Service; Economizer Assembly; Electronic Expansion Valve (Exv); Flooded Cooler Main Exv Control - Carrier AQUAFORCE 30XA080-500 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

Table 47B — 5K Thermistor Temperature (°C) vs Resistance/Voltage
TEMP RESISTANCE
(C) (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
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

SERVICE

Economizer Assembly —
30XA090-500 units has an economizer assembly. The
30XA080,082 units do not have an economizer and have one
main electronic expansion valve. The 30XA080,082 units are
controlled the same way as units with a separate economizer
assembly. See Fig. 46.
Electronic Expansion Valve (EXV) —
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 3690 (main) or 2785 (economizer) steps.
FLOODED COOLER MAIN EXV CONTROL —
circuit has a thermistor located in the discharge end of the com-
pressor (DGT) and another one located in the compressor mo-
tor cavity (SGT). Each circuit also has discharge and suction
TEMP RESISTANCE
(C)
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
Each circuit on the
See Fig. 47
Each
74
(Ohms)
7,855
7,499
7,161
6,840
6,536
6,246
5,971
5,710
5,461
5,225
5,000
4,786
4,583
4,389
4,204
4,028
3,861
3,701
3,549
3,404
3,266
3,134
3,008
2,888
2,773
2,663
2,559
2,459
2,363
2,272
2,184
2,101
2,021
1,944
1,871
1,801
1,734
1,670
1,609
1,550
1,493
1,439
1,387
1,337
1,290
1,244
1,200
pressure transducer. Discharge and suction pressure as mea-
sured by the transducers are converted to saturated tempera-
tures. The main control logic for the EXV uses discharge su-
perheat to control the position of the EXV. The difference be-
tween the temperature of the discharge gas and the saturated
discharge temperature is the superheat. The EXV module con-
trols the position of the electronic expansion valve stepper mo-
tor to maintain the discharge superheat set point.
The EXV control logic has several overrides, which are also
used to control the position of the EXV.
• Approach between SST (Saturated Suction Temperature)
and LWT
• Maximum Operating Pressure (MOP)
Approach — If the approach (pinch), which is the difference
between leaving fluid temperature and saturated suction tem-
perature, is equal to or less than the pinch set point then the
EXV will not open any further even though discharge super-
heat set point is not met. Pinch set point is calculated using
suction superheat, discharge superheat and pinch offset. Pinch
offset is used to adjust calculated pinch set point do to accuracy
of transducers and thermistors.
MOP — The EXV is also used to limit cooler saturated suction
temperature to 62 F (16.6 C). This makes it possible for the
chiller to start at higher cooler fluid temperatures without over-
loading the compressor. This is commonly referred to as MOP
(maximum operating pressure). If the SST is equal to or greater
than the MOP set point then the MBB will try to control the
EXV position to maintain the MOP set point.
TEMP RESISTANCE
(C) (Ohms)
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
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