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Table 39B — 5K Thermistor Temperature (°C) vs Resistance
SERVICE
Economizer Assembly —
Each circuit on
30XW175,200,350,400 units has an economizer assembly. The
30XW150,325 units do not have an economizer and have one
main electronic expansion valve. The 30XW150,325 units are
controlled the same way as units with a separate economizer
assembly. See Fig. 42.
Electronic Expansion Valve (EXV) — See Fig. 43
for a cutaway view of the EXV. High-pressure liquid refriger-
ant enters valve through the top. As refrigerant passes through
the orifice, pressure drops and refrigerant changes to a 2-phase
condition (liquid and vapor). The electronic expansion valve
operates through an electronically controlled activation of a
stepper motor. The stepper motor stays in position unless pow-
er pulses initiate the two discrete sets of motor stator windings
for rotation in either direction. The direction depends on the
phase relationship of the power pulses.
The motor directly operates the spindle, which has rotating
movements that are transformed into linear motion by the
transmission in the cage assembly. The valve cone is a V-port
type which includes a positive shut-off when closed.
The large number of steps and long stroke results in very ac-
curate control of the refrigerant flow. The stepper motor has ei-
ther 4260 (main) or 2785 (economizer) steps.
MAIN EXV CONTROL — Each circuit has a thermistor lo-
cated in a well in the discharge line of the compressor (DGT)
and another one located in the compressor motor cavity (SGT).
Each circuit also has discharge and suction pressure transducer.
Discharge and suction pressure as measured by the transducers
are converted to saturated temperatures. The main control logic
for the EXV uses discharge superheat to control the position of
the EXV. The difference between the temperature of the
discharge gas and the saturated discharge temperature is the
superheat. The EXV module controls the position of the elec-
tronic expansion valve stepper motor to maintain the discharge
superheat set point.
TEMP
(C)
RESISTANCE
(Ohms)
3 14,026
4 13,342
5 12,696
6 12,085
7 11,506
8 10,959
9 10,441
10 9,949
11 9,485
12 9,044
13 8,627
14 8,231
15 7,855
16 7,499
17 7,161
18 6,840
19 6,536
20 6,246
21 5,971
22 5,710
23 5,461
24 5,225
25 5,000
26 4,786
27 4,583
28 4,389
29 4,204
30 4,028
31 3,861
32 3,701
33 3,549
34 3,404
35 3,266
36 3,134
37 3,008
TEMP
(C)
RESISTANCE
(Ohms)
38 2,888
39 2,773
40 2,663
41 2,559
42 2,459
43 2,363
44 2,272
45 2,184
46 2,101
47 2,021
48 1,944
49 1,871
50 1,801
51 1,734
52 1,670
53 1,609
54 1,550
55 1,493
56 1,439
57 1,387
58 1,337
59 1,290
60 1,244
61 1,200
62 1,158
63 1,118
64 1,079
65 1,041
66 1,006
67 971
68 938
69 906
70 876
71 836
72 805
TEMP
(C)
RESISTANCE
(Ohms)
–32 100,260
–31 94,165
–30 88,480
–29 83,170
–28 78,125
–27 73,580
–26 69,250
–25 65,205
–24 61,420
–23 57,875
–22 54,555
–21 51,450
–20 48,536
–19 45,807
–18 43,247
–17 40,845
–16 38,592
–15 38,476
–14 34,489
–13 32,621
–12 30,866
–11 29,216
–10 27,633
–9 26,202
–8 24,827
–7 23,532
–6 22,313
–5 21,163
–4 20,079
–3 19,058
–2 18,094
–1 17,184
0 16,325
1 15,515
2 14,749
TEMP
(C)
RESISTANCE
(Ohms)
73 775
74 747
75 719
76 693
77 669
78 645
79 623
80 602
81 583
82 564
83 547
84 531
85 516
86 502
87 489
88 477
89 466
90 456
91 446
92 436
93 427
94 419
95 410
96 402
97 393
98 385
99 376
100 367
101 357
102 346
103 335
104 324
105 312
106 299
107 285
6" MINIMUM
CLEARANCE FOR
THERMISTOR
REMOVAL
1.188 in.
2.315 in.
1/4-18 NPT
Fig. 40 — Dual Leaving Water Thermistor Well
(00PPG000008000A)
a30-4080
Fig. 41 — Typical Remote Space Temperature
Sensor (33ZCT55SPT) Wiring
7
8
TB6
SEN
SEN
SENSOR
a30-4081
O-RING
BRASS NUT 3/8 - 24 FOR
ASSEMBLY ON BRASS WELL
Fig. 39 — 5K Thermistor
(30RB660036 Thermistor Kit)
a30-4079