Just what the title says. The only time it every stops blowing is when the fan is shut off. Is there an actuator that runs the center and side vents for when the defrost and heater is going? Otherwise it just keeps pooring out to much cold air for the heater to keep up with. Thanks in advance

Well, since nobody knows what you're driving (year, etc) then you'll continue to feel cold air.

Yes, there are cables and vacuum lines that open and close doors to direct airflow to the correct places. It's hard to say much beyond that. As Dave said, we need a year.

hey guys..sorry, forgot bout that . its a 76' with factory air. again...sorry bout forgettin that lil detail

I'm pretty sure the '76 has a mode door that diverts air flow either to the heater core or to the AC's evaporator coil. (At least that's how my '78 is configured.) On the 78, the door is controlled by vacuum lines. I'm pretty sure the vacuum lines on my '78 were original, and they were cracked/broken in a few places. None of my vacuum operated parts were functioning. I strung new lines and restored my system to full functionality. It wasn't a fun job, but it wasn't that hard either.

If you don't have one, you should get a copy of the Nissan factory service manual for your car. You can order one used on Amazon (my recommendation), or you can download a free electronic copy online. I'm sure someone else will have a useful link for you, as well as information more specific to the '76.

Good luck!

Yep, you have cracked vacuum hoses. Cut a small piece off, take it to an auto parts store and buy enough to do the whole underhood and interior. I think it takes about 12' if I remember right. Until you replace them, reach up under the dash allthe way to the firewall with your right hand while in the driver's seat and you will feel the vacuum diaphram. There is a rod on the bottom that you can push up with your finger. Once up, the air will divert to the floor or defrost depending on HVAC lever position.