I have a '96 E320 sedan and a question about my AC. The left side (drivers) air vents are 15-30! degrees F warmer than the right side (passenger) vents. Here its between 80-90F outside. Otherwise, the system is well charged and the car seems to be running fine. Ideas? Thank you.

 

If you have one, check the duo-valve. A pair of solenoids which control water flow to the heater box. Common issue when temperatures are out of balance (left vs right). There is a youtube video on testing/cleaning.

 

I clamped off the valve on the "radiator" side but could test no difference. The valve did get pretty hot and clicked a lot...would the clamping have cut the hot water supply? As I said, the hoses in and out still were very hot.
Thanks

 

RichardM98 was right on the money when my 99 E320 did the same thing.
I followed the youtube video and solved the problem, and don't be put off
if some " boob " posts " Did you turn the A/c on?
Marioa

 

Here's my experience to date.
As my MB mechanic estimated the services needed for my 96 E320 at about $4k, I decided it was upgrade time and bought a beautiful 2009 C65-E350. (Its got everything but a backup camera - go figure, so that project is ahead.) Then I drove my E320 one last time and realized it works great except for the AC, so decided to dig in myself. With a Blue Book of ~$2000, what did I have to loose? Its worth more than that to me!
My MB mechanic had said the evaporator was leaking as we saw dye around the transmission where the water drains. He wanted $1500+ to pull the evaporator out of the dash and replace it. Leak-wise, I was re-filling every 2 months. Also, he said the system normally blows warmer on the driver side and doubted the valve was an issue. I bought another on Ebay for $25 in the meantime...(looks new enough...)
I read a bunch of posts and decided first to add some AC system sealant and see what if. I got Interdynamics - A/C Leak Sealer Part # MRL3 because it says it seals metal parts too. Two months out, I'm still holding a charge! But I'm ahead of myself...
I decided to dig into the AC system too. As it cost me about $100 every time I went to the mechanic to recharge every 2 months (using vacuum, refill by weight + oil) I bought a set of gauges from Harbor Freight ($55), a vacuum for $20, and a 30 lb can of R134a refrigerant from Sam's Club ($80).
I put the gauges on the car in 90 degree Texas and the high side read off the scale (500+)! Low looked too low (20 as opposed to ~45). I decided to add refrigerant by the gauge technique and promptly over-filled it as evidenced by the compressor chunking. So I evacuated properly to 40+ and for some reason the high side is now at about 200 instead of 250 (or the 500!)! But it works great - maybe overfilling blew out some blockage.
Got lucky - I didn't crater my compressor, and 2 months in it still blows fine. It still is warmer on the drivers side so when I get time I will try swapping the valve.
If I need to add refrigerant again, I will start adding PAG oil too.
To be continued...