78
OMM 1008-1
Maintenance
!
DANGER
Wait 10 minutes after compressor shutdown before opening any compressor access panel.
The DC link capacitors store enough energy to cause electrocution.
Pressure/Temperature Chart
R-134a Temperature Pressure Chart
°F
PSIG
°F
PSIG
°F
PSIG
°F
PSIG
6
9.7
46
41.1
86
97.0
126
187.3
8
10.8
48
43.2
88
100.6
128
192.9
10
12.0
50
45.4
90
104.3
130
198.7
12
13.2
52
47.7
92
108.1
132
204.5
14
14.4
54
50.0
94
112.0
134
210.5
16
15.7
56
52.4
96
115.9
136
216.6
18
17.1
58
54.9
98
120.0
138
222.8
20
18.4
60
57.4
100
124.1
140
229.2
22
19.9
62
60.0
102
128.4
142
235.6
24
21.3
64
62.7
104
132.7
144
242.2
26
22.9
66
65.4
106
137.2
146
249.0
28
24.5
68
68.2
108
141.7
148
255.8
30
26.1
70
71.1
110
146.3
150
262.8
32
27.8
72
74.0
112
151.1
152
270.0
34
29.5
74
77.1
114
155.9
154
277.3
36
31.3
76
80.2
116
160.9
156
284.7
38
33.1
78
83.4
118
166.0
158
292.2
40
35.0
80
86.7
120
171.1
160
299.9
42
37.0
82
90.0
122
176.4
162
307.8
44
39.0
84
93.5
124
181.8
164
315.8
Routine Maintenance
Refrigerant Cycle
Maintenance of the refrigerant cycle includes maintaining a log of the operating conditions and
checking that the unit has the proper refrigerant charge.
At every inspection, the suction, and discharge pressures should be noted and recorded, as well as
condenser and chiller water temperatures.
The suction line temperature at the compressor should be taken at least once a month. Subtracting
the saturated temperature equivalent of the suction pressure from this will give the suction
superheat. Extreme changes in subcooling and/or superheat over a period of time will indicate
losses of refrigerant or possible deterioration or malfunction of the expansion valve. The
evaporator operates at 0º to 1º F (0.5º C) of superheat through most of the load range. The
refrigerant used for compressor cooling dumps at the compressor suction, where the suction
temperature sensor is located. This results in a warming of the suction gas and superheat readings
of 4º to 5º F (2º to 3º C).
The discharge superheat should be between 16º and 18º F (9º to 10º C) and remains fairly constant
through most of the load range.
Liquid subcooling is in the range of 8º to 9º F (4.5º to 5.0º C).
