One cause of high head pressure occurring in a refrigeration system can be （）.

If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.

A salinity indicator is used to determine the （）.

Which of the listed pumps is NOT a positive displacement pump?（）

A pressure drop through the refrigerant liquid line may cause （）.

If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.

The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.

On tank vessels equipped with power operated cargo tank valves, the type of power operator most commonly used is （）.

If the head pressure of a reciprocating refrigeration compressor is excessive, （）.

Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）