On my '99 E320, the climate cotrol blows so-so cool on the passenger side, but blows warm on the driver side, when set to LO or 14degree temperature. Which part am I looking at replacing? Thanks a Lot!

Do a search - sounds like your charge may be low...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Your low on refrigerant. You'll need to recharge it and look for leaks.

You have a really modern Mercedes, with selective heat by position in the car!! Perhaps you can sell that system to others?? (Just kidding) BC

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)

Wouldn't that be "zoned climate control?"

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Check your heater hot water control valve (duo-valve);solenoid valve which controls the flow to each side of the heating; when faulty it defaults to full flow, probably one side of yours is faulty therefore constant hot flow , to check disconnect power lead at duovalve then both sides should run hot no matter where temp.controls are set.
See here, http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1SL15BCKH1SL15C9I7&year=1998&make=MB&model=E-320-005&category=R&part=ACC+Mono+Valve.
Geo

Same thing happened to me when i first got mine, get a vac and recharge.

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With best regards

Al

I will take it to an AC Pro and have it evacuated then re-charged.

I forgot to mention: There is a hissing sound coming out of the AC system. Intermittent, but it's there most of the time. Does this fact change the situation
(and required repair action)?

It is unlikely that the "hiss" is a leak, since you still have some cold air. A leak that you can hear, would empty the system in minutes, if not seconds.

Most likely, the "hiss" is what real pro A/C techs ( I'm not one!) report as refrigerant hissing thru the TVX when there is a low charge situation. This hiss probably confirms that you need more refrigerant in the system so I'd continue with your plan.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

THANKS everyone, you've all been too kind, I will proceed with evac/re-charge and have an AC pro do it. Thanks for all the input!

And they all lived happily ever after.