| Meier
Supply
Company, Inc.
HVACR Specialists
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Pump Down Systems
A solenoid valve installed in the liquid line
can be beneficial in many ways. First, it prevents migration by isolating the
refrigerant to the condenser and receiver. Second, it allows for immediate
refrigeration without having to build head pressure.
Refrigerant vapor will always
migrate to the coldest location of a sealed system, usually the outdoor unit where the
compressor is located. The refrigerant is also attracted to the oil located in the
crankcase leads to washouts of bearings and may also break suction and discharge reed valves.
Isolating the refrigerant with a pump down solenoid is the best way to prevent any
refrigerant migration. A crankcase heater would also be beneficial in preventing
refrigerant migration.
The solenoid valve is closed when the space
thermostat is satisfied. As The system pumps down, the low side of the system
becomes short of refrigerant, lowering the pressure. The compressor is then shut off by a
low-pressure control. The setting of the L.P. control is determined by the lowest temperature
operating range of the compressor and should never allow the system to go into a vacuum.
Residual liquid refrigerant or slight leakage through the solenoid valve can cause an increase in
suction pressure, recycling the L.P. control. This will prevent any liquid refrigerant
from entering the crankcase.
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