hi i have a 78 280z,when i turn heat on it blows cold air.I can open the flap door behind blower motor(well on blower motor housing)and it turns hot.Could the heat control valve be stuck closed or bad.checked all vacuum hoses all connected.

 

I'm having this same issue. And I am stumped. I even replaced the heater control valve. When I accelerate all the air moves to the vents but won't blow hot air

 

77280zx while car is running and heat is on go to passenger side reach behind heater blower and push flap door and see if it heats up.

 

It doesn't

 

Check your heater vacuum hoses. They are on the right-hand side of the engine bay close to the cabin. You will see 1 hose coming from inside the firewall. Trace that hose to the cluster of hoses attached to the side of the engine bay. These hoses are prone to fail after a couple of years, so this is a common problem (mine are failed too). It's a easy fix, if you're careful. The failure will occure where the hoses end -- so look for a split in the hose near the end.

Let me know how it goes. Good luck.