WD Catalog 2018

895 / 1003

7-7 - -
Electrical System Inspection
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 performance inspection can give you false clues or
symptoms, and result in repair errors and come-backs. The following perfor-
mance 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 Chapter 8.
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 andAir Conditioner – Inspect for system
component 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 levels 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
thermometer to measure air temperature at the vents. When the
evaporator is easy to reach with a thermometer probe without re-
moving some of the dash or duct work, use the probe to measure
evaporator temperature. When the AC unit is on and working cor-
rectly, 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 movement indicates correct function of the refrigerant
metering device.
The needle movement is called “temperature swing.” When you
can adjust 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.