Emerson Liebert PEX Series, Руководство пользователя

Страница: 94 / 109

Chapter 7 System Operation And Maintenance 89
Manual reset switch
Automatic reset switch
Upflow electric reheat
Manual reset switch
Automatic reset switch
Downflow electric reheat
Figure 7-4 Upflow electric reheat and downflow electric reheat
7.6 Cooling System
Check the cooling system components once a month to make sure the system function is normal and that there are no
signs of wearing. Because the failure or damage of components is usually accompanied by corresponding faults,
regular check is a major means to prevent most system faults. The refrigerant pipes must be supported by properly set
brackets, and be laid away from the ceiling, floor or anywhere that vibrates. Check the refrigerant pipes and fixing
brackets every six months.
Each system has a sight glass to facilitate the observation of refrigerant flow and the system moisture content. When
the system moisture content is too high, the sight glass color will be changed. ‘Bubbles’ can indicate a shortage of
refrigerant subcooling.
When the cooling system is faulty, you can locate the fault by referring to certain parameters of system operation.
7.6.1 Suction Pressure
The compressor may stop when the suction pressure drops below the setpoint of the low pressure switch. On the
other hand, too high suction pressure will undermine the cooling effect of the refrigerant on the compressor motor,
leading to the damage of the compressor. The minimum (pressure switch action setpoint) and the maximum (design
operation value) suction pressures are listed in Table 7-1.
Table 7-1 Suction pressure
System Minimum pressure kPa (PSIG), R22 Maximum pressure kPa (PSIG), R22
Air-cooled (stepless fan speed controller) 138 (20) 620 (90)
Water-cooled 138 (20) 620 (90)
7.6.2 Discharge Pressure
The discharge pressure may change with the load or the condenser efficiency. When the discharge pressure rises to
the setpoint of the pressure switch, the high pressure switch will act to stop the compressor. See Table 7-2 for details.
Table 7-2 Discharge pressure
System design kPa (PSIG)
Air-cooled 1750 (251)
Water at 65°F ~ 75°F 1400 (203)
Water-cooled
Water at 85°F 1450 (210)
Maximum pressure 2275 (330)
High pressure switch action point 2760 (400)
7.6.3 Suction Superheat Degree
The thermal expansion valve (TXV) can regulate the suction superheat degree. Follow the following procedures to
determine the system suction superheat degree.
1. Measure the temperature of the suction pipe at the TXV sensing bulb.
2. Sample the compressor suction pressure at the schrader valve of the suction pipe.
3. Evaluate the pressure difference between the sensing bulb and schrader valve of the suction pipe.
Liebert.PEX2 Series Air Conditioner User Manual