LESSON 1 TO 10 HEAT PUMPS

When ice forms on the outdoor coil of a heat pump during the heating cycle in winter, defrost must be initiated before the air flow across the coil is reduced by more what percentage?

50 percent ((Ref: 155/3))

At what liquid-line temperature does a temperature-activated defrost control typically terminate the defrost cycle?

50 to 65°F ((Ref: 91/3))

Convert 68 degrees F to an equivalent Celsius temperature.

68 degrees minus 32, divided by 1.8 = 20 degrees Celsius ((Ref: 7/2))

When multiple switches are connected in series with each other, they all must be in the position in order for the circuit to be energized.

Closed ((Ref: 148/4))

What type of heat pump systems are well suited for applications in which heating is required in some zones while cooling is required in others?

Closed-loop water-source heat pumps ((Ref: 43/2))

What effect does compression have on the temperature and density of refrigerant vapor?

Compressing the vapor increases both its temperature and density. ((Ref: 102/3))

The latent heat of BLANK causes a change in phase from vapor to liquid. The latent heat of BLANK causes a change in phase from liquid to vapor.

Condensation, vaporization. ((Ref: 6/1))

SEER is a measure of a heat pump's BLANK. It is expressed in units of BLANK.

Cooling efficiency, Btu/watt. ((Ref: 97/3))

What guidelines should be followed when the cooling capacity of a heat pump is oversized to reduce the amount of auxiliary heat that will be required in the winter?

In colder climates, the cooling capacity may be oversized by 25%. In milder climates, the cooling capacity may be oversized by 15%. ((Ref: 49/2))

A normally open contact is open when the power to the unit is on or off?

off ((Ref: 149/3))

The indoor section of an air-to-air split system, when installed in an attic, should be placed in a(n) BLANK.

Overflow pan. ((Ref: 38/2))

York OEM Defrost Control Circuit Board.

PN CIB31019871

A cooling anticipator is connected in BLANK with the thermostat switch and is energized during the BLANK cycle.

Parallel, off Ref: 193/2

What is meant by "excessive" supplemental heat?

More heat than would be required to neutralize the cooling effect that occurs during the defrost cycle. ((Ref: 87/2))

Rotary compressors are marginally BLANK efficient and BLANK noisy than similarly sized reciprocating compressors.

More, less ((Ref: 112/2))

How is the power input to a three phase electric heater calculated?

Multiply the average current draw of the three lines supplying power to the heater times the average impressed voltage times a factor of 1.73 to find the power input in watts. Divide by 1,000 to find the kilowatt input to the heater. (Ref: 249/1)

How is the power input to a single phase electric heater calculated?

Multiply the current draw times the applied voltage to find the power input in watts. Divide by 1,000 to find the kilowatt input to the heater. (Ref: 248/4)

A potential start relay has normally open or normally closed contacts?

Normally closed. Ref: 171/2

What determines the speed of a motor?

Number of poles, frequency of the current. Ref: 179/2

Explain why a supplemental heating source may be needed in a heat pump application.

On very cold days, the heat available from the ambient air is not sufficient to heat a home using a heat pump. (Ref: 247/1)

What is the best type of filter-drier for general use?

One that has the ability to remove moisture, acid, and sludge, and to filter solid particles. ((Ref: 131/6))

What is the function of outdoor thermostats used in conjunction with electric heaters in heat pump applications?

Outdoor thermostats are used to limit the number of stages of resistive supplemental heating that can be energized, based on the ambient temperature. (Ref: 252/4)

What is the only method of checking superheat that yields an accurate value?

Taking pressure and temperature readings at the evaporator outlet. ((Ref: 124/5))

In which component of a refrigeration system is heat removed?

The Condenser. ((Ref: 17/3))

What initiates a demand defrost cycle?

The difference in temperature between the outdoor coil and the ambient air. ((Ref: 158/2))

What actions must be taken when a fusible link opens due to high operating temperatures?

The link must be replaced and the cause of the overheating must be found and corrected. (Ref: 252/2)

What is droop?

The lowering of the thermostat's operating temperature below the set-point, due to the heating of the bi-metal by the heat anticipator. Ref: 194/1 , 2

What is the "critical point" of a refrigerant?

The maximum saturation condition at which evaporation and condensation may occur. ((Ref: 71/4))

Basic heat pump control strategy calls for which heat source to be used first?

