Hot & Cold Air At The Same Time C280
 

My "new" 1994 C280 ACC system blows hot air out the side vents and cold air out the center vents at the same time. The heat works great now, but if you try to get some AC it will blow cold air out the center vents but continue to blow hot out the side vents. Any thoughts as to the problem?

do a search for duovalve, i am having the same problem.

Is there any way to test the duovalve on the car?

Also, at times the "cool" air out the center vents will stop and start blowing hot air only.

OK, I went ahead and replaced the duovalve and it appears to have eliminated the heat and cool air at the same time problem. It does seem that the car is not cooling as well as it I would expect. For one thing the force of the air out the vents is not all that strong even at the highest fan setting. Any thought as to why the blower is not putting out a stronger air flow?

Blower motor regulator may be weak.
Also, your refrigerant may be low as well.

Thanks cudaspaz for your reply. Do you get access to the blower regulator on a 1994 C280 below the wiper assembly like in the W124? Also, where is the cabin air filter located in the same car?

To access the blower motor and pollen filter on the W202 C class you have to drop the underdash panel on the passenger side . Pollen filter is above a rectangular cover with two sliding catches, cover your carpet before you start as it can be filthy if it hasn't been changed for a while, should be changed at least every 2 years.
Geo.:)

Replaced the cabin air filter and the air flow is much stronger. An easy job and low cost item with great benefits.:)

I'm starting to have a similar problem also. Where is the duovalve? and how much does it cost to replace? thanks

The dual valve controls the hot water flow into the heater core. It cuts that flow off when you need AC and back on when you need heat. It is a simple do-it-yourself project to remove and install the replacement valve. The cost of the part is around $200 and it is located on the passenger side of the engine compartment under a cover near the windshield. It has one hose coming into the valve and two going out.

I have a 1989 300E with the exact same problem. Would my model have the same valve as mentioned?

Thanks

Your W124 will have a Mono Valve, but yes it is the same type of valve. In fact, you may be able to find a repair kit for your Mono Valve and not have to purchase the part new.

2000 c280 no heat or a/c
 

something went out on my c280 i get only vent air it seems no ac or heat ????can anyone tell me what it could be ,and it doesnt blow very hard even on high fan ... thanks:D

I am having the same problem on my 94 Benz E320, W124 but can not find this valve in engine compartment. Where is on the passenger side? Is there link show picture of this valve?