Practice Test C

The most accurate thermometer is the

• glass stem thermometer

• electronic thermometer

• dial-type thermometer

• pocket dial-type thermometer

Answer explanation

HVACR Training Manual Unit 11 Calibrating Instruments 11.3 Temperature-Measuring Instruments. Page 207.

Glass thermometers often cannot be calibrated because the graduations are etched on the stem. If the graduations are printed on the back of the instrument, the back may be adjustable. A laboratory-grade glass thermometer is certified as to its accuracy, and it may be used as a standard for field instruments. It is a good investment for calibrating electronic thermometers.

The purpose of the compressor is to change

• low-pressure, low-temperature liquid to a high-pressure, high temperature liquid

• high-pressure, high-temperature vapor to a low-pressure, low-temperature vapor

• low-pressure, low-temp vapor to a high-pressure high-temp vapor

• high-pressure, high-temperature liquid to a low-pressure, low-temperature liquid

Answer explanation

HVACR Training Manual Unit 3 Refrigeration and Refrigerants 3.8 The Compressor. Page 32. The compressor can be considered a vapor pump. It reduces the pressure on the low-pressure side of the system, which includes the evaporator, and increases the pressure in the high-pressure side of the system. This creates refrigerant flow from the low-pressure side to the high-pressure side. All compressors in refrigeration  systems perform this function by compressing the vapor refrigerant.

Typical suction superheat at the evaporator of an air conditioning system is expected to be:

• 10 degrees F to 20 degrees F

• 12 degrees F to 15 degrees F

• 20 degrees F to 25 degrees F

• 60 degrees F to 80 degrees F

Answer explanation

Refrigeration Mechanical Equipment Service Manual Volume One

Chapter 15: Application of the Thermostatic Expansion Valve

Pages 197 and 198.

Adjustment of a thermostatic expansion valve means adjusting the spring tension so that the valve controls at the desired value of superheat. The proper value of superheat is usually established by the manufacturers of the equipment, and their recommendations should be followed. As a general rule, the superheat setting for a relatively high temperature application, such as air conditioning, might be 10 to 15 degrees; for low temperature applications, the superheat probably should not exceed 10 degrees.

Condenser saturation temperature on a air cooled condenser should be higher than the ambient temperature by:

• 100 degrees F to 105 degrees F

• 90 degrees F to 100 degrees F

• 10 degrees F to 15 degrees F

• 30 degrees F to 35 degrees F

Answer explanation

HVACR Training ManualUnit 22 Condensers22.5 Air-Cooled Condensers.

Page 411.

Air-cooled condensers have a relationship to the temperature of the air passing over them. The refrigerant inside the coil will normally condense at 30 degrees F higher than the air passing over it (also known as the ambient air). This statement is true for most standard-efficiency condensers that have been in service long enough to have a typical dirt deposit on the fins and tubing. The relationship can be improved by adding condenser surface area. With the outside air temperature of 95 degrees F, the condensing temperature will be about 125 degrees F.

A pressure switch that contains a high and a low switch is called a:

• thermostat

• humidistat

• time clock

• dual-pressure switch

Answer explanation

Basic Electricity Chapter 16: Motor Controls Question 9. Page 120.

A pressure switch is a device that opens or closes a set of contacts when a certain pressure is applied to the diaphragm of the switch. Pressure switches can be used as safety devices or as main operating controls. The switches also can be used to operate other parts of the system.

There are two types of pressure switches used to in the piping industry. A nonadjustable pressure switch is used by many manufacturers to prevent the pressure switch from changing. An adjustable pressure switch can be used to meet any specific need that might arise. Adjustable pressure switches usually are obtained for field replacement of a pressure switch. Pressure switches also can be classified as high pressure, low pressure, or dual-pressure switches ( a combination of both). Pressure switches can be obtained for almost any purpose that would arise in the industry.

Refrigerant and / or oil out of place or composition in the refrigerant system is known as:

• loss of oil

• lack of lubrication

• loss of refrigerant

• pure motor failure

Answer explanation

Refrigeration Mechanical Equipment Service Manual Volume One Chapter 17: Refrigerant Piping Accessories

Page 215.

If an excessive quantity of oil remains out in the system, oil in the compressor crankcase may fall to too low a level to permit adequate lubrication of the compressor.

Autopsy on A Compressor Copyright 1978, By Burl C. Brown Item 1 Valve Plate Inspection Page 7.

“Lack of lubrication” could be described as any time the oil or refrigerant is not where it belongs in its normal physical condition. These conditions might be as follows:

a. Oil returning to the compressor as a slug

b. Refrigerant returning to the compressor as a slug

c. Refrigerant returning to the compressor as a liquid

d. Oil excessively hot

e. Refrigerant highly superheated

f. Loss of oil

g. High operating temperatures

The economizer might be described as:

• a controllable damper.

• a compressor cylinder bypass.

• a return air system.

• an indoor air recirculating system.

Answer explanation

Carrier Service Tech Training GT44-01 Copyright Carrier Corporation 1992 020-504 Rooftop Economizers Question 1. Page 1 An economizer is really just a controllable damper or door arrangement that allows a rooftop air conditioner to bring in a variable amount of outdoor air.

The compression ratio in a system can be determined by:

• multiplying discharge gage pressure by suction gage pressure

• dividing discharge pressure absolute by suction pressure absolute

• dividing suction pressure absolute by discharge pressure absolute

• subtract suction pressure absolute from discharge pressure absolute and divide by 12,000 btu/hr

Answer explanation

Refrigeration Mechanical Equipment Service Manual Volume OneChapter 9: Reciprocating Compressors

Page 108.

The compression ratio of a compressor is the ratio of the absolute discharge pressure (psia) to the absolute suction pressure (psia):

Compression Ratio = DischargePSIA Divided by SuctionPSIA

Note that compression ratio is always based on absolute pressures.

If not properly installed, a hot-gas muffler might trap:

• hot gas.

• superheated vapor.

• suction gas.

• oil.

Answer explanation

Refrigeration Mechanical Equipment Service Manual Volume One Chapter 17: Refrigerant Piping Accessories Question 9.

Page 217.

The muffler is installed in the discharge line as close as possible to the compressor. Due to their construction, mufflers usually form natural oil traps unless properly installed.

How many Btu are there in 8 kW of electrical power?

• 26,286

• 5,968

• 27,304

• 68,260

Answer explanation

HVACR Training Manual

Unit 2 Matter and Energy

2.14 Electrical Power ------ The Watt  Page 21.

The unit of measurement for electrical power is the watt (W).

Converting electric heat rated in kilowatts (kW) to the equivalent gas or oil heat rated in Btu. Suppose that we know the capacity in Btu for a 20-kW electric heater(a kilowatt is 1000 watts). 1 kW = 3413 Btu.20 kW X 3413 Btu/kW = 68,260 Btu of heat energy

Converting Btu to kW. Suppose that a gas or oil furnace has an output capacity of 100,000 btu/h. Since 3413 Btu = 1 kw, we have100,000 Btu divided by 3413 Btu/kW = 29.3 kW

In other words, a 29.3 -kW electric heat system would be required to replace the 100,000-Btu/h furnace.

3.413 Btu = 1 W. 1 kW (1000 W) 3.413 X 1000  =  3413 Btu.3413 Btu x 8 kW = 27,304 Btu’s