The most economical. Ref: 190/3-191/1

How does the resistance of dry human skin compare to that of wet human skin?

The resistance of human skin when it is dry is 100,000 to 600,000 Ohms. When it is wet, its resistance is only 1,000 Ohms. (Ref: Table 10-5)

When checking the operation of a defrost control, what action may you need to take at the termination sensor?

When you advance the frequency setting to check operation, you will need to jumper the termination temperature sensor if the refrigerant is warmer than its closing temperature. (Ref: 221/2)

Is the output capacity of a heat pump chosen to match the heating load or the cooling load of a building? Why?

Chosen to match the cooling load, to ensure that humidity will be controlled in the conditioned space during summer operation. (Ref: 247/2)

Which direction should you turn the adjustment screw of a Dwyer pressure activated defrost control if you wish to increase the amount of ice formation required to initiate defrost?

Clockwise. (Dwyer 1910) (Ref: 221/1)

What is the equation for converting watts to horsepower?

Horsepower = watts divided by 746 ((Ref: 114/1))

What level of electric current through the human body causes muscular contractions so severe that the heart will stop beating?

200 Millie Amps or more Ref: Table 10-6

A fusible link in an electric heater typically opens at a temperature of approximately how many degrees.

215°F (Ref: 252/2)

What is the most common type of heat pump used in residential applications?

Air-to-air split system. ((Ref: 36/1))

An electric duct heater requires a minimum air velocity of 900 ft/min and has a cross sectional free opening area of 10 inches by 22 inches. What is the minimum air volume (in cfm) required?

10 inches times 22 inches = 220 square inches of the ductwork. 220 square inches divided by 144 = 1.528 Square feet. 1.528 square feet times 900 ft/min = *1,375 cfm*. (Ref: 260/2-261/1)

Typical superheat values measured at the evaporator outlet of a properly operating heat pump system is about how many degrees?

10 to 12 degrees F ((Ref: 124/2))

Absolute zero on the Fahrenheit scale is BLANK degrees F

-460 degrees F ((Ref: 7/2))

List three heat sources and heat sinks, and explain the main advantages of each.

1) Air. It is abundant and allows for use of equipment that is economical to install and operate. 2) Water. Large amounts of heat can be transferred, and the volume of water needed is much less than the volume that would be required if air were used. 3) Earth. Ground-source equipment provides for consistent temperatures of heat transfer fluids, which often makes the use of auxiliary heating components unnecessary. ((Ref: 32/3-34/6))

Describe the procedure for checking the accuracy of the temperature sensor used in solid-state demand defrost controls.

1) Check the temperature of the sensor by placing the lead of a temperature tester on the tube near the sensor and insulate the bulb. 2) Unplug the sensor and measure the resistance as quickly as possible to prevent the meter current from changing the resistance reading. 3) Refer to a chart for the sensor used to determine whether the measured resistance corresponds correctly to the measured temperature. (Ref: 242/5, 6)

List at least three precautions that you should observe when installing any new thermostat.

1) Disconnect the power supply to prevent electric shock or equipment damage. 2) Do not short across coil terminals on a contactor. 3) Run wires as close to the subbase as possible. 4) Keep wire length to a minimum. 5) Push excess wire back into the hole in the wall, and plug the hole to prevent drafts from affecting thermostat operation. 6) Do not over tighten thermostat's captive mounting screws. Ref: 205/2

List at least three of the ways in which heat pumps are classified.

1) Heat source and sink 2) Heating and cooling distribution fluid 3) Thermodynamic cycle 4) Building structure 5) Capacity and configuration 6) Limitation of the source and sink ((Ref: 35/4))

List four possible causes of a compressor motor overload condition.

1) High current draw caused by a refrigerant overcharge 2) High system loads on either the evaporator or the condenser 3) Excessively high return air temperatures entering the evaporator 4) High suction superheat caused by a refrigerant undercharge ((Ref: 117/1))

What four factors must you check before attempting to adjust any defrost control?

1) The refrigeration system must be properly charged. 2) The indoor coil must be clean, and indoor air flow correct. 3) The outdoor coil must be clean, with no restrictions to air flow. 4) The outdoor fan motor must be wired to the proper voltage. (Ref: 214/5)

What three primary functions must all defrost controls perform in removing frost or ice from the outdoor coil of a heat pump?

