I have a 1995 Chevy Blazer, the A/C blows out the defroster
vent only. I have read that the most likely cause is a leaky
or loose vacuum hose. Where would these vacuum hoses
When the Defroster is on, AC airflow and heater airflow are
both directed to the defroster vent. This is because the
AC air is very dry and defrosting works faster.
Under normal (non-defrost) conditions, heat and AC airflow
are directed to the dash vents or to the floor vents by means
of Flapper valves in the ducts under the dash. Each Flapper
is operated by a vacuum-powered Actuator.
Vacuum is provided by a hose from the engine to the climate
control Selector. The Selector distributes the vacuum through
other vacuum hoses to the Flapper Actuators to direct airflow.
Where there is airflow but it is not coming from the proper
vents, it could be the result of (most probable first):
1.) A Flapper is stuck in one position by rust or distortion.
2.) A vacuum line from the Selector to an Actuator is leaking or
3.) The link from an Actuator to a Flapper is broken or disconnected.
4.) The vacuum line from engine to Selector is leaking or disconnected.
5.) The vacuum distribution section of the Selector is bad.
6.) An Actuator is defective.
Sorry, this does not answer your original question as to where
the vacuum lines are located. You will just have to get upside
down under the dash with a flashlight and root around to find
them. You can then also wiggle and free any stuck flappers.
John E. Ardans Bothell Washington
It is probably leaking under the hood. Look for a vacuum line from the
engine running toward the firewall. Also, turn off the radio, put the fan on
low, and listen for a hissing inside the car while running. They usually
come off under the hood after some underhood work was
done(tune-up,driveability). But if you just had some interior work done, I
would start there. If you cant find the line, You can pull the ac control
out and check for vacuum on the black & grey hose going to it. That comes
straight from the engine. If that is OK , I would find the leak at the
conrol head or lines leaving it.
There is a round ball about 4-5" in diameter attached to the hood with
vacuum hoses connected. One was loose and hanging between the engine and
firewall. But I can't find where it connects. Getting closer, am I on the
right track here?
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