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1985 Nissan 300ZX A/C Mode Switch

My 1985 Nissan 300ZX’s air condition blows cold, but it will only blow at the windshield, and the far left and far right vents. Doesn’t matter which mode I push. The car doesn’t cool down to well in Arizona with most of my cold air meeting the hot windshield. It doesn’t help that I have a dash cover that sorta blocks the defrost vents, though only barely. What I want to know is what to replace to fix the mode selection. Is there a relay, a switch somewhere, or is it the dash unit itself? I don’t think its hoses, but is that possible? If someone can point me in the right direction as to what parts I might need, that would be great.

I tried looking it up on google, and browsing eBay for A/C parts, and seeing if any sounded like this was their function, but no luck.

Airflow direction is controlled by flaps, or doors, inside the HVAC system. The doors may be vacuum or electrically operated, not sure on your car.

The problem could be in the actuators that more the doors, or the door could be stuck, or it could be in the controls. If the system is vacuum operated it could, indeed, be a leaking vacuum hose.

If this were my car I’d take it to a shop specializing in automotive HVAC systems. They are the experts.

Why guess? You could throw parts at it and not fix it. Take it to an expert.

Another option is to obtain a service manual and try to diagnose the problem by following the flow chart in the manual.