1) The reversing valve must be switched to the cooling mode, making hot gas available to the outdoor coil for ice melting. 2) The outdoor fan motor must be de-energized, stopping air flow through the coil to speed the melting process. 3) Supplemental heat must be made available indoors to keep the room temperature from dropping while the unit is defrosting. (Ref: 215/1)

List three reasons for using a multiple-stage thermostat to control a heat pump.

1) The use of auxiliary heat is governed by actual demand. 2) The compressor does not start at the same time as the auxiliary heat, thus spreading out the starting electrical loads. 3) During periods of high load, the heat pump runs constantly instead of being cycled. Ref: 191/3

What is the synchronous speed of a six-pole motor operating on power supplied at a frequency of 60 Hz?

1,200 rpm ((Ref: 116/1))

What is the synchronous speed of a four-pole motor operating on a 60-Hz power supply?

1,800 RPM 120 times 60 divided by 4 equals 1,800 RPM Ref: 179/2

What is the typical override period for defrost controls used in single-speed heat pumps?

10 to 12 minutes. Ref: 241/3

Tempstar Heat Pump Defrost Control Circuit Board

1069364

ICP/Tempstar/Heil/Comfort Maker Defrost Control Circuit Board

1087562

One atmosphere of pressure, atmospheric pressure at sea level, is equivalent to BLANK pounds per square inch absolute.

14.696 pounds per square inch absolute ((Ref: 8/2))

The heat anticipator in the circuit controlling a heat pump should be set for BLANK % of the current draw of the control circuit.

140% Ref: 192/2

What indoor air volume (expressed in cfm) would be required for a heating unit that has a 45°F temperature rise and an output of 70,000 Btuh?

1440 cfm CFM = BTU divided by delta T times 1.08 ((Ref: 51/2))

What level of electric current through the human body causes the loss of muscular control, making it impossible for a person to let go of an electrical wire?

15 to 20 Millie Amps (Ref: Table 10-6)

When the heat loss of the home is at 50% of the maximum design load and the thermostat is properly adjusted, a heat pump should cycle how many times an hour?

2 to 3 times an hour Ref: 192/2

Outdoor thermostats should be set to activate supplemental heat when the outdoor ambient temperature is BLANK °F higher than the calculated balance point.

2 to 3°F ((Ref: 49/1))

When multiple outdoor thermostats are used in a heat pump system, each thermostat is set how many degrees higher than the thermal balance point of the preceding stage, as calculated by using a balance point chart or graph for the specific heat pump installed.

2 to 3°F (Ref: 253/2)

A heat pump thermostat is set so that there will be a dead-band range of about BLANK °F between the heating and cooling cycles. A closer setting might result in BLANK .

2 to 4 °F, frequent cycling. ((Ref: 95/1))

Rotary compressors generally are used in heat pumps with capacities of less than BLANK tons.

2 tons ((Ref: 111/3))

The control voltage used in typical residential heat pump systems is how many volts?

24 volts ((Ref: 147/2))

Convert 25 degrees Celsius to an equivalent Fahrenheit temperature.

25 times 1.8, plus 32 = 77 degrees F ((Ref: 7/2))

Reversing valves can withstand a temperature of approximately how many degrees during installation?

250 degrees ((Ref: 139/2))

At what head pressure does a pressure activated defrost control typically terminate the defrost cycle?

250 to 300 Pounds per square inch guage ((Ref: 91/2))

What is the typical range of refrigerant temperatures at which the outdoor sensor closes?

26 to 28°F (Ref: 215/2)

The typical compression ratio for a heat pump operating in the cooling mode is approximately BLANK

3 to 1 ((Ref: 96/7))

One kilowatt (1 kW) of input to an electric furnace produces approximately how many Btuh of heating output.

3,413 Btu per hour (Ref: 248/3)

How much auxiliary heat will be required on a design day when a home heat loss is 35,600 Btuh and the heat pump output is 17,200 Btuh?

35,600 Btu per hour minus 17,200 Btu per hour divided by 3,413 Btu per hour = 5.39 kW ((Ref: 54/1))

What is the maximum total current draw of a single duct heater circuit?

48 Amps (Ref: 253/3)

A thermostat should be mounted approximately how many feet above the finished floor in an area that has good air circulation at average room temperature.

5 feet Ref: 205/4

When two duct heaters are installed in series in the same duct, what is the minimum distance that must be maintained between the upstream heater and the downstream heater?

