I am not thinking of bypassing the vacuum bottle just the two magnet valves.

why would vacuum be shut electrically to the heater control?

I'm not sure why Nissan did that. It makes sense for the FICD magnet valve since it raises the idle when the AC is on but not for the other one.

Well I will do some experimenting, it should be a simple matter to find out. I will post what I find

Ok so I ran a strait line from the vacuum canister to the heater controls looks like my heat works now, cool it never worked since I've owned my car but there are some other issues with the air ducting I will need to examin. time to read up in the FSM....

Grant,

Nothing gets shut off with the heater or a/c is on. When you turn on the a/c, the microswitch activates the solenoid to split off some vacuum to bump up the idle, ad the rest goes to the mode switch. See if you can locate "fast frog's" vacuum diagram.

The first magnet valve doesn't make much sense. That valve is broken on my car, with apparently no replacement available, and I had this exact conversation some time ago. I couldn't figure out any real need for it, and neither could anyone else. My system works fine without it.

That said, I do believe the accumulator (football thing) and the check valve are probably necessary. Your engine vacuum goes up and down. If you were to climb a long, steep hill at WOT, for instance, your vacuum would be quite low, and without the football and check valve, all of your actuated heater doors and whatnot would relax. That certainly wouldn't be the end of the world, but it would make more sense functionally to have the football and check valve to give you a very high vacuum approximately on a continuous basis.

My vacuum canister has been totally removed. the vacuum line from the engine goes straight into the heater control, and everything works fine.

My vacuum canister has been totally removed. the vacuum line from the engine goes straight into the heater control, and everything works fine.

Sounds about right but is there not a check valve that would prevent a vacuum leak if something were amiss?

Mine is missing if there is.