III-74
Performance Inspection – Engine Running
The purpose of visual and electrical inspection is to detect obvious problems and assure
AC system function for an accurate performance inspection. If you do the performance
inspection first, you could be mislead. Problem areas discovered during the perfor
-
mance inspection can give you false clues or symptoms, and result in repair errors and
come-backs. The following performance inspection procedures are explained in more
detail below:
1. Inspect System Component Cycling and
Cab Temperature Levels
2. Check Clutch Cycling Under Load
3. Check Sight Glass
The performance inspection does not cover pressure and temperature sensitive safety
devices (cutout switches, fan control, Trinary etc.). Testing these devices requires the
use of the manifold gauge set for observation of internal system pressures during tests.
These are explained in
C
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.
Use the following procedures as a general rule in a performance inspection:
1. Inspect System Component Cycling and Cab
Temperature Levels
A. Turn On the Engine and Air Conditioner – Inspect for system compo-
nent cycling and cab temperature levels.
Note: System performance testing will be much faster if all doors
and windows in the cab are closed.
The cab air must cool down to thermostat control setting lev
-
els before system components will cycle on and off, indicating
correct function. This is called ¶stabilizing the system· and takes
about five minutes of operation. In very hot weather the system
may not cycle.
B. Check Thermometer Readings – In the cab you can use your thermom-
eter to measure air temperature at the vents. When the evaporator is easy to
reach with a thermometer probe without removing some of the dash or duct
work, use the probe to measure evaporator temperature. When the AC unit
is on and working correctly, you can see the thermometer dial needle move
down to about 32 degrees, then rise six to ten degrees and move back down
again. The movement up and down indicates that the cycling clutch and
thermostat, or orifice tube and accumulator pressure switch (to the clutch)
are functioning correctly. In systems with a non-cycling clutch, this move-
ment indicates correct function of the refrigerant metering device.
The needle movement is called “temperature swing.” When you can ad-
just the thermostat setting, the range of swing should change. For example,
from full cooling (cold) to moderate (between cold and warm), the swing
may change from 32-38 to 32-42 degrees.
Electrical System Inspection
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