PeachParts Mercedes-Benz Forum - Strange W210 AC behavior

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Quote:

Originally Posted by dukegrad98 (Post 1501613)

Thanks, guys. I've been down looking at the car. The pinching off the heater hoses to the duovalve is pure, simple genius. Wish I'd read that before I took the whole thing apart, per ParrotofDoom's excellent instructions. The valve seemed fine. Plungers move freely, springs work, etc. I put it all back together.

While driving, I notice that diagnostic indicator #7 (low side pressure, I believe) was ranging between 11 and 13. At park or neutral, it showed readings 14 to 16. There is some "hissing" sound in the cockpit. The driver's side is blowing cool, but not as cool as the passenger's side. If I turn on the defroster for a 90-120 seconds, then back to air conditioning, the far left vent (left of the steering wheel) blows very hot air.

Does this additional info help? I think I've done all I can do short of dropping it off at the shop and telling them to make it right. Maybe a DIY can of freon? Yeesh. Thanks again for all the guidance on this new toy -- today has mostly been a disgusting one!

Cheers, John

Sorry, I inadvertently commented on your post and then had to delete it, John.

I think the Parrot of Doom instructions do not address the potential electrical failure of the actuator. In my car the electrical actuator acted like it was "tired" and would default to the open position on the driver's side. The instructions get the actuator off, so once it is off you can test it for continuity (Ohms) and possibly inductance. Not sure what the results should be, but you can start by comparing it to the side that seems to work all the time. I was not sure how to determine if the control system was at fault or the actuator was at fault. In the end the dealer replaced the duovalve and since then the system works fine.

Also, that hissing noise is pretty normal as far as I know. In the evaporator the liquid freon is given the opportunity to boil off as it comes out of the valve and sprays onto the heat exchange surfaces of the air cooling unit. This causes the hissing noise you hear as the heat exchange surface is in direct contact with the air venting into the car, and the surface is a very thin membrane to be more efficient. Jim

I just had that same problem with the vent temps. It turned out to be a leaking evaporator. It was expensive to replace but seems to be holding temp now. You need to fill system with die to ck for leaks and also use a snooper in the vents to ck for r134 loss...

after reading all through this thread it is my opinion that you have two probs.[1] bad heater valve [2] low freon charge[hissing noise and low side pressure readings big clues] replace valve and add freon [not too much] easy check is low pressure at 35-40psi [with in car temp at about 75-80f] and high side at about 250psi slowly going up and bringing on high fan which swings it back to 225psi.next hold engine rpm's at 1500-2000 and make sure high side does'nt climb above 325psi.

Duke,

What was your resolution and fix on this topic? Your comrades would like some feedback?

I forget what I've posted here already... The short answer is that I took apart and inspected the duovalve, and all seemed to be well. I picked up a can of refrigerant and a fill hose and added about six ounces of freon (134a), about two ounces at a time over a long period.

I now have cool air out of all vents. It has been about six weeks since this problem cropped up, and at least a month since I added that refrigerant, and I have not had a loss of cooling capacity yet. I know freon doesn't just go away without a leak, but I have no idea about the prior owner. Since I recharged the system a bit, things are well. I'll be keeping a close eye on it during the hot Texas summer!

Cheers, John