58 Auto Heating & Air Conditioning
Schematics
Schematics are pictorial diagrams which show the
path of energy through a system. This energy can take the
form of electricity, vacuum, air pressure, or hydraulic pres-
sure, Figure 3-42. Schematics do not show an exact replica
of a system, but instead indicate the fl ow or process within
the system. Some schematics show the exact fl ow of a form
of energy while others show the general process of a par-
ticular system. Schematics are often included as part of the
service information, or may be supplied separately.
Tracing the fl ow through a schematic makes diagno-
sis easier by showing the exact path of electricity or other
form of energy. Each line represents a single wire in the
vehicle’s wiring harness. The schematic lines are labeled
with numbers to colors to correspond with a specifi c color,
or color and color stripe combination on the actual wires.
The path can be traced by carefully following the lines from
component to component. Always carefully note the color
designations of the wires and any stripes or bands to ensure
you are following the correct wire.
Troubleshooting Charts
Troubleshooting charts are summaries, or checklist
versions, of the troubleshooting information about a par-
ticular vehicle or system. Although the information is found
in a longer form elsewhere in the service information, the
troubleshooting chart allows the technician to quickly ref-
erence the problem, the possible cause, and the solution.
Figure 3-43 shows a typical troubleshooting fl owchart.
Some troubleshooting charts are arranged with the problem
on the left-hand side of the page, the possible cause in the
middle, and the corrective action on the right-hand side.
Technical Service Bulletins
Frequently, manufacturers issue technical service
bulletins (TSB), for newer vehicles to their dealership
personnel. These bulletins contain repair information that
is used to describe a new service procedure, correct an
unusual or frequently occurring problem, or update service
Figure 3-42. A common electrical schematic such as the one shown above is a road map for the electricity in a circuit. As part of the
job, the HVAC technician is often called on to interpret schematics. (General Motors)
M
Motor
Driver