C6.2.24/0215-0515/E 19
4.3.3 Low-pressure control
IMPORTANT!
Loss of system charge! Bearing malfunction! A low-pressure control is
highly recommended for loss of charge protection. Do not bridge or by-pass
the low-pressure cut out.
Even though these compressors require a discharge temperature sensor, loss of system charge
etc. will result in overheating and recycling of the motor protector. Prolonged operation in this
manner could result in oil pump-out and eventual bearing failure.
A minimum cut-out setting of 0.3 bar(g) is required for the ZFD compressors using R404A. For
ZBD compressors, the low-pressure cut-out should be set as high as possible. The normal
minimum is 2.6 bar(g).
The low-pressure cut-out should have a manual reset feature for the highest level of syst em
protection.
4.4 Discharge temperature protection
Internal discharge temperatures can reach unacceptable values under some extreme operating
conditions (such as operation outside the approved application limits, improper control operation
or loss of refrigerant injection charge). This could cause compressor damage.
Discharge gas temperature protection is required for any application with Copeland brand
compressors in order to guarantee positive compressor protection. This protection must not be
used as an operating envelope controller but as a safety device.
Compressors ZBD21K* & ZBD29K*: These compressors have no internal temperature
protection. Therefore they are supplied with a discharge temperature thermostat.
Compressors ZBD30K* to ZBD57K* and ZFD13KVE to ZFD25KVE: These compressors are
equipped with a discharge temperature sensor (NTC thermistor) that is embedded in the top cap
of the compressor. The output of the NTC thermistor is used in the protection module of the
Digital Scroll controller. The resistance curve for the NTC thermistor is provided in Table 8
hereunder.
Table 8: Digital Scroll thermistor temperature / resistance v alues
-40 2889.60 75 12.73
-35 2087.22 80 10.79
-30 1522.20 85 9.20
-25 1121.44 90 7.87
-20 834.72 95 6.77
-15 627.28 100 5.85
-10 475.74 105 5.09
-5 363.99 110 4.45
0 280.82 115 3.87
5 218.41 120 3.35
10 171.17 125 2.92
15 135.14 130 2.58
20 107.44 135 2.28
25 86.00 140 2.02
30 69.28 145 1.80
35 56.16 150 1.59
40 45.81 155 1.39
45 37.58 160 1.25
50 30.99 165 1.12
55 25.68 170 1.01
60 21.40 175 0.92
65 17.91 180 0.83
70 15.07
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