Q. My ventilation air has
begun blowing only out of the defroster on my Ranger
pickup. I wondered if there’s some advice you may have
on this before I start checking fuses, etc. It doesn’t
have air conditioning, so having air blowing at me is a
good thing with the warm weather.
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 which use
electric servos. Vacuum (reduced pressure) occurs in the
engine’s intake manifold due to the pistons pumping
air, and the throttle being closed or near to it - much
of the time, causing a restriction. Several golf ball
sized servos, each containing a rubber diaphragm, pull
the air delivery doors to the desired position, and a
spring subsequently returns them.
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 ventilation control panel.
The check valve and reservoir help to maintain a
consistent vacuum level as the throttle is periodically
opened wide. Behind the control panel’s mode control
knob or lever is a vacuum switch, which directs vacuum
through additional hoses to the appropriate servos.
Defroster-only operation is typically caused by a
loss of vacuum to the control panel switch. The vacuum
hose could be separated from a fitting, 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. After unplugging the
section of hose leading from the reservoir to the cab,
feel for vacuum at the reservoir nipple (engine idling)
with the tip of your finger. If there’s no vacuum,
check again prior to the reservoir, and follow the hose
as necessary back to the engine. If vacuum is present,
visually follow the hose as far as it can be seen prior
to entering the cab, checking for kinks or damage.
Diagnosis beyond this point will likely require
disassembly of the instrument panel. It’s possible the
vacuum switch has failed and is leaking vacuum, or a
hose is kinked or collapsed. Dropping the glove box may
be worthwhile, providing a glimpse of some of what you’ll
want to check. Keep in mind the fingertip vacuum test is
quick, but a vacuum gauge (16-19 inches of vacuum at
engine idle) would be better.
Q. How often should I replace my antifreeze if I live
in a warm climate, where freezing isn’t going to
happen?
A. Even if freezing isn’t a concern, I’d still
drain and refill the cooling system with fresh 50/50
percent antifreeze/water every three to four years.
Electrolysis is the enemy, due to a variety of metals
being used in the engine, radiator and heater core. Old
coolant can contribute to erosion of some very expensive
and labor-intensive parts.
