MACS Monthly Newsletter - 2021 - APR4

Mike Bailey

* FLUSH GUN AND SOLVENT...to remove debris on the high side of
the system?
* CLOSED SYSTEM FLUSHING... should I use liquid refrigerant and
my recovery machine to remove all remaining oil contaminated
with compressor grindings from components I will not or can not
replace?
* LIQUID FILTER... can I add a filter on the liquid side to capture
debris that cannot be removed from components being re-used?
* SUCTION FILTER... can I add a filter to the suction side to protect
the new compressor I am installing?
* FILTER/DRYER CHANGE OUT... Food for thought...on a larger
more expensive system, it may be beneficial to complete repairs
and run the system with the new filter/dryer for a period. The new
filter/dryer is replaced again as a preventive measure, after it has
had a chance to capture any remaining debris from the system.
The best technicians repairing larger expensive systems do this to
ensure the system and compressor does not fail due to remaining
debris.

Figure 9: The control valve is mounted in the rear head of
the compressor and can be mechanical in design or electronic (Figure 15). Another " clue " to identifying a variable
displacement compressor is the casting bulge to accommodate the valve.
help technicians identify a variable displacement compressor.
This is important. Gauge readings will only make sense under high heatload conditions. If a technician does not " set the vehicle up " properly, diagnosis can be incorrect. When this happens, the vehicle may leave the shop
cooling nicely with a happy customer at the wheel. Give it a bit of time and
there is that vehicle again. The customer, shop owner and the technician are
now unhappy.
" Comebacks " cost money, and customers
Keep in mind, comebacks cost money. Even worse, the vehicle may leave
the shop the second or third time with the same problem.
Shop owners, counter staff and technicians turn into the nicest people
when something goes wrong! We are great folks already, but to keep a customer happy we really pour it on. Think back and this may sound familiar.
The customer brings the vehicle back. He or she may decide to wait. Or
Not. If they wait, a technician is more than likely going to be pulled off a paying job to address the comeback. Cost #1.
Paying work is outside waiting to come in, but the comeback takes priority.
Cost #2.
The technician assigned to the comeback is going to diagnose the entire
system again. If the " best tech " is assigned to the comeback, shop revenue
drops again. Either way, the technician is probably being paid to fix the comeback. Cost #3.
If the same component, say the compressor is diagnosed again, our supplier will probably supply the part at no charge provided we can document
the initial replacement unit was correctly installed. Though the supplier may
have a program to cover labor on the warranty replacement, the supplier
warranty labor rate may be nowhere close to your door rate. Cost #4.
Warrantying the job, we are probably not inclined to recoup the cost of
incidentals like O-rings, refrigeration oil, hardware, shop supplies or refrigerant. Cost #5.
In the event of a misdiagnosis and another component is found faulty, well,
this is where we fall all over ourselves to keep the customer happy. The full
door rate probably will not be charged for labor, if even charged at all. Parts
may be invoiced at cost or just given away to get the job out the door. Cost #6.
Did someone drive the customer home and pick them up? Did the shop put
them into a courtesy vehicle? Cost #7.
And so on. Air conditioning service is expensive for both the customer and
the repair shop.
I get calls from shops and technicians all day for many different issues.

Mike Bailey

Variable levels of confusion
Have you ever found yourself checking pressures of an A/C system, and
something just looks " off " ?
The system may cool perfectly but wow; is that high-side pressure gauge
reading low!
It may not be cooling properly but the low-side pressure gauge reads
properly.
Before heading over to the diagnostic dart board or firing the parts cannon, take a moment to do a bit of research. Check service info or even get an
eye on the compressor.
It is sometimes challenging to find the information you need, or it may not
even be noted in the service manual, but in order to test ANY system properly,
technicians need to determine if the compressor is FIXED or VARIABLE displacement. Figures 8 and 9 provide a few design characteristics which can

Figure 8: A few characteristics of variable-displacement
compressors: A) The " nose " of a variable displacement
compressor is typically rounded or of reduced diameter
compared to the rest of the compressor body. This " taper " can be accomplished because the pistons face the
rear. B) The control valve, located in the rear head, can
be mechanical (shown) or electronic with a plug or wires.
C) Many have a plug in the main body to allow for oil
balancing during service.

April 2021

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MACS Monthly Newsletter - 2021

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