230 Auto Heating & Air Conditioning
own conclusion about the problem. In describing vehicle
problems, drivers have been known to use hand gestures,
body language, and even simulate noises they have heard.
While this can sometimes be fun to watch, keep in mind it is
a part of the diagnostic process. Many times, important clues
can be found simply by observing a driver’s physical actions
while describing a particular problem.
In many cases, the person bringing in the vehicle
has already formed an opinion as to what is wrong. These
opinions are a common occurrence, often based on poor
or incomplete understanding of vehicle operation, advice
from uninformed friends, or other failures to fully compre-
hend the problem. The best course is to listen closely to the
driver’s description of the symptoms. Some drivers will be
sensitive to even slight changes, and may be overreacting
to a normal condition. Never accept a driver’s or another
shop’s diagnosis until you can verify it.
Often, the owner is concerned about the cost of repairs.
Some will even downplay the symptoms, hoping for an inex-
pensive repair. Very few vehicle owners are unconcerned
about the cost of vehicle repairs and maintenance. Do not
give any type of uninformed estimate, even though you
may have a good idea of the problem. Giving an estimate
without diagnosis is a mistake made by many technicians.
This practice invites one of two things to occur; either the
recommended repair will not correct the problem or it will
frighten the driver, who may decide to take his or her vehicle
to another shop or not have the repair done at all. Explain
that the charge for diagnosing the problem is actually more
cost effective than paying for a service, which in many cases
may not fi x the problem. Before going on to the road test, be
sure you have a good idea of the driver’s complaint.
Road Testing
In the case of many HVAC problems, it is usually not
necessary to perform an extensive road test. However, in
some cases, performing a short road test is the fastest way
to confi rm a problem. Before beginning a road test, make
a few quick checks to ensure the vehicle can be safely
road tested. Walk around the vehicle’s exterior and make
a note of any damage that is present. Check each tire to
ensure they are infl ated properly and in good condition.
Also make sure that all safety-related equipment, such as
the turn signals and horn are working properly.
Warning: Do not road test a vehicle that is
not safe to drive. Low or no brake pedal,
tires with exposed steel or cloth cord, and
slipping transmissions are all examples of problems
that would render a vehicle unsafe.
Turn the steering wheel and make sure the steering sys-
tem does not have excessive play. Depress the brake pedal
to ensure the brake system has at least a minimal pedal.
Also make sure the vehicle has enough fuel to conduct a
road test. Do not adjust anything in the passenger compart-
ment, such as mirror, seat, and tilt steering wheel position,
other than what is absolutely necessary. If the radio is on,
turn it off so that you can listen for unusual noises.
Wear your seat belt at all times during the road test. Try to
duplicate the exact conditions under which the driver says the
problem occurs. Unfortunately, duplicating some conditions
is not always possible. Always try to road test the vehicle with
the owner. This will ensure you are both talking about the
same problem, and will save valuable diagnostic time.
Drive slowly as you leave the service area to ensure that
no obvious mechanical problems exist that could further dam-
age the vehicle or cause personal injury. Make one or two
slow speed stops to verify the brakes work properly. Drive the
vehicle carefully and do not do anything that could be viewed
as abuse. Tire squealing takeoffs, speed shifts, fast cornering,
and speeding can all be interpreted as misuse of the vehicle.
While road testing, obey all traffi c rules, and do not
exceed the speed limit. It is especially important to keep
in mind that you are under no obligation to break any laws
while test driving a customer’s vehicle. Also be alert while
driving. It is easy to become so involved in diagnosing the
problem, that you forget to pay attention to the road or the
traffi c around you. If it is necessary to look for a problem or
monitor a scan tool’s readout while the vehicle is driven, get
someone (not the vehicle’s owner) to drive for you. Once
you have verifi ed the problem exists, proceed to Step 2.
Figure 15-2. A logical troubleshooting process will enable you
to quickly diagnose and repair refrigeration system and other
HVAC system problems.
Determine the exact problem 1
Check for obvious problems 2
3
Determine which component or
system is causing the problem
Eliminate the causes of the problem 4
5
Isolate and recheck the causes
of the problem
Correct the defect 6
Recheck system operation 7