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 Use Table 4-1 or 4-2 to determine the right resistance to use to impersonate a
particular temperature. An abbreviated version, with resistor color codes is
presented in Table 4-3.
TABLE 4-3: Resistance and Color Codes for Typical High Limit Situations
10K Resistance
Temperature
3K Resistance
and Color Code
and Color Code
(F)
160
500 Ohms
1700 Ohms
Brown, Violet, Red
Green, Red
180
350 Ohms
1200 Ohms
Brown, Red, Red
Orange, Green, Black
Control Tester Method
A more accurate method of testing differential thermostats is with a special tester
designed for the purpose (Figure 4-4). Normally, these units have four leads or
terminals. These are connected to the collector and storage sensor terminals of the
control. The tester supplies a calibrated resistance to the two sensor inputs.
Most of the available testers supply a fixed resistance to the storage terminals, and
change the resistance supplied to the collector terminals. The numbers on the
tester dial usually refer to the temperature difference between the storage and
collector terminals.
As the tester dial is slowly turned to greater differentials, the resistance supplied to
the collector sensor terminals is lowered. At the "on" differential, the control should
turn on.
TROUBLESHOOTING
117
4.3 TROUBLESHOOTING OPERATIONS
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