First time user!

I have a 1994 C280 with a continuous air flow problem. When the problem first appeared in 1997, air flow through center vents would drastically reduced when accelerating and flowed through defog vents instead. Air flow would return to normal after stopped accelerating approx 3 seconds. Front pushbutton control switches had no effect on direction of air flow.

I brought in for service, they changed the vacuum controller unit. Problem was gone.

4 years later, the problem repeated and is now worsen (8/2001), air flow through side vents only. Previous problem repeated. One way to temporarily fix the problem is to set the air temperature to "LO".

Is there any easy way to locate the problem and fix it ourselves without going through the dealer? Is the vacuum unit defective again, or the cracked vacuum hoses would contribute to this problem?

Many thanks for your advice.