Driver abhors a lack of vacuum

Q: My ventilation air has begun blowing only out of the defroster on my Ranger pickup. Advice?

A: Based on your symptom, it sounds like the Ranger uses engine vacuum to operate the air delivery doors, as opposed to a growing number of vehicles that use electric servos.

A slender plastic hose is routed from the intake manifold to a check valve, then to a vacuum reservoir (a metal or plastic container), and continues into the Ranger's cab, ending at the dashboard's ventilation control panel. Behind the panel is a vacuum switch, which directs vacuum through additional hoses to operate servos at the vents.

A vacuum hose could be separated, kinked, collapsed, or perhaps the vacuum reservoir has become damaged and is leaking. Take a look under the hood on the passenger side for this hose. Detach at various sections to feel for vacuum with your fingertip, engine idling, in the hose and at the reservoir. If vacuum is present, visually follow the hose prior to entering the cab, checking for kinks or damage there.

Diagnosis beyond this point will likely require disassembly of the instrument panel. Dropping the glove box may be worthwhile.

E-mail Brad Bergholdt at under-the-hood@juno.com.