Vacuum actuated vent problems - a possible workaround

My vacuum controlled Vents were functioning at a level that they would only blow from the dash vents whenever I didn’t have the throttle more than 1/8th of the way down. I of course hate having to choose between AC and accelerating, And I also hate the idea of removing the entire dash from my car, so this evening I installed a 12v vacuum pump from Amazon into my car. Now my vents blow nonstop. It draws less than 1 amp, so For power I simply connected to the positive side of the coil, and ran ground to one of the screws on the coil bracket. The pump is zip tied to one of the AC lines next to the coil. The vacuum line from the vent system to the manifold ended up being the perfect length to straighten out and connect to the pump instead. I have a link to the pump I used below. I will update this thread if it stops working, or if I find any way to improve it.

Hopefully someone finds this information useful.

https://www.amazon.com/dp/B074W35XZK/ref=cm_sw_r_cp_api_i_GTOfFb2F166SF

Edit: car is a NA 1994 940.

Another option is to add a vacuum reservoir. SAAB came factory fitted with these on the C900 turbo cars. You also should have a check valve installed on this port to keep boost out of the vacuum system.

Do you have it just constantly running rather than cutting off when pressure drops low enough? I'm not sure it will last too long like that...

Also, which model of car did you do this on? My 240 has a reservoir already and replacing the check valve was enough to keep everything happy...

I dislike the vacuum-controlled vents, but this seems like it would work well.

More info here:

https://forums.turbobricks.com/showthread.php?p=5793953#post5793953

DET17 said:

Another option is to add a vacuum reservoir. SAAB came factory fitted with these on the C900 turbo cars. You also should have a check valve installed on this port to keep boost out of the vacuum system.

Click to expand...

But the reservoir would only help for a while. What I did will in theory keep the vents going indefinitely.

Khrrck said:

Do you have it just constantly running rather than cutting off when pressure drops low enough? I'm not sure it will last too long like that...

Also, which model of car did you do this on? My 240 has a reservoir already and replacing the check valve was enough to keep everything happy...

Click to expand...

No vacuum switch yet. I wasn’t sure the pump would work at all. I will look into getting one now.

The car is a 1994 NA 940

Replaced the check valve last year

I wonder why yours didn't work correctly?

My '82 244 Turbo's vacuum vents work fine; did you try to find and fix the problem before jumping to plan B?

Had the same issue on my '89 740T. The vacuum reservoir under the bumper has a little cap at the opposite end of the vacuum hose that was cracked. $3 later with a new cap from Advance Auto, my vents blow like crazy even under boost. That, along with a new check valve keeps my vacuum vents blowing where I want them to even hours after shutting the engine.