When debris is an issue,
you need filtration. Sure, there are accessible screens that can be
replaced or cleaned (orifice tube, perhaps expansion valve and/or
receiver-dryer).
Inspecting them usually
indicates how much debris got through the condenser.
Suction side “thimble”
screens don’t look very big, but their shape gives them a surprising
amount of surface area and they save a lot of compressors from debris
that had blown back into the suction side.
A nasty problem with
debris: it often doesn’t stay put unless it’s trapped in a filter or
screen. So a technician changes some parts, but not the condenser,
runs the system and soon encounters a failure from an apparent
restriction.
This time he replaces the
condenser, but debris already came out and plugged an orifice tube or
expansion valve, which previously was replaced. So the parts all may
be new, but because of the sequence of replacement, there’s still
debris in the system. Moral: the more complete the repair the first
time around after catastrophic failure, the better, and if a suction
screen and liquid line filter go with it, you’ve got some backup
protection.
Flushing (if done
correctly for the full system) should remove all the oil, so you have
to make a suitable adjustment when you replace the compressor,
condenser, etc. There isn’t a “standard” procedure. A replacement
compressor may come with no oil, a full charge or some amount in
between. Because one compressor goes into systems with different oil
capacities, the best bet:
Rremove as much oil as
possible from the new compressor (it takes time. Turn the shaft slowly
until you are at the point of very diminished returns).
Then add oil to each
component according to the manufacturer’s recommendations for new
parts. There’s surely some oil left in the compressor and what you add
may result in an ounce or two extra in the system, but it beats an
ounce or two short.
A far greater problem is
from just bolting on a compressor with a full oil charge when there
may be more than a full charge remaining in the system from the OE
charge and any additions during previous service.
If it’s the first
compressor failure, no indication of much debris, and the technician
decides not to flush components, he should remember to adjust the oil
level in the new compressor, referring to what he could drain from the
failed one. However, if that compressor has lasted a long time, he
should remember that one of the reasons that compressors repeat-fail
is because the system is loaded with oil. Perhaps previous shops kept
topping up a leaking system and added a few ounces of oil each time.
Then the technician
installs a new compressor with a full charge of oil and combined with
debris left in the system, encounters a repeat failure. He replaces
that compressor, maybe changes the accumulator or receiver-dryer and a
couple of hoses too, but the new compressor contains still another
full charge of oil. Yes, even if the compressor doesn’t hydro-lock,
there’s so much oil in the system that cooling is bad. Perhaps the
technician tries adding more refrigerant to improve cooling, and the
head pressures go up. Well, you can see where this is leading.
But before putting back
all those trim pieces that he had to take off to gain access, the
technician also should leak check with a premium electronic detector.
Loss of refrigerant causes a performance drop, and if a technician has
been focused on the compressor and sees pressures that are in the
low-normal range, he concludes the compressor failed again. As we’ve
pointed out in previous issues, loss of refrigerant that leads to poor
cooling may not produce big changes in system pressures. But it
reduces oil circulation (the refrigerant carries the oil, of course).
So when the compressor fails once more –although perhaps
not until next season – the technician is complaining to his parts
supplier about compressor quality.
