Date registered: Feb 2015
Vehicle: 1998 C280; 1987 560SL
Location: Southeast USA
Mentioned: 3 Post(s)
Quoted: 79 Post(s)
All of the vacuum lines that I can get to through the glove box opening except the red/blue & red/white one holds vacuum. I can verify the fresh air vent flaps are opening (dark red), and I think I have the legroom flaps opening (red/yellow), although I cannot see them. The supply line (red/green) to the switchover valve holds vacuum, but the check valve at the supply is not holding the vacuum (on order). The vacuum storage cube holds vacuum, but it is useless because of the bad check valve.
My diagram shows that the red/white line is default open, and should close the defrost flaps when vacuum is applied at the switchover. It takes a little vacuum and then it leaks off. The red/blue line takes no vacuum, but should open the center vent and supply vacuum to the flap side of the defrost actuator (not sure why - possibly throttling the defrost flaps?). I think there is a tee close to the defrost actuator and the line goes on to the center vent actuator.
So from what I can gather my defrost actuator is leaking or the connectors are leaking (likely). I had to replace most of the rubber connectors in the glove box hole, because the rubber had stretched at the connections and was leaking. That may be the same thing with the defrost actuator, but I was not sure how to access it. If the connectors are leaking I may be able to change them. I need to take the instrument cluster out to change a light bulb, so I may do that next. The only other way would be thru the radio hole? I would hate to have to take out the dash, but I guess I could do it? It has some cracks that I could try to fix.....