77 Cutlass - A/C air stuck in "Bi-Level"

[Guest]

need help to diagnose this problem w/ my 77 Olds Cutlass Salon, 350 V8:<BR>Blower is putting out plenty of air but most of it is blowing out at floorboard vents. Adjusting switch on control panel from "Bi-Level" to "Normal" has no effect - it stays in "Bi-Level" mode all of the time.<BR>all help to troubleshoot problem is most appreciated.<BR>wendy<BR>wendydot@swbell.net

[rocketraider]

This usually indicates a vacuum supply problem. First- check the vacuum hoses underhood, both at the engine and at the vacuum storage ball on the RH fenderwell. After 25 years you may have a broken or dryrotted hose. GM was using hard plastic vacuum lines by 1977 with rubber connectors at valves and storage balls.<P>Next- the vacuum selector valve on the A/C control may be leaking enough to cause this. It's a simple enough repair and common enough that I'd bet the local GM dealer has a few on the shelf.<P>If these don't fix the problem, it will be a failed vacuum motor on the upper or lower mode door inside the heater case. This requires removing the heater case from inside the car to fix and the vacuum diaphrams may no longer be available.