5 ft (Ref: 259/1 (13))

Frost can begin to form on the outdoor coil of an operating heat pump when the ambient air temperature is as high as BLANK °F.

50 degrees F (Ref: 213/1)

One horsepower (1 hp) of mechanical energy is equivalent to BLANK watts of electrical energy, and one watt (1 W) of electrical energy is equivalent to BLANK Btu of heat energy.

746 Watts, 3.413 Btu ((Ref: 3/4, 5))

The start capacitor in a capacitor-start, capacitor-run motor is switched out of the circuit when the motor has achieved ___________ % of full speed.

75 to 80% ((Ref: 113/4))

The supplemental heating capacity of a heat pump system should be equal to BLANK % of the design heat loss to provide the heat needed during defrost and emergency heat periods.

75 to 80% ((Ref: 56/6))

A start capacitor used in a heat pump system is removed from- the circuit when the motor reaches approximately what percentage of its operating run speed.

75% ((Ref: 155/1))

What is the coefficient of performance (COP) of a heat pump?

A comparison of how much heat the heat pump is producing compared to how much heat an electric furnace would produce using the same amount of electricity. ((Ref: 95/4))

If a system operates correctly in one cycle and pumps down when switched to the other cycle, what problem is indicated?

A defective TEV or a stuck check valve. In such cases, the power element could be defective ((Ref: 126/3))

Define work.

A force moving an object in the direction of the force. ((Ref: 3/3))

How much clearance should be allowed between an electric heating element and supporting structures or cabinet?

A minimum clearance of 1/4 inch is required around electric heater coils. (Ref: 250/1)

What device is used to reduce or prevent indoor temperature swings during winter operation?

A negative coefficient thermistor (outdoor temperature sensor). ((Ref: 158/6-159/1))

Describe in simple terms the basic process by which a refrigerant transfers heat energy.

A refrigerant is used to transfer heat when it changes states. When liquid refrigerant evaporates into a vapor, heat is absorbed by the vapor. When refrigerant vapor is condensed into a liquid, heat is rejected from the refrigerant. ((Ref: 2/3))

In your own words, state the second law of thermodynamics.

A temperature difference must exist between two materials in order for heat energy to travel. ((Ref: 3/7))

What is the main difference between an open compressor and a Hermetic compressor?

An open compressor does not have the motor in the same housing as the compressor. A hermetic compressor has the motor and compressor housed in the same welded shell. ((Ref: 102/1))

Explain what is meant when transformers are referred to as "constant-power'' devices.

Any power consumed in the secondary must come from the primary. Ref: 177/1

At what outdoor ambient temperature will the refrigerant temperature in the outdoor section be approximately 26°F?

Approximately 40°F. (Ref: 233/3)

What distance must be maintained between an electric duct heater and any turn or elbow in the ductwork?

At least 48 inches, If less than 48 inches is available between the heater and an elbow, turning vanes must be provided, in which case the absolute minimum distance is 24 inches. (Ref: 254/1 (5))

A pressure drop equivalent to how many degrees across the evaporator of a heat pump system is considered to be of consequence and would require a expansion valve with an external equalizer?

At or above 2 degrees Fahrenheit. Example: R22 equals 1.5 pounds per square inch per degree. A 3 pounds per square inch pressure drop (2 times 1.5 = 3) would require a external equalizer. ((Ref: 124/4))

Why is active defrost typically not needed when frost forms on an outdoor coil operating in ambient temperatures higher than 40 to 45°F?

At warmer ambient temperatures, heating cycles will be short enough that the outdoor air will melt the frost during off cycles. (Ref: 213/1)

What component may be used to allow a conventional refrigerant distributor to function in a heat pump system?

Auxiliary side connector tees permit the conversion of conventional refrigerant distributors to reverse-cycle service. ((Ref: 128/2))

Why does a heat pump require three-function control?

Because a heat pump performs three functions-it provides cooling, it provides heating, and it must defrost the outdoor coil when ice forms on it. ((Ref: 88/4))

The maximum air velocity recommended by the manufacturers of most electric duct heaters is typically how many feet per minute?

Between 2,000 and 2,500 ft/min (Ref: 261/2)

Where in the refrigerant circuit is an accumulator located?

Between the reversing valve and the compressor inlet. ((Ref: 137/2))

Describe the main differences between a heat anticipator that utilizes voltage anticipation and one that utilizes current anticipation.

