Delphi’s Radial-4s may not
be modern high-tech, and they’re not known for ultra-quiet operation.
But after early teething pains, they proved to be reasonably durable.
Though they haven’t been
in OE production for years, many vehicles on the road have them, so
brand-new replacements are still being manufactured.
And some Radial-4s have
been failing on 1994-95 Chevy/GMC Suburban with rear air, and more
than one replacement per vehicle. It isn’t the compressor. The problem
is that the compressor is being hit with liquid refrigerant, which
when it’s pumped out, is taking oil with it. The root cause is a
defective rear expansion valve.
Symptom: the compressor
will get very noisy under low-cooling loads as a result. However,
there are lots of other possible causes, so here again, is one example
of why you need an accurate refrigerant charge in the system (we have
another, later on).
There’s a straightforward
way to check the rear TXV on these models, with a pyrometer on the
suction line, (accessible behind the right rear wheel). Push back the
rubber protective sleeve and clamp or tape the pyrometer probe to the
suction line. Run the engine at idle, system in recirc, rear blower
off and front blower on low-medium speed. After 15-20 minutes the
pyrometer should read 32-34 degrees F., which indicates the expansion
valve is working properly. If the temperature reading is 46 degrees F.
or higher, the expansion valve is stuck open and allowing refrigerant
flood back. Yes, we know this is time consuming, but did you just want
to guess?
The fix: the better choice
in an OE rear expansion valve has a straight capillary (Parker
Hannifin Part No.52459601), and if it’s what you get, check the
attachment (should be with two claws) and when you install, wrap with
insulation and tape.
However, you may be
offered a superseding part, one with a coiled end, for which a
specific clamp is provided. However, the aftermarket grapevine says
the accuracy of the sensing may not be nearly as good. Even unwinding
it carefully may not provide an installation with as good and reliable
sensing over the long term, according to those familiar with the
parts. In addition, the clamp provided with the coiled-type would be
unsuitable.
For the moment, back to
the subject of refrigerant charge accuracy. If you don’t have an
accurate charge
in
the system, those pyrometer temperature readings are meaningless.
However, we’ve got a variation on this problem that really is
something else: a total of six (count ‘emsix) compressors on a ’95
Suburban. It raises additional issues, including that rear TXV.
When the Suburban Radial-4 in one case repeat-failed,
the shop didn’t check service bulletins. It thought all it needed was
to solvent-flush the system and then install a (new) replacement.
However, debris had blown back into the suction line and of course, it
hit the new compressor and caused still another failure.
Compressors Nos. 3, then 4 and 5 were installed,
apparently more with a sense of desperation than a willingness to step
back and think. A look at the suction manifold following the 5th
failure showed that no screen had been installed, and a look into the
suction port of one of the failed compressors showed a chunk of debris
wedged in.
Backing up a bit: with No. 4 had finally came a new
rear TXV, one that had the same superheat rating but with the coiled
capillary tube, and it was installed, but it wasn’t the answer.
Flushing also wasn’t doing the job on this front-and
rear air system, and after the fifth compressor failed, hard thinking
and looking turned up a debris-loaded screen on the rear TXV.
At this point, highly-experienced outside advice
insisted on more than solvent-flushing and rear TXV screen
replacement.
Although the coiled-capillary rear TXV may not have
been the sole cause of another repeat failure, there was suspicion at
least it had contributed. Installing the OE type with the straight
capillary would likely produce an installation that senses more
accurately.
The orifice tube (which had metal debris) was replaced,
a suction side screen also was installed and an
in-line filter was put in the liquid line. And yes, an
OE rear TXV with the straight capillary was located and installed.
Finally, the funerals were over. No. 6 lives! The 1994-95 Suburban are
not a high-volume line of SUVs, but if you encounter the problem and
need that type of OE TXV with the straight capillary for those
Suburban, Global Air of Hollywood, FL (954-922-0053) says it carries a
supply.
