77
The microprocessor has been programmed to check the op-
eration of the thermistors. If the measured temperature is out-
side the range of –40 to 245 F (–40 to 118.3 C) and 168,250 to
203.75 ohms (outdoor-air temperature, supply-air temperature,
saturated condensing temperature, suction gas temperature, and
return-air temperature only), it will be treated as a sensor fail-
ure and a diagnostic code will be displayed. It is also possible
to check the operation of the thermistors using the test function.
To check the thermistors:
1. Use the temperature subfunction of the status function
(
) to determine if the thermistors are reading
correctly.
2. Check the thermistor calibration at a known tempera-
ture by measuring actual resistance and comparing the
value measured with the values listed in the thermistor
tables (Tables 59 and 60).
3. Make sure that the thermistor leads are connected to
the proper pin terminals at the PSIO1 and PSIO2
terminal strip J7 on the processor boards, and that the
thermistors are properly located in the refrigerant
circuit.
If a thermistor has failed or the wire is damaged, replace the
complete assembly. Do not attempt to splice the wires or repair
the assembly.
Table 59 — Thermistor Resistance vs Temperature Values for Thermistors T1-T7 (5 K at 25 C Resistors)
TEMP (F)
RESISTANCE
(Ohms)
–25
98010
–20
82627
–15
69790
–10
59081
–5
50143
0
42678
5
36435
10
31201
15
26804
20
23096
25
19960
30
17297
35
15027
36
14614
37
14214
38
13833
39
13449
40
13084
41
12730
42
12387
43
12053
44
11730
45
11416
46
11111
47
10816
48
10529
49
10250
50
9979
51
9717
52
9461
53
9213
54
8973
55
8739
56
8511
57
8291
58
8076
59
7868
60
7665
61
7468
62
7277
63
7091
64
6911
65
6735
66
6564
67
6399
68
6237
69
6081
70
5929
71
5781
72
5637
73
5497
TEMP (F)
RESISTANCE
(Ohms)
–25
98010
–20
82627
–15
69790
–10
59081
–5
50143
0
42678
5
36435
10
31201
15
26804
20
23096
25
19960
30
17297
35
15027
36
14614
37
14214
38
13833
39
13449
40
13084
41
12730
42
12387
43
12053
44
11730
45
11416
46
11111
47
10816
48
10529
49
10250
50
9979
51
9717
52
9461
53
9213
54
8973
55
8739
56
8511
57
8291
58
8076
59
7868
60
7665
61
7468
62
7277
63
7091
64
6911
65
6735
66
6564
67
6399
68
6237
69
6081
70
5929
71
5781
72
5637
73
5497
TEMP(F)
RESISTANCE
(Ohms)
74
5361
75
5229
76
5101
77
4976
78
4855
79
4737
80
4622
81
4511
82
4403
83
4298
84
4195
85
4096
86
4000
87
3906
88
3814
89
3726
90
3640
91
3556
92
3474
93
3395
94
3318
95
3243
96
3170
97
3099
98
3031
99
2964
100
2898
101
2835
102
2774
103
2713
104
2655
105
2598
106
2542
107
2488
108
2436
109
2385
110
2335
111
2286
112
2238
113
2192
114
2147
115
2103
116
2060
117
2018
118
1977
119
1937
120
1898
121
1860
122
1822
123
1786
124
1750
TEMP(F)
RESISTANCE
(Ohms)
125
1715
126
1680
127
1647
128
1614
129
1582
130
1550
131
1519
132
1489
133
1459
134
1430
135
1401
136
1373
137
1345
138
1318
139
1291
140
1265
141
1239
142
1214
143
1189
144
1165
145
1141
146
1118
147
1095
148
1072
149
1050
150
1028
151
1007
152
986
153
965
154
945
155
925
156
906
157
887
158
868
159
850
160
832
161
815
162
798
163
782
164
765
165
749
166
734
167
719
168
705
169
690
170
677
171
663
172
650
173
638
174
626
175
614
TEMP
(F)
RESISTANCE
(Ohms)
176
602
177
591
178
581
179
570
180
560
181
551
182
542
183
533
184
524
185
516
186
508
187
501
188
494
189
487
190
480
191
473
192
467
193
461
194
456
195
450
196
444
197
439
198
434
199
429
200
424
201
419
202
415
203
410
204
405
205
401
206
396
207
391
208
386
209
382
210
377
211
372
212
366
213
361
214
356
215
350
216
344
217
338
218
332
219
325
220
318
221
311
222
304
223
297
224
289
225
282
