Liebert Mini-Mate2 MMD24E User Manual page 70

System Testing and Maintenance
Air-Cooled Condensing Units
Restricted airflow through the condensing unit coil will reduce the operating efficiency of the unit.
Additionally, it can result in high compressor head pressure and loss of cooling. Using compressed air
or commercial coil cleaner, clean the coil of all debris that will inhibit airflow. In winter, do not permit
snow to accumulate around the side or underneath the condenser. At the same time check for bent or
damaged coil fins and repair as necessary. Check all refrigerant lines and capillaries for vibration and
support as necessary. Carefully inspect all refrigerant lines for signs of oil leaks.
Coaxial Condensers (Water/Glycol-Cooled Condensing Units Only)
Each water or glycol-cooled module has a coaxial condenser consisting of an exterior steel tube and an
interior copper tube. If the water supply is clean, coaxial condensers do not normally require
maintenance or replacement. Should your system begin to operate at high head pressure with
reduced capacity and all other causes have been eliminated, the condenser may be obstructed or
fouled and should be cleaned or replaced.
Regulating Valves
The water regulating valve automatically regulate the amount of fluid necessary to remove the heat
from the refrigeration system, permitting more fluid to flow when load conditions are high and less
fluid to flow when load conditions are low. The valve consists of a brass body, balance spring, valve
seat, valve disc holders, capillary tube to discharge pressure and adjusting screw.
The water regulating valve is designed to begin opening at 180 psi (1240kPa) and be fully opened at
240 psi (1655kPa). The valve is factory-set and should not need adjustment. There is significant
difference in the way standard pressure and high pressure valves are adjusted. Consult Liebert
Services.
Glycol Solution Maintenance
It is difficult to establish a specific schedule of inhibitor maintenance since the rate of inhibitor
depletion depends upon local water conditions. Analysis of water samples at time of installation and
every six (6) months should help to establish a pattern of depletion. A visual inspection of the solution
and filter residue is often helpful in judging whether or not active corrosion is occurring. The
complexity of problems caused by water requires expert advice from a water treatment specialist plus
a regular maintenance program schedule. It is important to note that improper use of water
treatment chemicals can cause more severe problems than simply using none.
Proper inhibitor maintenance must be performed in order to prevent corrosion of the glycol system.
Consult your glycol manufacturer for proper testing and maintenance procedures. Do not mix
products from different manufacturers.
Hot Gas Bypass
Operation
The hot gas bypass valve is installed between the compressor discharge piping and suction piping,
bypassing the condenser and evaporator coils. The discharge gas mixes with the suction gas, raising
the suction temperature and pressure and decreasing the mass flow through the evaporator. The
higher suction temperatures could cause compressor overheating, therefore a separate liquid
quenching valve is provided to mix refrigerant from the system liquid line with the discharge gas
before mixing with the suction gas entering the compressor.
During normal operation, when the evaporator is under full load the hot gas bypass equalizer
pressure will remain high enough to keep the valve port closed. If the evaporator load decreases, the
evaporator temperature and pressure will drop. When the suction pressure reduces below the hot gas
bypass valve setting the hot gas bypass valve opens diverting some of the refrigerant flow back to the
compressor suction. The liquid quenching valve bulb senses this increased superheat and opens,
allowing liquid refrigerant to mix with the discharge gas, desuperheating it.
Proper mixing of the three refrigerant paths ensures stable operation and system performance. The
liquid quenching valve bulb must be located downstream of all these connections to control superheat
at the compressor inlet. Superheat settings for the liquid quenching valve are chosen to maintain
consistency with the system expansion valve. During hot gas bypass operation higher superheats,
50-60°F (19-15°C), may be observed at the compressor. The liquid quenching valve is internally
equalized and superheat is not adjustable.
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Liebert Mini-Mate2 62