Both heat anticipators are connected in series with the thermostat switch. The voltage anticipator is connected in parallel with the low-voltage load and is a fixed anticipator. The current anticipatory is connected in series with the low-voltage load and is adjustable. Ref: Figure 8-2

How is the compression ratio of an operating heat pump calculated?

Both the high-side and low-side refrigerant pressures must be converted to absolute pressure values by adding 14.7 pounds per square inch to each gauge reading. The absolute high-side (discharge) pressure is divided by the absolute low-side (suction) pressure to determine the compression ratio. ((Ref: 103/1))

Bryant - Carrier Heat Pump Defrost Control Board

CESO110063-02

Unless otherwise noted, all wiring diagrams depict switches and contacts in what mode?

Deenergized ((Ref: 149/3))

What causes "droop" in cold weather? What component is used in heat pump systems .to reduce the amount of droop experienced?

Droop is caused by the thermostat's heat anticipation. In heat pumps, an additional circuit is provided that makes use of an outdoor thermistor sensor to reduce droop. Ref: 184/2

How is droop compensated for when outdoor reset is used?

Droop is counteracted by calibrating the thermostat high by 5°F, which is the amount of offset expected. Ref: 194/4, 5

Which type of supplemental heating equipment is most common in heat pump applications?

Electric resistive heaters. (Ref: 247/1)

What is the advantage of using electronically commutated motors (ECMs) in heating and air conditioning systems?

Electronically commutated motors (ECMs) can be used to vary motor speeds, improving system efficiency and lowering operating costs. Ref: 180/1

In your own words, state the first law of thermodynamics.

Energy can neither be created nor destroyed, but can be changed from one form into another. ((Ref: 3/2))

The indoor coil of a heat pump system serves as the BLANK during the cooling season, and as the BLANK during the heating season.

Evaporator during the cooling season, condenser during the heating season. ((Ref: 16/6))

How is factory-installed wiring differentiated from field-installed wiring on a schematic diagram?

Factory-installed wiring normally is indicated with solid lines, and field-installed wiring with dashed lines. Power circuits may be indicated with thick or heavy lines, and control wiring with thinner or lighter lines. ((Ref: 148/3))

Define pressure

Force per unit of area. ((Ref: 8/2))

Temperature is a measurement of heat BLANK. British thermal units and calories are measurements of heat BLANK.

Heat Intensity, heat quantity ((Ref: 5/1))

Why are suction-line accumulators and crankcase heaters often required to protect heat pump compressors?

Heat pump compressors are subject to collecting liquid refrigerant in the compressor crankcase during the "off" cycle. Liquid refrigerant in the crankcase results in poor lubrication on start-up and increases wear on the compressor bearings. ((Ref: 64/1))

When troubleshooting the Robertshaw defrost control, you must check the system refrigerant charge in the what mode if the ambient temperature is below 65°F?

Heating mode (Ref: 229/1)

Heat always travels from a(n) BLANK material to a(n) BLANK material.

Higher-temperature, lower-temperature. ((Ref: 37-4/1))

In the cooling mode, which coil (indoor or outdoor) of a heat pump system functions as the condenser? Which coil functions as the condenser in the heating mode?

In the cooling mode, the outdoor coil functions as the condenser. In the heating mode, the indoor coil functions as the condenser. ((Ref: 66/1, 67/5))

Which pressure scale has the greater resolution, one calibrated in inches of mercury or one calibrated in inches of water column?

Inches of water column. ((Ref: 8/4-9/2))

One of the most important principles of refrigeration is that an increase in pressure on a liquid results in a(n) BLANK in the liquid's boiling temperature.

Increase in the liquid's boiling temperature. ((Ref: 68/3))

Voltage produced in the secondary winding of a transformer is called the BLANK voltage.

Induced voltage or the secondary voltage. Ref: 176/6

The vapor line from the indoor section to the outdoor section of a split System must be BLANK to prevent unwanted heat transfer.

Insulated. ((Ref: 38/5))

What happens to the resistance of a negative coefficient thermistor as the temperature increases?

It decreases.

What is the advantage of the "adaptive" capability of modern solid-state defrost controls?

It provides defrost on demand, rather than defrost by timed cycle (Ref: 239/2)

What is the difference between latent heat and sensible heat?

Latent heat causes a change in the state of a substance without a change in its temperature. Sensible heat causes a change in the temperature of substance without a change in its state. ((Ref: 6/1))

State at least three of the five laws of heat transfer.

