HVAC Unit 25 Special Refrigeration System Components Review Questions

The function of the evaporator pressure regulator is to

B) prevent a minimum pressure in the evaporator. pg 510

Which is not a basic component of the compression refrigeration cycle?

D) Suction Filter pg 509

Two types of relief valves are _______ and _______

spring loaded, one-time pg 514

Describe oil safety switch

It is used to make sure that the compressor has oil pressure when operating.

What are three main reasons why automatic pumpdown systems are used on refrigeration systems?

1. To rid the evaporator, suction line ,and crankcase of refrigerant before the off cycle and defrost cycle so migration of refrigerant to the compressor and or compressor crankcase cannot occur. 2. To prevent surges of liquid refrigerant from entering the suction port of the compressor (slugging) during start-ups. 3. To rid the crankcase of refrigerant to prevent oil from foaming during start-ups and lubrication from being robbed from the compressor's mechanical parts. pg 523

Which is not a method of low-ambient control on air-cooled equipment?

A) Modulating TXV pg 515

The purpose of the crankcase pressure-regulating valve is to

D) prevent a compressor overload condition pg 513

Two methods for accomplishing defrost on low temperature refrigeration systems are ________ and _______

Internal heat (hot gas) defrost and external (electric heating elements) pg 531

What is the function of the current sensing relay in an oil safety control scheme?

It allows the compressor to cycle on the internal overload while not affecting the operation of the oil safety controller. pg 529

What is the function of the pressure equalization orifice at the outlet of an accumulator?

It equalizes pressure on both sides of the liquid column when the compressor is on or off. It prevents liquid refrigerant from being sucked into the compressor. pg 539

What is off-cycle defrost?

It is a defrost cycle that occurs when the compressor is off. When the compressor is off, the evaporator fans will continue to run and the air in the cooler will defrost the ice from the evaporator coil. pg 530

Describe low-pressure switch

It is a device that provides low-charge protection and it also provides control of space temperature. For low-charge protection, the low pressure cutout will be set below the expected operating condition and above the atmospheric pressure of 0 psig. It also helps maintain the space temperature in the cooler. When the temperature drops, the pressure drops. When it gets to the cutout point, the compressor stops. The temperature will gradually rise and when it reaches the cut in pressure, it will start up again. pg 519

Why is there a time delay in an oil safety control?

It is built into the control to allow the compressor to get started and to prevent unneeded cut-outs when oil pressure may vary for only a moment. pg 527

What is the function of the oil return hole or orifice in a suction accumulator?

It is designed to meter the oil back to the compressor at an acceptable rate that will not cause oil foaming in the crankcase. p 538

Describe suction accumulator

It is found on the suction line and its job is to prevent liquid refrigerant from passing from the evaporator and into the compressor. pg 538

Describe the function of an oil separator

It is located in the discharge line to separate the oil from the refrigerant and return the oil to the compressor crankcase. pg 543

Describe receiver

It is located in the liquid line and is used to store the liquid refrigerant after it leaves the condenser. pg 533

Why is low-ambient control necessary?

It is needed for refrigeration that is used all year long. In the winter, the head pressure will go down to the point that the expansion valve will not have enough pressure drop across it to feed refrigerant correctly. pg 515

Describe heat exchanger

It is often found on the suction line leaving the evaporator. It provides a heat exchange between the liquid line and suction line. It improves the capacity of the evaporator by subcooling the liquid refrigerant entering it. It also prevents liquid refrigerant from moving out of the evaporator to the suction line and into the compressor. pg 537

Describe high pressure switch

It is used to keep the compressor from operating with a high head pressure. It is usually seen on water-cooled equipment. It should be set above the typical high pressure that the machine would encounter. It can be automatic or manual reset. pg 524

Describe low-ambient control switch

It is various types of controls that are used to control head pressure in refrigeration systems that operate year around or in cold weather. pg 515

What will happen if the float in an oil separator collapses?

It will cause the orifice to stay closed and not allow accumulated oil to return back to the compressor. This can cause excessive amounts of oil to accumulate in the separator. pg 544

Describe modulating fluid flow

Modulating fluid flow is throttling the amount of fluid through a gas line. Controlling the flow between maximum or no flow. pg 510

Two types of off-cycle defrost are ________ and _________

Random and planned pg 530

Describe filter drier

The filter drier is a device that removes foreign matter from the refrigerant. It can be found at any point on the liquid line after the king valve. pg 534

Briefly describe the function of a non-short-cycling or one-time automatic pumpdown system

The only way for the refrigeration system to go out of pumpdown is if the thermostat calls for cooling. pg 522

Describe pressure taps

They are line piercing valves that are bolted onto a line when a pressure reading is needed and there are not service ports on the system. pg 545

Describe the function of the electric evaporator pressure-regulating valve (EEPR)

They provide very close temperature control of the discharge air in supermarket display cases. They can move in very small increments to either open or close the suction line in response to the refrigerated cases discharge air temperatures. pg 512