The root cause of the repeat-failures of the DENSO
compressors on Tahoe/Yukon/Suburban is oil starvation, but it’s a
problem unrelated to the Suburban. In certain operating conditions,
the oil accumulates in the rear evaporator (typically front A/C off,
rear on with lower blower).
It’s a known problem, particularly on 2000-2001 models,
and the fix also is known: covered in a bulletin (No. 01- 01-39-002B,
issued 12/03/01) but the part numbers are outdated. However, it
explains how to change all the plumbing to improve oil circulation
(basically a rear line bypasses the accumulator, going directly to the
compressor).
We’re not going to repeat the procedure here, as you
should have access to service bulletins, but there are some important
things you should understand about this fix specifically, and General
Motors service procedures for compressor failures.
For this fix, a lot of new parts are required – just
flushing and replacing the condenser, accumulator, orifice tube won’t
produce a lasting repair. Now let’s talk flushing:
As we’ve noted earlier, unlike Ford, GM never validated
a solvent flush. Why? It’s a difference in service procedure
philosophy among the A/C service engineering teams and the service
equipment suppliers with whom they work, plus the debris from failures
it was seeing.
GM decided it wanted to flush only to remove dirty oil,
such as from desiccant failure and a small amount of metal. It could
do that with liquid R-134a, adapters and a special port on its new
recycling machine, which dealers already had, rather than add a new
machine and flushing agent. GM had used liquid-line filters for some
time, was satisfied with them, and trusted suction screens as
finishing touches And as part of factory fixes, it changes
accumulators and even condensers where indicated.
An important note: even if you flush with liquid
refrigerant and aren’t trying to get out a lot of debris, you still
have to remove the orifice tube and expansion valve (rear system in
this case), the accumulator and any lines with mufflers. GM has an
adapter kit (No. 45268) to bridge the joints, although shops also have
made their own, such as by taking failed expansion valves and drilling
through them. But the shop-made adapters won’t have the filter the GM
kit includes.
The GM approach is to back-flush front and rear systems
separately, front first, blocking one while flushing the other. And
with the needed refrigerant recovery, you can see why it’s
time-consuming, as noted earlier in this report. Further, many
recovery machines are not designed for refrigerant flushing.
That explains why a lot of shops try to do the job with
a gun and solvent flush, or even something like the Ford approved
machine and flush. GM can’t tell you if that will work, and Ford
certainly can’t tell you what its equipment does on GM vehicles. We
can tell you that an independent shop that doesn’t do liquid
refrigerant flushing is unlikely to be successful trying to fix this
problem with a solvent flush and minimized replacement of parts.
Because a refrigerant flush is time-consuming, GM even
requires dealers to get specific approval for it. And the fl at-rate
time on the factory fix is about six hours (figure a lot more if you
don’t do this job regularly, have to order parts, etc.), and that
doesn’t include the flushing operation. With everything, this job
surely can run over a three-day period. It can get very pricey if the
vehicle is out of warranty, explaining why independent shops look for
safe shortcuts and fewer parts replacements.
Sorry, we understand the issue, but the shortcuts have
led to repeat compressor failures, and a new or even quality reman
compressor is not pocket change.
GM only approves liquid refrigerant flushing if there
was a catastrophic failure of the compressor or some other cause of
oil contamination, desiccant bag failure, evidence of contaminated
refrigerant (GM dealers have identifiers, and every A/C specialist
should too) or a gross overcharge of oil. It’s backflush for most of
these, but there also is a forward flush procedure (using a check
valve that has been removed for backflush).
Forward flush is just for contaminated refrigerant oil
(with engine oil maybe?) and/or contaminated refrigerant.
Otherwise, GM relies on such parts replacements as
expansion valve or orifice tube, accumulator and certain hoses (and
the condenser if necessary), plus installing the liquid line filter.
GM also recommends a suction side screen in the compressor manifold.
DENSO doesn’t approve suction screens, but it also doesn’t approve
trace dye, and GM not only uses trace dye on the assembly line, but
specifies adding it during this factory fix. We suspect that dealers
will be installing the screen, and cautious independent shops should
too.
