The humidity of the atmosphere can be determined by the use of the（）

单项选择题In a centrifugal Freon refrigeration system, the overall capacity of the system is increased by（）

A.opening more bypass lines
B.opening additional expansion valves
C.adding refrigerant
D.speeding up the machine

单项选择题The main distribution duct in an air conditioning system which contains the cooling coils and filters is called the（）

A.manifold
B.condenser
C.chamber
D.plenum

单项选择题If a compressor runs continuously, the cause might be a（）

A.defective thermal bulb
B.clogged scale trap
C.stuck high-pressure switch
D.stuck low-pressure switch

单项选择题Which of the following would not cause high suction pressure?（）

A.insufficient refrigeration
B.leaky suction valves
C.expansion valve stuck open
D.suction valve not adjusted properly

单项选择题If the high-pressure switch on the compressor opens and stops the compressor a possible cause could be:（）

A.too much cooling water going through the condenser
B.not enough refrigerant in the system
C.a leak in the evaporator coils
D.no enough cooling water going through the condenser