1980 300SD 116 has 82 617 engine and transmission. The switchover valve has been bypassed since I have had the car. Reading the various threads about overboost results made me want to reconnect this system. I began by removing the valve to check its operation. This is what I found: when 12 volts is applied to the electrical terminals there is a straight thru path for air flow from the intake manifold to the ALDA. When 12 volts is removed from the terminals the pressure immediately goes to a low level and then slowly bleeds off to zero. -- The Intake Manifold Switch. -- I found that this is is a normally open switch. That is to say, with no pressure applied the switch is open. Applying a small amount of pressure will cause the switch to
close.-----If I understand the way the system is supposed to work,isn't the direct connection from intake to ALDA supposed to be the normal condition?
And isn't an overboost condition supposed to reduce the pressure that the ALDA sees to a lower value? --- If I assume that these assumptions are correct then it would seem that the actions of the two components would be opposing the desired results. That is to say, given the way the relay works, should not the manifold switch be normally closed and open on pressure?? One electrical terminal of the valve is connected to 12 volts on run or start.The other terminal of the valve is connected to the active terminal of the switch. The other terminal of the switch is of course, grounded. I checked the intake manifold switch from the parts car and find that it is also the normally open variety.-- My questions : Do I have the incorrect manifold switch/ Do I have the incorrect valve?/Do I have an incorrect understanding of the way the system works?---- Have not seen the answer to this in any of the threads. can someone give me a clue? Thanks in advance. Regards, Willie