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

单项选择题The scale trap is located between the （）

A.king valve and the expansion valve
B.solenoid valve and expansion valve
C.evaporator and receiver
D.compressor and evaporator

单项选择题The relief valve is located on the（）

A.discharge side of condenser
B.discharge side of compressor
C.outlet of the evaporator
D.receiver tank

单项选择题If the compressor-discharge temperature is higher than the receiver temperature（）

A.increase the amount of cooling water to the condenser
B.decrease the amount of cooling water to the condenser
C.add more refrigerant to the system
D.remove some of the refrigerant from the system

单项选择题If the head pressure is too high,（）

A.the relief valve should open before the high-pressure cutout
B.the relief valve should open and let excess refrigerant go to receiver
C.the high-pressure cutout switch should operate before the relief valve opens
D.close in on the suction valve

单项选择题If no gaskets are used in the piping joints of a Freon system, the joints must be（）

A.finished joints
B.welded joints
C.ground joints
D.soldered joints