Law 1: Heat exists in the air at all temperatures. Law 2: Heat flows from a region of higher temperature to a region of lower temperature, regardless of how slight the temperature difference might be. Law 3: All gases become warmer when they are compressed. Law 4: Most matter can exist as a solid, liquid, or gas. Law 5: The temperature at which a material changes from a liquid to a gas, or from a gas to a liquid, depends on the pressure to which it is subjected. ((Ref: 32/2))

What line voltages typically are used in residential and light commercial heat pump applications?

Line voltage may vary from 115 Volts single phase used in some mini-split heat pumps to 460 Volts three-phase used in some commercial units. The most common is 208/230 volts. ((Ref: 164/2))

Does a shaded-pole motor have a high starting torque or a low starting torque?

Low starting torque. Ref: 177/5

Are low-voltage thermostats or line-voltage thermostats generally recommended for use in residential heat pump applications?

Low-voltage. Ref: 189/3

TEVs that limit the pressure created by an expanding bulb charge are called what?

Maximum operating pressure (MOP). ((Ref: 124/5-125/1))

The type of motor in which the capacitor is never taken out of the circuit is called what kind of motor?

Permanent Split Capacitor motor (PSC) Ref: 170/2

List four components that are typically part of the power circuits in a heat pump system.

Power circuits include the components that require line voltage, such as the compressor, condenser fan motor, indoor blower motor, and electrical resistance heaters. ((Ref: 147/2))

A numerical value (always less than 1) that describes the relative amount of true electric power, in watts, that is actually delivered to a motor is called the motor's _______

Power factor. ((Ref: 114/1, 2))

Wiring diagrams generally are divided into two parts, what are they?

Power, control. ((Ref: 147/1))

What factors determine the proper size of a TEV?

Proper TEV size is determined by the Btuh load requirement, the pressure drop across the valve, and the evaporator temperature. ((Ref: 122/3))

What three types of compressors are used in residential heat pump applications?

Reciprocating, scroll, and rotary. ((Ref: 102/1))

A heat anticipator is a(n) BLANK that is connected in with the thermostat switch.

Resistor, series. Ref: 19211

What other names are used for reversing valves?

Reversing valves also are called switchover valves or four-way valves. ((Ref: 138/1))

10. A permanent split-capacitor motor can be identified by the presence of a(n) BLANK in the motor circuit.

Run capacitor. Ref: 112/6-113/1

Are safety switches connected in series or parallel?

Series ((Ref: 148/4))

What is specific heat?

Specific heat is the energy required to raise the temperature of 1 lb of a substance by 1 degree F. ((Ref: 6/3))

What are the three main functions performed by capacitors in ac motor circuits?

Starting the motor, limiting the running current, and improving the power factor. Ref: 168/2

The greater the phase shift between a motor's run winding and start winding currents, the higher the of the motor.

Starting torque. Ref: 168/4

The upper scroll in a scroll compressor is the BLANK scroll, and the lower scroll is the BLANK scroll.

Stationary (or fixed), driven (or orbiting). ((Ref: 108/1))

A transformer with a higher number of turns in the secondary coil than in the primary coil is called a(n) BLANK transformer.

Step up transformer. Ref: 176/6

What will happen if the heat anticipator setting is lower than the recommended value?

Such a setting will result in shorter on cycles. Ref: 192/2

The motor in a hermetic compressor is cooled by?

Suction vapor. ((Ref: 105/4))

A typical reversing valve is a cylinder with three tubes on one side and a single tube.on the other side. The center tube of the three tubes is always the compressor BLANK connection. The single tube on the opposite side of the cylinder is always the compressor BLANK connection.

Suction, discharge. ((Ref: 93/2))

Heat pump systems with line sets longer than 80 ft require the use of a(n) BLANK to protect the compressor from flood-back on start-up.

Suction-line accumulator ((Ref: 39/4))

What is superheat?

Superheat is energy that raises the temperature of a vapor above its saturation temperature. ((Ref: 6/4))

The physical properties of a refrigerant may be represented as a curve on a pressure enthalpy diagram. Plot points that fall outside and to the right of the curve indicate that the refrigerant is a(n) BLANK . Plot points that fall outside and to the left of the curve indicate that the refrigerant is a(n) BLANK. Plot points that fall inside the curve itself indicate that the refrigerant is a(n) BLANK.

