My wife's e320 blows hot air on the driver's side when the A/C is turned on. I figured the most likely culprit is an open and stuck valve. I removed the electrical connector from the duovalve and it still blows hot. Passenger side blow cold with the A/C on.

Have i diagnosed the problem correctly? Or could there be more wrong, like a stuck vacuum element? Or something more major wrong with the climate control

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I'd suspect a stuck duovalve. You might try this...

With both sides set to cold, cycle the valve several times by disconnecting and connecting the valve rapidly. I had a stuck valve free up by doing this and has been working fine ever since.

If that doesn't fix it measure the valves coil resistance. Should be 30-50 ohms from center pin to each side. The valve's solenoid coil can open which requires a new valve.

If coils are good then measure voltage at the connector to see if there's 13 volts on each side. If so, then the valve is stuck and you may be able to dismantle and clean it.

If you see 13V only on one side then there may be climate control, wiring problems.

Before you go crazy chasing stuff around make sure the A/C system is fully charged!

IIRC a low charge will cause what you are experiencing.

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Probably just low on refrigerant, but it's easy enough to diagnose. Read through Steve Brotherton's article here: link, put the climate control in diag mode, and post up the values of items 1-10 from the display. While the car is running, and has been running for a few minutes, BTW. The numbers will tell whether you have a leaking duo-valve or not.

The first time I pulled the codes, these are the numbers. Key on engine off and had been off for several hours


1: 87
2: 80
3: 100
4: 98
5: 100
6: 100
7: 06
8: 85
9: 27
10: 0.0

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Unless Mercedes turns the heater on for the driver side, the A/C has a good charge, as the passenger side blew pretty cold.

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thanks,,, I'll try these today, as it's getting hot up here,,,

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Afraid the numbers are only useful with engine on while driving the car. Numbers 3 & 4 are the left & right heater core temperatures. With good numbers we can tell whether the duovalve is admitting hot coolant or not. It's the easiest way to diagnose a faulty duovalve.

It's well established that cold right hot left can result from low refrigerant in the 210 chassis: link other link

I did the connect/disconnect with a/c on coldest setting. I heard what sounded like both valves clicking.

Here are the numbers taken today
# Value Value
1st 2nd
1: 105 100
2: 98 96
3: 111 91
4: 100 73
5: 103 94
6: 182 188
7: 12 12
8: 116 120
9: 33 33
10: 2.0 2.0

Stuck duovalve?

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My money's definitely on low freon charge - had exactly the same model car with the exact same problem in my driveway last month.

DG

Thanks for the links Jcyuhn, interesting. Think I'll take my long nose vise grips and clamp the heater hose for a few.

Me thinks I'll be rebuilding a duo-heater valve.

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I don't think so. You're left heater core temperature (#3 - 91 degrees) is lower than the outside air temperature (#2 - 96 degrees). That would indicate the air coming out the lefthand side of the car is being cooled, but not very much.

Your refrigerant pressure & temp (#7 & 8) are low for such a warm day.

Both these point to low refrigerant charge. I don't see anything that looks like a leaking duovalve.

How can he have cold air on one side with a low refrigerant condition?

The 2nd values were obtained after idling for approx 2-3 minutes with A/C on Max Lo. I noticed, last time my wife had the air on, it was set at 67 or so and that might have added to the problem.

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