Thetford NR740 - Manual (Page 7)

Refrigerator Service Manual 7 DC0040(K), DC0051(K), DE0040, DE0051, DE0240T, DE0251T,
DC0740(X), DE0740(X), DC0751(X), DE0751(X) Models
Troubleshooting - Procedure E
Verifying Thermistor Operation
To measure the resistance of the evaporator thermistor, com-
plete the following procedure.
Turn the temperature control to the "Off" position. 1.
Disconnect the 3-pole connector. Refer to Figure 7. 2.
Measure the resistance across the two pins. Refer to 3.
Figure 8.
Check the evaporator thermistor by measuring the tem-
4.
perature and resistance of the thermistor.
Refer to Table 1 for a listing of acceptable resistance
ranges.
NOTE: In general, 1.6K - 29KΩ = good thermistor.
∞Ω = defective thermistor. An open thermistor
will stop normal compressor operation. Replace
the defective thermistor.
Evaporator Thermistor Resistance
Thermistor Temperature
(°F) (°C)
Resistance Allowable
Resistance
Range
0 -18 9.7 K Ω 8.7 - 10.7 K Ω
10 -12 7.8 K Ω 7.0 - 8.6 K Ω
20 -7 6.4 K Ω 5.7 - 7.0 K Ω
30 -1 5.3 K Ω 4.8 - 5.7 K Ω
40 4 4.5 K Ω 4.0 - 4.9 K Ω
50 10 3.6 K Ω 3.2 - 4.0 K Ω
60 16 2.8 K Ω 2.5 - 3.1 K Ω
70 21 2.1 K Ω 1.9 - 2.3 K Ω
80 27 1.9 K Ω 1.7 - 2.0 K Ω
90 32 1.8 K Ω 1.6 - 1.9 K Ω
Table 1. Evaporator Thermistor Resistance
AR
T01955
Figure 8. Measure Resistance Across Pins
AR
T01954
Figure 7. Evaporator Thermistor Connection
(Inside Power Supply)