Superheated vapor, sub-cooled liquid, mixture of saturated liquid and vapor. ((Ref: 71/2))

If an electric heater rated for operation at 240 volts, single-phase power is operated at 208 volts, how will the actual heating output relate to the rated output?

The actual heating output will be 75% of the rated output. (Ref: 265/2)

What determines the capacitance value of a capacitor?

The area of the capacitor plates and the distance that the plates are separated by the dielectric. The strength of the dielectric is also a determining factor. Ref: 168/5

What three forces are necessary to operate a thermostatic expansion valve (TEV)?

The bulb pressure, the evaporator pressure, and the spring force. ((Ref: 122/1))

How will the air flow volume (cfm) change if the speed of a fan (rpm) is increased by 10%?

The cfm will change in direct proportion to changes in rpm, the cfm also will increase by 10%. Ref: 182/1 (1)

Define the coefficient of performance (COP).

The coefficient of performance is the ratio of the heat delivered by a heat pump, (output), to the energy required to operate the heat pump, (input). ((Ref: 49/3))

Refrigerant distributors are sized for cooling operation. What potential problem does this create for heat pump applications, and how is it solved?

The distributor nozzle, sized for refrigerant flow during the cooling cycle, may offer too much restriction during the reverse flow of the heating cycle. Heat pump distributors have a side connection between the nozzle and the internal passages, allowing refrigerant to bypass the nozzle and thus minimizing pressure loss. ((Ref: 127/3))

What is the function of a bleed resistor on a start capacitor?

The electrical resistor connected across the capacitor "bleeds" the charge from the capacitor during the run cycle to prevent arcing at the potential start relay contacts when the cycle ends. ((Ref: 155/2))

List at least five factors that must be controlled if a comfortable indoor environment is to be maintained.

The factors that must be controlled include temperature, humidity, air motion, dust, bacteria, odors, toxic gases, and ionization. ((Ref: 1/1))

Describe the advantages of using a three- stage thermostat to control a two-speed heat pump with electric auxiliary heat.

The first-stage thermostat switch controls the first stage of the heat pump compressor. The second-stage switch controls the second stage of the heat pump compressor. The third-stage switch controls the auxiliary heat. Auxiliary heat is cycled on in response to changes in the heat load in the conditioned space, rather than by outdoor thermostats set to an estimated thermal balance point. Ref: 200/4, Figure 8-10

How is a two-stage thermostat used to control a single-stage heat pump with electric auxiliary heat?

The first-stage thermostat switch controls the heat pump. The second-stage switch controls the auxiliary heat. Outdoor thermostats may be used to keep the auxiliary heat off when the ambient temperature is above the thermal balance point. Ref: 200/1

How is the cabinet of an electric furnace normally grounded?

The furnace cabinet usually is grounded to the house wiring system. Typically, a grounding lug is provided for this purpose. (Ref: 250/1)

What is the thermal balance point of a heat pump system?

The outdoor air temperature at which the output of the heat pump equals the heat loss of the structure. ((Ref: 47/2))

What will happen if the defrost termination temperature setting on the Robertshaw air/temperature defrost control is too low?

The outdoor coil will fail to defrost completely before the heat pump returns to its normal heating function. (Robertshaw 3411) (Ref: 226/2)

What is saturated vapor pressure?

The pressure exerted by a saturated vapor above its own liquid or solid, the pressure at which vapor and its liquid, or vapor and its solid, can exist in equilibrium at a given temperature. ((Ref: 10/5))

What is meant by referring to a vapor compression system as a "closed" system?

The term "closed" indicates that the system continually repeats itself without depleting the refrigerant contained within it. ((Ref: 64/2))

What is the purpose of the test mode in electronic time-temperature defrost controls?

The test mode accelerates all defrost cycle frequencies. (Ref: 237/3)

What is meant by the term synchronous motor speed?

The theoretical speed that a motor could achieve in the absence of friction. ((Ref: 116/1))

What result would you expect to observe if the Ranco E-15 control fails to end defrost after all the ice has been removed from the outdoor coil?

The unit will trip on the rapidly rising head pressure. (Ref: 232/3)

What problems occur when flash gas enters a TEV while a system is operating?

The valve operates inefficiently, the system loses capacity, and superheat increases. ((Ref: 123/1))

What is the mathematical relationship between specific volume and density?

They are reciprocals of each other. ((Ref: 11/3))

Define the working voltage rating of a capacitor.

