a/c direction problems=--

98 base lumina, 3.1 about 275,000 miles on it.

Problem =--a/c often defaults an blows cold thur the defroster area.

My mobile mechanic is honest and highly skilled, drives a lumina and has been to Chevy factory training in Lumina days.
I bought a new vacuum resevoir ball. He tried that idea. He tested several vacuum lines and did various things all with no success. He thinks it may have something to do with one or two solinoids under the dash , behind the glove compartment.

Any idea,s will be appreciated.
It is very toasty in south Louisiana nowadays.

Very simple to test the system with a hand held vacuum pump....if the actuators are vac operated...

"Defrost" is the default position for the HVAC system, because that way you're sure to have a frost-free, clear windshield.

He replaced the "ball" reservoir, but did he ever test the vacuum tubing to see if it holds vacuum? I've had multiple failures in the vacuum tubing (brittle crap) that had to be spliced with rubber vacuum hose. (This is on a '92 and 93 Lumina. I suspect but don't know for sure that the newer ones use vacuum-operated air doors rather than electronic actuators.)

thank you to Tech II
and
thank you to Schurkey.

a quicky solution=
I placed a small fan on the dash blowing into my face on defrost mode.
It ain,t perfect, but it,ll do.
Occasionally try a/c or max and if it works leave it like that .