My wife's 1988 S-15 Jimmy has a vacuum leak in the heater/air conditioner
control head (behind the levers which control temperature and air flow).
Two competent shops AND a not-quite-so-competent dealer have been unable to
fix this, because all of the replacement parts have been defective, right
out of the box. Can someone suggest where to find a control head which
doesn't leak, how to fix a leaking one, or how to find someone (in Colorado
or perhaps Nebraska) who truly knows how to fix one?
These control heads are a wonder of vacuum engineering...when they work.
Two plastic discs rotate against each other, directing vacuum through an
intricate maze of passages, thus moving vacuum-powered actuators which
control the air flow. In many cases, one of the plastic discs seems to be
ever so slightly warped, thus "letting the vacuum out." :-)
I too have the same problem, Can hear bad leaking behind dash,
depending on my speed and where i position the levers changes the pitch
and amount of vacuum leak I can hear. Just out of curiosity, I know a
vacuum leak in the engine bay can cause poor performance. Would this
leak effect my trucks performance?
It could. If a leak is small enough, the vacuum pump can maintain vacuum
in the rest of the system. But it doesn't take much of a leak to impair
the whole, interconnected vacuum system. In an earlier episode
of our vacuum leak saga, repairing a vacuum leak in the heater controls
also fixed problems with rough idling, stalling, and poor performance.
I do have a bit of an update: we took the Jimmy to an air conditioning
specialist shop. Just in the process of diagnosis, they reinstalled the
control head and fixed 60% of the problem. That's pretty clear proof
that in addition to defective parts, both earlier shops AND the dealer
were underskilled, to put it nicely. They say that the rest of the
problem is a combination of defective parts and debris from botched
repair attempts. That's pretty clear proof that in addition to defective
parts, both earlier shops AND the dealer were underskilled, to put it
nicely. Now the bad news: the specialty shop said they needed to order a
tool before they could complete the repair, and that they'd call us when
it came in. That was a month ago. I suspect the job is difficult enough
that they just don't want the business--or the future business that we
planned to bring them if they did a good job. :-(
Still looking for a competent mechanic,
Paul in Colorado Springs
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