a/c venting to windshield

My 96 boneville a/c blows cold but operating in defrost mode.I replace the 2 way check valve near the dryer,still have the same problem it does not want to switch to main vent.Any opinions, ideas
thak you!
Zero,

If you have the auto ac it could be a vacume line off of the hvac i had the same problem it under the dash and you may have to remove the dash but worth a look at

I'll try that!,
Also I will trace the vacum line to see if is has a leak or is damage.
thanks.
zero

be careful when you pull on it its fragel and might break off the way mine did it hard to get to under the dash

My 93 had same problem. Found the vacume hose on engine side of firewall had been pulled off while changing plugs. Plugged it back in and it worked.