All,
I have a 1971 Cutlass. It has A/C. I am posting because when I have the Defroster turned on, air does come out of the defrost vents, but not as strong as I would like. I also can feel air coming out of the bottom vents as well. I then changed the switch to Max A/C and I didn't feel any air coming out of the dash vents.

I think something is going on with my mode door, and I have the service manual, but it doesn't say how to troubleshoot that. So I was wondering if anyone out there know how to troubleshoot mode door operation. I know I can apply vacuum to that line and see what happens but it would be nice to know what is supposed to happen when I do so. Thanks.

 

Generally there should be 90% air out the defroster vents and 10% out the floor vents...so sheck that the little shorty flex tubes that connect your plenumn to the defroster inlets are intact and not frayed or ripped causing low pressure blasting onto your windshield max air opens that right-hand door for max cooling...if your vacuum hoses are original, then check the ends where they slip onto the nipple and see if you have split ends replace as necessary