The working voltage rating of a capacitor is the maximum voltage difference between the capacitor plates that the capacitor can withstand without arcing through the dielectric and causing the capacitor to fail. Ref: 169/2

What is a potential disadvantage of using night setback when heating a home with a heat pump?

There is an extended period of compressor off time at the beginning of setback. This period of inactivity may be as long as 2 to 4 hours, and occurs late at night when outdoor ambient temperatures are low. Restarting the compressor under these conditions results in equipment stress and presents an opportunity to slug the compressor with liquid refrigerant. Energy consumed by crankcase heat when the compressor is off will reduce the savings anticipated from setback. Ref: 196/6-1 97/1

16. How does the oil return to the compressor in a heat pump system that is equipped with a suction-line accumulator?

Through the small hole drilled in the lower portion of the U-tube. ((Ref: 137/4))

What is the function of a motor overload protector?

To de-energize the compressor if system problems cause winding temperatures to rise above an acceptable level. ((Ref: 116/5-117/1))

Why is the indoor air volume required for heat pump operation greater than the volume required for cooling-only applications?

To ensure adequate condensing of the refrigerant during the heating mode. ((Ref: 64/1))

Why is it important for electric heater packages to be installed so that air flow through the heater is in the right direction?

To ensure the proper operation of safety switches installed at the factory. (Ref: 249/2)

What is the purpose of a ladder diagram?

To isolate various electric circuits in a system, making it easier to understand the operating functions of the different switches and loads. ((Ref: 152/4))

Why are suction-line accumulators used in heat pump systems?

To prevent liquid refrigerant from entering the compressor when the system evaporator is flooded. When a heat pump changes from heating to cooling, the flooded outdoor coil would allow liquid refrigerant to reach the compressor if not protected by a accumulator. ((Ref: 137/1))

Why does the indoor coil of a heat pump need more area than the indoor coil of a cooling-only unit?

To prevent the condensing temperatures and corresponding head pressures from becoming too high during the heating cycle. ((Ref: 63/2))

What is the purpose of a point-to-point schematic wiring diagram?

To provide a detailed representation of the actual wiring of a specific system, showing and identifying every wire and connection. ((Ref: 150/2))

What is the purpose of a pictorial diagram?

To show the physical location of all components in the control cabinet. ((Ref: 149/4))

What is the typical override period for defrost controls used in multispeed heat pumps?

Up to 15 minutes. (Ref: 31/3)

How can you inspect ball-type check valves for free movement of the ball?

Valves of this type may be checked for free movement with a magnet when the system is not running. ((Ref: 136/4))

Reciprocating compressors are valved and exhibit BLANK compression ratios. By contrast, scroll compressors are ported and exhibit BLANK compression ratios.

Variable, fixed. ((Ref: 109/4-110/1))

Describe the method used to free up a sticky main valve slide.

With the system operating at normal operating pressures, rapidly energize and deenergize the reversing valve solenoid several times. Before condemning the valve, perform the same procedure after raising the system head pressure. ((Ref: 139/3))

Is it possible for parallel circuits operating with the same power supply to have different currents passing through each branch?

Yes ((Ref: 149/1))

If you must replace a defective start capacitor, can the replacement capacitor have a different microfarad value than the original?

Yes. A replacement start capacitor with a slightly higher microfarad value than the original may be used without incurring problems. A replacement with a lower microfarad value than the original should never be used. Ref: 172/2 It is best to stay within 10 percent of the original. If you must replace it with a lower rated capacitor, do so within the 10% range.

On a new or repaired heat pump unit, what steps should you take to check for contamination?

You should check the moisture indicator, if available, the acid content, the system pressure drop, and the pressure drop across the filter-drier. ((Ref: 132/4))

If a pressure-activated defrost control fails to initiate during the first days of the heating season, what is a likely problem that should be checked?

You should check the pressure tube that senses atmospheric pressure for insects, spider sacs, or other restrictions. (Ref: 216/8-217/1)

20. When using the "touch test" chart to check the operation of a reversing valve, what are the normal conditions for each of the following in the cooling mode? a. Discharge tube from compressor b. Suction tube to compressor c. Tube to inside coil d. Tube to outside coil e. Left pilot capillary tube f. Right pilot capillary tube

a. Hot b. Cool c. Cool d. Hot e. Temperature of valve body f. Temperature of valve body ((Ref: 142/Table 5-4))