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).
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