Billyo

79 L82 defrost and heat blow air out. In A/C air blows out heat vent. Have vacuum to selector switch. Temp cable adjusted right. Only way to get air out vent is to move selector over until vacuum comes out port that doesn't have hose and put your finger over it. Problem is after you remove finger and move selector it stays in vent mode. You have to shut controls off and start over. Moved actuator on left by hand slowly up down but air didn't come out center vent. Is there another actuator that controls that. Thanks for any help.

DUB

The vacuum switch at the back of your controls is what CONTROLS ALL of the modes of where the air comes out. Replace the vacuum selector switch on your HVAC control assembly.

DEFROST and HEAT at the floors is the DEFAULT MODE that GM chose. SO...if you had NO vacuum to your HVAC control head.....the air would ALWAYS blow out the defrost and floor areas....and would NEVER change until you got vacuum to the switch...and if you did....the vacuum switch can be bad....and they DO go bad.

DUB

Billyo

Thanks DUB found the problem after getting vacuum diagram to do test from Willcox. The original plug to selector was gone. Someone put hoses on but number 2 port on selector was nothing. After blocking this port off it works great. This weekend will install A/C.