HVAC only blows through defroster

[js18018]

Everything was fine until it wasn't. AC only blowing through defroster duct. Some residual cool air comes out of the dash vents. Checked typical vacuum lines to reservoir, all seems fine. Found the red vacuum line to the fuel regulator blown off and laying on the manifold. Thought I found the problem but did not understand why it was off. Reinstalled the line but that did not fix the problem. Is it possible that there's a problem with the check valve and does anyone know where it's located? Has anyone had this happen to them? I can struggle without the AC but it also affects the heater as well and cold winter weather is coming. The selector doesn't change anything. I've just been down the road with the blend door replacement. I have ordered a smoke generator but it hasn't arrived yet and it's screaming hot outside so not real enthused about working outside but I do have to fix it. Any help would be appreciated. Just as an aside as anyone ever found a problem with the reservoir itself? This seems to have happened with the vehicle just parked. It worked when I parked it there and when I started it afterward it didn't. Truly stumped

 

[lil_Blue_Ford]

Check valve is on the vacuum line between the intake and reservoir, it’s just a little disk shaped thing.

If it’s blowing just defrost, a vacuum issue is usually the problem. Smoke machine is your best bet in locating it.

 

[DeeRanger]

I had same issue on my 01 Ranger. It was damaged vacuum lines behind dashboard (caused by mice). Luckily they were able to repair by removing radio from dashboard for access to lines.