citruspilot

Have been gone on a 4 day trip and when I got back yesterday I slipped into my "hot" car and fired her up. Turned the a/c on and the fan came on and was blowing just fine. As I waited for it to start to cool I opened the sunroof and rolled down the front windows..........

As I started to drive I reached up to feel what the temp of the air was and noticed that the air coming out of the "left side" of the center vent was warm and the air coming out of the "right side" of the center vent was cold?????? Then I felt the air coming out of the left side dash vent and it was warm too. But the right side dash vent was cold. It appears that some of the cold air is getting to the right side venting system but not to the left. The temp is cold on the right side and the fan blows hard out of both sides.

Anybody????

Jeff

lexrex

It's possible your left heater core is stuck on (duovalve). But much more likely, you're low on refrigerant. If you can hear a hissing sound coming from the center vents, it's low refrigerant. Get it recharged and inspected for a leak.

The reason for the temp difference right to left is this: The refrigerant flows from right to left through the evaporator core. The right side gets first dibs. What little refrigerant you have left in the system gets warmed up on the right before it makes it to the left side.

citruspilot

Thanks lexrex. I bought the car last year in Oct. It has had the compressor changed as it appears to be new. The cooling has never been a problem until yesterday. It has been making a hissing sound of late but goes away rather quickly. I'll have the freon checked............ No wait, I'll do it myself.........

Jeff

citruspilot

OK, so where is the "low side" pressure hook-up point? I see a port that resembles an a/c adaptor on the drivers side just inside of the engine compartment over by the left bank of cylinders. Is that it?

Somebody help me before I do something stupid!!

Jeff

ohlord

Read my tips just posted
it will show you where the problem is,if it is a stuck duovalve,it can sometimes be freed up by giving it a firm but not excessive tap with the end of a medium weight screwdriver.If that doesn't do the trick.Search for the thread on cleaning the duovalve to make it like new.The duovalve is located on the pass side engine compt. and looks like two identical small tin cans side by side.these valves stick at times and they are the ones that divert the heat side to side,and are most likely you trouble
ohlord

raymond g-

dassit!

raymond g-

duovalve...

stick towel underneath when removing...to catch spooze...and screws (!)

citruspilot

Raymond, thanks for the pics. However the ones you posted are a bit different than what I see. The valve I was reffering to is lower down the side of the compartment and is attached to a cannister that has a few lines metal and rubber lines coming out of it. I was thinking that might be gas because one of the rubber hoses goes up and underneath the plenum cover, like it would carry gas to the intake system....... Dont want to mess with that one until sure...........

I'll look again for the valve you show............is that a 320 depicted??

Jeff

raymond g-

cp -
sorry, muh bad. was rushing to graduation events. yes, mine was for E320.
let me dig to see if I have any E420-430s....

citruspilot

Hope you enjoyed your graduation..................

The valve I saw was the right one. I put just a bit over 1lb of freon in and the problem has been solved, for the most part. Now, if only I can find where the leak is...............

Jeff

finadv

How's the A/C there citruspilot? I'm having the same problem, i.e. cold right, warm left. I called my mechanic and he said he can almost guarantee that it's the evaporator core and that I'd have to go to the stealership to have it done. He said he could add freon with some dye and look for a leak, but he thought I'd be wasting my money. He said that at the stealership it would cost about $1,200. Any thoughts.

csumt76

pop open the left fog lamp opening in the underpanel, and take a peek at the a/c line going from the condenser up to the receiver/drier. Pretty popular for that line to leak at the joint of the rubber hose/hard line, you might even see some oil/dirt at the source. Check it out, but the evaporators leak as well.

Howellja

Def. do a dye test! I had a slimeball mechanic try to tell me the same thing about the evaporator because he couldnt find a leak initially, but after driving around for a week and going to a different mechanic for an opinion sure enough it was the hose behind the foglight from the condensor to the drier. P.S. I dont go to that crook/slimeball anymore.

finadv

Left fog lamp. Is that the driver's side?

I trust this mechanic. He told me he expected it was the evaporator and he couldn't do it. He suggested I go to the dealership.

Thanks for the suggestions!!

lexrex

The direct cause of cold right, warm left is low refrigerant, not a bad evaporator core.

Low refrigerant, of course, suggests a leak. Evaporator core leaks are actually pretty rare compared to all the other sources of leaks. Adding dye and looking for a leak is absolutely what you should be doing.

ohlord

The direct cause is most likely a stuck duovalve,give it a good tap with the handle of a screwdriver and see if that frees it up.Run the onboard diag. and punch the numbers into the program I posted a few days ago,from another link on the site.Still like the others have said start with the easy things before jumping at a major failure part.
ohlord

lexrex

We obviously disagree on which is more likely. But there's no need to guess on low refrigerant vs. stuck duovalve.

If sensor #5 (evap temp) is greater than ~45 degrees, it's low refrigerant.

If sensor #5 and sensor #4 (right temp) are less than ~45 degrees, and sensor #3 (left temp) is more than 20 degrees higher than #2 (outside temp), it's a stuck duovalve.

P.S. I wrote the program that you linked to a few days ago.

finadv

Thanks guys. Great info. Without it, I probably would have went to the stealership and I'm sure they would have replaced the evaporator core first.

What a great site full of knowlegdeable people willing to help. I'll post what I find out.

ohlord

Cool,
no argument,just thought that if he starts with the simple remedy,i.e. a wack with the screwdriver,he might free up a stuck valve and at least be on his way toward a solution.
As to your program,It is great and a must read.Even if you don't have a/c problems you will be a more knowledgeable MB mechanic.
Thanks again and my donation is on the way
ohlord
p.s.
again I think running the onboard diag program is the best place to start,and your site is the best place to find that info

citruspilot

finadv, sorry, have been away and didnt get to respond before now. My cars a/c is still working fine. After I put a can, 1 lb., of freon in its still blowing cold out of both vents and the hissing has stopped. That was about ten days ago.

The a/c compressor has been replaced on my car because it looks fairly new. But I dont know when. If they replaced anything else in the a/c system I dont know. I bought the car in Oct last year and this is the first problem I have had with the system. I guess I'll wait to see how long it takes for the hissing sound to come back. That will be the first sign of a leak. Then its the dye process from there.......

Hope this helps you.

Jeff

starbrite

Jeff...if a leak, it may be from a spot that is ambient temperature dependent
(ie expansion/contraction)
Was the air temp about the same when you last heard the hissing sound compared to now ?

finadv

Added some freon with dye last week. So far so good. Very cold. If it leaks out, I should be able to find the source of the leak with the dye. So it seems like it was freon and not a stuck duo valve. Right on Lexrex.

okc329

for having the evaporator core fail. This of course leads to refrigerant leaks.

When my evaporator core went bad, the dealer first refilled with refrigerant saying that he couldn't find leak. A/C worked fine for a month or so and then problem came back. Dealer thensaid bad evaporator and $3600 to repace it.
I got parts from Phil @ Fastlane and went to my independent who has a great MB tech. He had the car for 4-5 days but did a perfect job and the A/C still blows freezing cold. That was 3 years and $2500 ago. The job is labor intensive as the entire dash has to come out.

finadv

Well that's not too reassuring. Here's hoping this time it's different. I'll post any news.