Buick Repair Questions? Ask a Mechanic for Answers ASAP
Hello, you would need to remove the climate control panel on the center of the dash and verify you have engine vacuum to the control panel when it defaults to the defrost position. If not you need to follow it back to the firewall and make sure the vacuum supply is intact. If you have vacuum to the control panel the the control panel would need to be replaced.
Do you need more help with this concern?