Strange W210 AC behavior
 

Honest, I searched and read a bunch of air conditioning threads before posting this. It's starting to be summer here in Houston -- temperatures creeping toward 90. I have a new-to-me '98 E300 Turbodiesel sedan. The AC seems to be working and blowing reasonably cold. The automatic climate control seems to be doing its thing...though it never does make it up to the max fan speed. Huh.

The real issue is a difference in temperature between the sides of the car. It has "dual zone," but I've never been much of a believer in that. No matter what I set the two temperature selectors to, the driver side vents are notably warmer than the passenger side vents. It's so noticeable that you can tell a difference in the two center vents above the console -- the passenger one will feel very cool, while the driver one is significantly warmer (but still cooler than ambient).

Anyone know what's going on here? I was hoping for an easy shot of refrigerant, but I'm concerned this might signal a slightly deeper problem. Any tips much appreciated.

Cheers, John

that symptom does usually indicate low freon

Permit me to provide some more info... I figure the more I tell you guys, the more you can help me. :) I just took a fifteen-minute drive and went through some of the built-in climate control diagnostic readout stuff.

First off, reading #5 (evaporator temp) never got lower than 17, and hovered around 20 most of the time. I think that's degrees Celsius -- so my evaporator is only about 65-68 degrees? No wonder my car won't cool off enough! Reading #6 (ECT sensor?) was reading out 84. I didn't write down more of the codes, but would be glad to if it would help tomorrow. Outside temperature was indicated at 79 degrees at 10 p.m. while I did the test.

Also, when I pull out the fault codes, I'm getting a B1234. I think that has something to do with the sun sensor.

The following page was some help in pulling my own diagnostics, in case other newbies run across this thread later:
http://continentalimports.com/ser_ic40142.html

So, a shot of refrigerant is in order? Other tips / ideas? Thanks again!

Cheers, John

This condition was more exagerated on my car. In fact, one side would have the heat on full eventually (the driver's side, in a US car) while the other side would be on full cold. I would "fix" the problem by turning the defrost on for a few minutes and then off, and I would get ice cold air from both sides. For a while.

Turned out to be the "duovalve" for the hot water flow to the heater core on the driver's side. New duovalve and the problem went away. One of the guys on the Diesel Forum actually posted instructions on removing and cleaning the valves to fix the problem.

Hope this helps, Jim

Start by charging the system. As indicated earlier, often this is caused by low charge.

also to test if it is low freon do the following:
turn both zones to LO and hit the ec button, measure temp, and if they are the same then freon is likely your issue, if the drivers is still warm then you definately have a control issue, may even be a leaking duo valve

Thanks, guys. I'm going to drop by a local shop for a system charge sometime later this week if I can. Might have them put the dye in too, in case I'm leaking somewhere. Then I'll test and drive and see what happens -- will report back once I've had time to get some freon in her.

Cheers, John

Looks like Carson357 may have hit the nail on the head. I popped by a local shop today to get the system charged, and it was showing proper pressure on the refrigerant lines. However, it behaved very badly for the tech -- the driver's side vents were blowing out HEAT, and the passenger side was cool.

So...where to now? I'll run some searches on "duovalve." Is this something I can fix on my own, or am I about to be facing a huge dealer bill? Thanks for any tips!

Cheers, John

Have the system evacuated & properly recharged to the correct amount (WEIGHT). guage readings is a very poor method of checking for correct charge!

Thanks, Doc -- I called the local shop back to inquire about having this done, and they were very defensive about their work -- and the charge for the 5-minute pressure check they did for me. Bunch of pricks...I'll take my business elsewhere. Before I do anything else, given the heat that came out today, I'm going to open up the duovalve and just see if anything is sticking in there. Once it's back together, if there's no change, I'll go back and have the refrigerant done properly. Ballpark on what that should cost?

Cheers, John

Proving the DUO valve bad is a SIMPLE task that takes less that 5 minutes.

Simply block off the heater supply line with needle nose pliers.. I have special hose type pliers that won't damage the hose. If you have a piece of rubber you can use it between the pliers & the heater hose.

Several of us have gone through this exact scenario. Here is an old thread, with some link to other sites with ways to check.

http://www.peachparts.com/shopforum/showthread.php?t=125161

In my case the duovalve was the problem and you can tell by running the diagnostics on this site:

http://www.continentalimports.com/ser_ic40142.html

My results were posted here:

http://www.peachparts.com/shopforum/showthread.php?t=108173

The net result is when the heater core temperature is at the engine coolant temperature and you have the A/C on, there is a problem that is entirely independent of the freon level or the A/C circuit efficacy. In this case the heater can overpower the A/C (which is as it should be since the outside air can be mighty cold and by the time it gets to you inside has to be warm). In my case the driver's side heater core temp was hot as hell and the passenger side, where the A/C was working, was at "ambient" or so.

With that set of symptoms the problem cannot be fixed with the freon being recharged. It is a bum valve letting engine coolant circulate through the heater core when the control system says "close" or "throttle" and the valve actuator opens the valve all the way.

There is a most excellent post on how to fix the duovalve, which I wish I had stumbled across before I paid to have mine fixe, by Parrot of Doom, but it is on another MB website:

http://forums.mercedesclub.org.uk/showthread.php?t=25909

You will have to register there too to read the instructions and view the excellent step by step photos that accompany the step by step process. It looks like a reasonable job to carried out by someone with reasonable skills. I will sure try it the next time my valve fails.

Hope this helps if the freon thing turns out not to be the answer. It wasn't for me.

Jim

I didn't see this post while I was researching the links for my post above. This would definitely tell you if the duovalve was the problem or not and best of all it is free.

Jim

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

if you do what i suggested, no need to pinch off or dissasemble anything, all can be done inside the car, when you do it a/c and heat are both off heater valve is completely closed since it is on LO, and a/c off since it is on ec, if you feel heat the valves are leaking pure and simple, if all is the same the freon is low.

turn both zones to LO and hit the ec button, measure temp, and if they are the same then freon is likely your issue, if the drivers is still warm then you definately have a control issue, may even be a leaking duo valve