248 Auto Heating & Air Conditioning
Hidden defects are common, and may cause a vehicle
to return again and again with the same defective part. Do
not let the vehicle leave until you are reasonably sure the
observed defect is the real source of the problem. Some
hidden problems can be tricky, such as a high side seal
that checks out ok with the engine off but leaks at high
pressures, or a bad relay that ruins a series of HVAC control
modules. This is where good diagnostic skills and customer
feedback can be helpful.
Whenever you work on a refrigeration system, always
try to determine the real cause of a failure, even when the
problem appears to be simple.
Documentation of Repairs
Part of the follow-up process includes writing on the
repair order what the problem was, and what was done
to correct the problem. This is called documentation
and it is a vital part of the diagnostic process. Every
repair order line should have three things. These three
things are:
❑
What the driver’s complaint was.
❑
The cause of the complaint.
❑
What was done to correct the complaint.
This type of documentation not only allows the
driver to clearly see what was done to correct the vehi-
cle’s problem, it also supplies a good history of what
has been done, Figure 15-25. If the vehicle should come
back with a similar problem, it gives you or the tech-
nician working on the vehicle a place to start looking,
without having to repeat some of the steps you took to
fi nd the problem.
Remaining Calm
One of the hardest principles of diagnosis is to remain
calm. Mastering your own emotions is often the hardest
thing to do, especially if you meet with a series of dead
ends while looking for a problem or are having to deal
with an angry customer, but it is necessary. Nothing will
be accomplished by losing your composure. If you lose
your composure, you will waste valuable time and pos-
sibly upset the customer. If you have picked up a tendency
to overreact to situations, you must unlearn this behavior
and teach yourself to remain calm. Only a calm person can
think logically.
Summary
When troubleshooting any refrigeration system or
other HVAC system problem, always proceed logically.
The seven step troubleshooting process enables the tech-
nician to quickly locate and correct refrigeration system
problems.
The first step is to determine the exact problem.
This usually involves questioning the driver. A series of
questions is the best way to determine the exact prob-
lem. In Step 2 check for obvious problems, or problems
that can be easily tested. At this time attach gauges or a
charging station and check static pressure. Excessively
high or low pressures in the system indicate a problem.
The third step is to determine which refrigeration sys-
tem components or systems could cause the problem.
Do this by conducting a system performance test. In
Step 4 put together the information you gathered in the
first three steps. Begin by checking the components or
systems that are the most likely sources of the problem.
In Step 5 double check the cause of the problem deter-
mined in Step 4. In Step 6 correct the defect and in
Step 7 recheck system operation. Do this by conducting
another performance test. If necessary, repeat Steps 1
through 6 until Step 7 indicates the problem has been
fixed.
Locating leaks is one of the most common refrigera-
tion system diagnosis jobs. Oil on the refrigeration system
fi ttings, compressor shaft, or evaporator drain hole indi-
cates a leak. If an obvious leak cannot be found, use one of
the following leak testing methods. Before leak checking,
always make sure there is some pressure in the system.
Some technicians pressurize completely empty systems
with nitrogen. At one time the fl ame type leak detector was
widely used. Today, however, electronic leak detectors are
more common. They are more refrigerant sensitive than
fl ame leak detectors.
Another common leak detection method involves
injecting a dye into the refrigeration system and allowing it
to circulate. The dye will leak out with the refrigerant and
stain the components at the leak. A soap solution test can
be used to locate large leaks.