Practice Test A

The four main components of a refrigeration system are

• compandium tube, cooler, hot coil, & compressor

• compressor, condenser, evaporator, & metering device

• eliminator, pressure-enthalpy device, refrigerant, & oil separator

• receiver, sight glass, accumulator, and compressor

Answer explanation

Refer to the Basic Refrigeration System Cycle.

In a three-phase system, the voltage imbalance between any two legs may not vary by more than:

• 10%

• 5%

• 2%

• 1%

Answer explanation

A voltage imbalance of more than 2% between any two legs of the supply voltage applied to a three-phase compressor motor must be corrected. A small imbalance in the input voltage results in a considerable amount of heat being generated in the motor windings. With only 5% imbalance, the winding temperature can increase as much as 50% over safe level.

When using a thermostatic expansion valve with a __________ charged element, hunting can be considerably reduced.

• gas

• liquid

• cross

• parallel

Answer explanation

The operating characteristics of cross charge inherently reduce hunting. Cross-charged expansion valves are used on applications from +50 degrees F to -100 degrees F particularly where repetitive pull down cycles are encountered.

The refrigerant line that connects the condenser to the metering device is ___________ line.

• discharge

• expansion

• liquid

• suction

Answer explanation

Refer to the Basic Refrigeration System Cycle.

What is the maximum allowable current imbalance rating in a three-phase supply?

• None

• 2%

• 5%

• 10%

Answer explanation

Current imbalance between any two legs of a three-phase system may not exceed 10%. voltage imbalance will always produce current imbalance, but a current imbalance may occur without a voltage imbalance. This can happen when an electrical terminal, contact, etc. becomes loose or corroded, causing a high resistance in the leg. Since current follows the path of least resistance, the current in the other two legs will increase, causing more heat to be generated in those two windings.

Lithium-Bromide is used in absorption systems as:

• a salt solution

• an absorbent (attractant)

• a solution that creates a pressure difference

• All Answers

Answer explanation

Absorption air-conditioning chillers are considerably different from compression cycle chillers. They utilize heat as the driving force instead of the compressor. This type of equipment utilizes water for the refrigerant and certain salt solutions that have enough attraction for water to create a pressure difference. The salt solution used as the absorbent or attractant is lithium-bromide (Li-Br). This liquid solution is diluted with distilled water. This solution is very corrosive and the system must be kept very clean.

Atmospheric pressure at sea level is:

• 0 psi

• 14.7 psi

• 32 psi

• 212 psi

Answer explanation

A column of this atmosphere one inch square and extending from sea level up to its maximum height (taken to be about 600 miles) weighs 14.7 pounds. Thus, the pressure at sea level is 14.7 psi.

The difference between a contactor and a motor starter is:

• physical size

• overload protection

• wire size

• timing

Answer explanation

The starter is the same as the contactor, except for the addition of the overload relays and their wiring connections.

When an object is refrigerated:

• some of its heat energy is destroyed.

• heat is removed from it.

• more cooling is added.

• its molecules move faster.

Answer explanation

Refrigeration is the transfer of heat from one place to another by a change in state of a liquid. Cold or coldness is an absence of heat, just as darkness is an absence of light or quietness is an absence of sound.

The device that is incorporated into a vacuum steam heating system to protect the vacuum pump from creating too low (deep) a vacuum is a:

• relief valve

• control line

• vacuum switch

• vacuum breaker

Answer explanation

Vacuum breaker. Is incorporated into the system to protect the vacuum pump from creating too low a vacuum. The pump will be adversely affected if the induced vacuum the pump creates is too low. A vacuum breaker is incorporated into the pump to protect the vacuum pump from creating too low a vacuum. The vacuum breaker will open and let air into the system when the pressure inside the pump drops down to 15” of mercury.