5
9.
After the system has operated for 15 to 20 minutes, check the compressor oil level sight glass, oil pressure
and the liquid line sight glass. If satisfactory, readjust the system temperature controller to the proper
temperature setting.
HOT GAS BYPASS SYSTEMS
SYSTEM CAPACITY CONTROL (UNITS WITH CONDENSING UNITS):
On all Bry-Air dehumidifiers equipped with refrigeration equipment, it is desirable to limit the minimum
evaporating pressure during periods of low load. This prevents coil icing and avoids operating the compressor at a
lower suction pressure than it was designed for. Several methods are used to achieve this result: integral cylinder
unloading, hot gas bypass, or both.
BYPASS TO EVAPORATOR INLET WITH DISTRIBUTOR:
The primary advantage of this method is that the system thermostatic expansion valve will provide the liquid
required for de-superheating. Also, the evaporator serves as an excellent mixing chamber for the bypassed hot gas
and the liquid-vapor mixture from the expansion valve. This ensures a dry vapor reaching the compressor suction.
Oil return from the evaporator is also improved since the velocity in the evaporator is kept high by the hot gas.
BYPASS TO SUCTION LINE WITH LIQUID INJECTION VALVE:
With this method, hot gas is bypassed directly into the suction line downstream of the main thermostatic
expansion valve's bulb. An auxiliary thermostatic expansion valve, commonly called a de-superheating thermostatic
expansion valve or a liquid injection valve, is required.
The purpose of this valve is to supply enough liquid refrigerant to cool the hot discharge gas to the recommended
suction temperature. The liquid injection valve is matched to the hot gas bypass valve at the factory and adjusted.
However, it may be field adjusted if necessary.
A suction line accumulator is installed downstream of the bypass connection with the auxiliary thermostatic
expansion valve bulb down stream of the accumulator to ensure a good mixture of bypassed hot gas and liquid-
vapor.
NOTE:
On systems with remote condensers, special care must be taken in the system piping to accomplish
satisfactory oil return to the compressor from the low side.
HEAD PRESSURE CONTROL:
In order to achieve proper system operation, it is necessary that adequate discharge pressures be maintained to
insure that the expansion valve will feed correctly to prevent low suction conditions. The expansion valve is sized
