‘92 245; AC works and gets really cold, but the vents only blow in the correct position they’re set to for like 10 minutes. Then they’re uncontrollable, and it’s a guessing game as to which vents are blowing air.

I checked the black and white check valve off the intake manifold, and the vacuum connectors at either end of it were dry rotted and cracked. I blew into it and it only blows one way. Replaced the bad looking connectors, and reinstalled it - no change.

Where do I start from here? What are the more common issues on 240s with the HVAC vacuum system? I haven’t put my vacuum tester to the check valve on the manifold yet, I guess there is a chance it is not holding vacuum long enough; it does look original, or if not, very old...