Section 6
Service
6-5
LIQUID LINE THERMISTOR
Function
The liquid line thermistor senses the refrigeration
system liquid line temperature. This is used in
conjunction with the control board to determine the
length of the freeze and harvest cycles.
Specifications
10,000 Ohms
±
2% at 25
°
C (77
°
F)
CAUTION
Use only Manitowoc thermistors.
CHECK PROCEDURE
Thermistors generally fail because of moisture or
physical damage. Manitowoc liquid line thermistors
are encased in a specially designed, moisture-sealed
aluminum block. This eliminates physical damage
and moisture concerns.
Verify that the thermistor resistance is accurate and
corresponding to the high and low temperature
ranges.
1.
Disconnect the thermistor at the control board.
Connect the ohmmeter to the isolated thermistor
wire leads.
2.
Using a temperature meter capable of taking
readings on curved copper lines, attach the
temperature meter-sensing device to the liquid
line next to the thermistor aluminum block.
Important
Do not simply “insert” the sensing device under the
insulation. It must be attached to and reading the
actual temperature of the copper liquid line.
3.
With the ice machine running, verify that the
temperature of the discharge line (step 2)
corresponds to the thermistor resistance reading
(step 1) as stated in the temperature/resistant
chart.
Important
If the thermistor would fail closed, the light on the
control board will flash rapidly.
If the thermistor would fail open, the light on the
control board will flash slowly.
Temperature/Resistance Chart
As the temperature rises at the thermistor block, the
resistance drops.
Important
If the ohmmeter reads “OL,” check the scale setting
on the meter before assuming the thermistor is bad.
Temperature of Thermistor
Resistance
°°°°
C
°°°°
F
K Ohms (x 1000)
15.6
°
- 21.1
°
60
°
- 70
°
15.31 - 11.88
21.1
°
- 26.7
°
70
°
- 80
°
11.88 - 9.29
26.7
°
- 32.2
°
80
°
- 90
°
9.29 - 7.33
32.2
°
- 37.8
°
90
°
- 100
°
7.33 - 5.82
37.8
°
- 43.3
°
100
°
- 110
°
5.82 - 4.66
43.3
°
- 48.9
°
110
°
- 120
°
4.66 - 3.75
48.9
°
- 54.4
°
120
°
- 130
°
3.75 - 3.05
54.4
°
- 60.0
°
130
°
- 140
°
3.05 - 2.49
60.0
°
- 65.6
°
140
°
- 150
°
2.49 - 2.04
65.6
°
- 71.1
°
150
°
- 160
°
2.04 - 1.68
71.1
°
- 76.7
°
160
°
- 170
°
1.68 - 1.40
76.7
°
- 82.2
°
170
°
- 180
°
1.40 - 1.17
82.2
°
- 87.8
°
180
°
- 190
°
1.17 - 0.98
87.8
°
- 93.3
°
190
°
- 200
°
0.98 - 0.82
93.3
°
- 98.9
°
200
°
- 210
°
0.82 - 0.70
100
°
212
°
0.73 - 0.62
(boiling water bath)
104.4
°
- 110.0
°
220
°
- 230
°
0.59 - 0.51
110.0
°
- 115.6
°
230
°
- 240
°
0.51 - 0.43
115.6
°
- 121.1
°
240
°
- 250
°
0.43 - 0.37
121.1
°
- 126.7
°
250
°
- 260
°
0.37 - 0.33
