Hello All. The winter here in Oregon is fast approaching and I find that the air will not change from the center exhaust to the defrost. Further the temp will not get warm. Here is what I have:

- 76 280z

- no leaks in the heater core

- plenty of coolant

- Original AC works...though doesn't seem as cold as last year (no biggie)

- Had replace the heater control valve with a rebuild from The ZMan (original was leaking)

When I turn on the air, it comes out the from. When I move the lever to Defrost, the air remains coming out the front. Moving the temp lever to Hot, the air remains coming out the front and does NOT warm up.

I see a couple of splits in some of the vacuum lines, which I replace out today. However, I thought the change in air flow was all mechanical.

Any thoughts on what it could be prior to tearing everything apart??

Thanks in advance.

If you have original AC, then some of the control is vacuum. I have a 76 with original AC also, and have had the same problem. The vacuum lines to and from the white bottle in the engine bay and the two "magnet valves" (solenoids) have to be intact and the valves themselves have to work. I've had the lines split and also had the round black flow control gismo that the hoses run through (on the magnet valve bracket) clog.

There are diagrams in the AC chapter of the FSM. But, I believe, defrost is controlled by both vacuum and mechanical (to close the doors to the foot area in the cabin). I have also lost Defrost because a piece of carpet got stuck in those doors by the feet. The AC/heat control system is almost as complicated as the EFI system.

There were definite splits on the vacuum lines going into the solenoids as well as to the white bottle. I am currently replacing the lines will give 'er a try in a few minutes.

It was vacuum. I replaced the three original vacuum lines going to the white canister and solenoids. Heater turns on, air transfers to the defrost, and air is nice and hot.

Thanks for the help.