Thermistor Failure - U-Line U-2218WCS-00A User Manual & Service Manual

USER GUIDE
SAFETY • INSTALLATION & INTEGRATION • OPERATING INSTRUCTIONS • MAINTENANCE • SERVICE
Thermistors
Thermistors are used for various temperature readings.
Thermistors provide reliable temperature readings using a
resistance which varies based on surrounding
temperatures. If a faulty thermistor is suspected it may
be tested using an accurate ohmmeter.

THERMISTOR FAILURE

Zone Thermistors
If the zone thermistor in the unit fails the unit will continue
to cool in a back up mode to preserve the integrity of the
contents. The unit will cycle on for five minutes, then shut
down for forty five minutes. The process will repeat until
the problem is corrected. All other functions of the unit
will continue to operate normally.
Evaporator Thermistors
If an evaporator thermistor fails the unit will rely on a
preset defrost timer during defrost cycles. The unit will
otherwise operate normally. Evaporator thermistor errors
are recorded in service mode "Error Log."
Ambient Thermistor
The ambient thermistor is mainly used for diagnostics. If
the thermistor fails, the unit will operate normally.
This unit has three thermistors. Thermistor one is located
along the right hand side wall. It is used to maintain the
operating temperature within the unit.
Thermistor two is located on the back of the evaporator. It
is used for defrost purposes.
Thermistor three is located by the condenser and is used
mainly for diagnostics.
All three of the thermistors in the unit are identical. If a
thermistor is suspected of being defective it can be
OHMed out. In an ice water bath the thermistor should
OHM out at 16.1k OHMS +/-5%.
Thermistor connections must be kept clean. A thermistor
connection that has become corroded can cause
resistance values from the thermistor to change as they
pass through a dirty connection to the board.
It is for that reason that we apply die electric grease to all
of our thermistor connections. Die electric grease will help
to keep thermistor connections clean and dry.
If you change a thermistor in the unit please re-apply die
electric grease to the connection. If you encounter a dirty
thermistor connection, you should replace the thermistor
and the thermistor harness.
Thermistor Resistance Data
Temp (F) Temp (C)
-40
-31
-22
-13
-4
5
14
23
32
41
50
59
68
77
86
95
104
113
122
131
140
149
158
167
176
* (=/-5%)
56
Nominal Resistance
(OHMS)*
-40 169157
-35 121795
-30 88766
-25 65333
-20 48614
-15 36503
-10 27681
-5 21166
0 16330
5 12696
10 9951
15 7855
20 6246
25 5000
30 4029
35 3266
40 2665
45 2186
50 1803
55 1495
60 1247
65 1044
70 879
75 743
80 631
Thermistor 1