvin Smith

Billybob · #12 06-10-2002, 04:13 PM

Hello Marvin, all I can offer is the DIY site write-up pics. I did that write-up when I did my monovalve and on my 87 300SDL 126, the wave spring was between the two washers when I opened mine up so I put thigs back in the same order and thus far it has worked as expected so I would reccomend that way! Fortunately as you are probably now aware this procedure is pretty easy so you can try both ways and figure out the best way for your vehicle! Glad you could make use of the DIY site (it was TXBill's idea and effort) and good luck!

Marvin Smith · #13 06-10-2002, 05:01 PM

Greetings Billy bob:

Thanks for your prompt reply. I will try using the monovalve with the wavy washer sandwiched between the two flat washers as you suggest.

thanks,

Marvin Smith