This is the 86 740 N/A, happened a couple of days ago just got the car yesterday. The vent control lever is stuck on max A/C, when i picked up the car yesterday I thought i could hear an air (vacuum) leak in the dash area but don't hear anything now. Due to all of the rain yesterday the car ran poorly at first due to what I believe is a leak in the windshield seal which I have sealed up with silicone temporarily, I don't think the 2 events are related but mention it as something else going on at the same time. I checked around under the hood for any vacuum lines that appear to be off/leaking and found nothing but may have missed something. The heater control valve looks Ok as does the vacuum line going to it.

I pulled the kick panel off below the steering wheel but I'm not sure what I am looking for, Haynes is completely useless (as usual) and the BB page talks about plugging off the yellow line to the servo but I see 3 servos?? Should I drop the splash pan and inspect the vacuum tank?? If the leak was that big wouldn't the car run poorly, it's starting and running fine right now? On BB they talk about a vacuum line coming out of the firewall next to the heater hoses that goes in to a tee then to the intake manifold but I can't find it?? Some of the tips are for 760's with ACC and some for turbos which is adding to the confusion as they are setup different than an N/A.

OK found something (I'm typing this and going out to the garage and coming back as I go), the vacuum line that comes from the firewall just below the cowl on the drivers side goes down and tees is off. One side goes to the A/C compressor (I'll guess it's a solenoid, actuator of some sort?) the other end is hanging loose!!! Where does that end go, I can't see anything obvious, I'm guessing it must go to the intake manifold b/c it needs to get vacuum from somewhere right?? Ok I'm posting this now, I'll be hunting around for a port and checking for responses. Oh, Matt if you're reading this I REALLY need to get this car fixed and out of the garage as the Rottweiler is making my life miserable (nothing like working under pressure when you have no clue what you're doing).

Nothing vacuum should go to the A/C. If we are talking 760, you usually have the vac tank thing underneath with a line going to the intake and a line going to the cabin. The only other line is for the heater valve thingy on the firewall, which I just eliminate and block the vac line. Some 760s got a little electric vac motor for added time to mess with vents in boost or whatever. I should mention there is also a check valve somewhere in the mix between intake and vac tank/cabin vacuum supply that prevents you from losing vacuum at WOT in an N/A and in boost in a turbo (duh).


The vacuum on a 700T is something like this:
Small vac lines:
One line goes to the compressor bypass valve *caugh* engine bay clutter *caugh*
Two atop the throttle body are for the charcoal can *caugh dead weight *caugh*.
One goes to the fitting for the crankcase breather. I also eliminate this and just run one big line straight from the breather box to the intake hose...no more leaking/oil in the intake. I keep the small vac line on N/A cars though.
One is for the climate controls
One is used with the EGR if you have it...er...dead weight again in my case and quickly ripped out and thrown as far from the car as possible.
One goes from the side of the intake to the fuel pressure regulator.

Cross off the bypass valve for an N/A car.
Big vac lines:
Brake booster

It is really not too bad unless something is wrong with the vacuum switcher under the dash or one of the tiny lines is bad (very uncommon). If that happens, burn it to the ground and get a 240 with like 1/2 all that crap or less. Be thankful it isn't an 80s emissions japanese thing...those are a vac line disaster. I am glad those cars are basically all dead now.

Hey James, thanks for that, I'm going to go back and make those changes after i get this mess figured out. What is the vac line that comes out of the firewall on the drivers side (not close to the heater hoses) and goes down and tees off to the switch/solenoid thing on the back of the a/c compressor and then, in my case currently goes nowhere?? Shouldn't this loose end be connected to a vac source??

Also if the vent control lever is frozen on the max a/c position is this likely behind the dash or under the hood? This is on an 86 NA which I found out is different than our 89 NA and 90 ti so I couldn't cheat off the other cars.