Low compressor head pressure in a refrigeration system can be caused by（）.

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

The general purpose of a heat exchanger is to （）.

Which of the following statements is correct concerning heat transfer?（）

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

An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

The rate of heat transfer from a hot region to a cold region is affected most by the （）.

An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.

A salinity indicator is used to determine the （）.