ESCO Air Conditioning Exam Flashcards

Questions and Answers

Heat which causes a change in temperature of a substance is called?

Sensible heat

Heat added to a substance without a rise in temperature is called?

Latent heat

Heat added to the refrigerant in a vapor state after the evaporation process is called?

Superheat

Scroll compressor move refrigerant by?

Involute Spirals Signup and view all the answers

The movement of heat by way of fluid is called?

Convection Signup and view all the answers

The movement of heat by direct contact is?

Conduction Signup and view all the answers

The standard unit for measuring the quantity of heat in a substance is?

BTUs Signup and view all the answers

Refrigerant gives up heat when?

It condenses Signup and view all the answers

Why must refrigerant in the suction line be slightly warmer than the saturation temperature?

Prevent liquid slugging of the compressor Signup and view all the answers

The state of the refrigerant in the suction line should be?

Low pressure / Low temperature vapor Signup and view all the answers

The state of the refrigerant entering the condenser is?

High pressure / Highly superheated vapor Signup and view all the answers

The evaporator?

Transfers heat from the refrigerated space to the refrigerant Signup and view all the answers

Which of the following is not a thermodynamic property of refrigerants?

Flammability Signup and view all the answers

The sequential order of steps in the vapor compression process are?

Compression, Condensation, Expansion, Vaporization Signup and view all the answers

If a 30 pound cylinder of reclaimed R-410A refrigerant has been stored overnight at 70°, the pressure in the cylinder should be approximately?

201 psig Signup and view all the answers

Fan airflow pressures are usually measured in?

Inches of water column Signup and view all the answers

0 pounds per square inch absolute is?

A pressure which cannot be further reduced Signup and view all the answers

0 pounds per square inch gauge is?

The same as atmospheric pressure Signup and view all the answers

The temperature at which moisture will start to condense from the air is called?

Dew point temperature Signup and view all the answers

A compound pressure gauge measures?

Pressure and vacuum Signup and view all the answers

Mechanical shaft seal is necessary on a?

Open drive compressor Signup and view all the answers

Liquid slugging is?

Liquid refrigerant in the compressor clearance space Signup and view all the answers

The clearance space in a reciprocating compressor?

Has an effect on compressor capacity Signup and view all the answers

Which of the following types of air conditioning compressor is most energy-efficient?

Scroll Signup and view all the answers

Which of the following represent the right order for the functions of a condenser?

De-superheat, Condenses, Subcools Signup and view all the answers

Refrigerant R-134A vapor enters the condenser at 124 psig, 100°F; it leaves as a liquid from the condenser subcooled 20°F and the pressure will be approximately?

87 psig Signup and view all the answers

There are three basic types of condensers, air-cooled, water-cooled and the _____________ cooled.

Evaporative Signup and view all the answers

10 pounds of refrigerant passing through a water-cooled condenser will lose 20 BTUs of heat per pound. If 10 pounds of water passes through the condenser with an entering temperature of 80°F, the temperature of the water leaving the condenser is?

100°F Signup and view all the answers

The heat removed from the refrigerant by the condenser is?

Both sensible and latent heat Signup and view all the answers

An energy recovery ventilator is?

An air to air heat exchanger to recover heat Signup and view all the answers

When testing the efficiency of an air-cooled condenser, the refrigerant condensing temperature should be approximately ________ higher than the entering air temperature.

30°F Signup and view all the answers

When testing the efficiency of a water-cooled condenser, the refrigerant condensing temperature should be approximately _________ higher than the leaving water temperature.

10°F Signup and view all the answers

The first function a condenser must perform is to?

De-superheat Signup and view all the answers

A thermostatic expansion valve is designed to maintain?

Constant evaporator superheat Signup and view all the answers

The automatic expansion valve is designed to maintain?

Constant evaporator pressure Signup and view all the answers

The thermostatic expansion valve has three operating pressures?

Evaporator pressure, Spring pressure, and Sensor bulb pressure Signup and view all the answers

When mounting a thermostatic expansion valve sensor bulb, which of the following is not true?

It must be installed lower than the valve body Signup and view all the answers

In an air conditioning system that uses a thermostatic expansion valve, the temperature of the evaporator outlet will usually be?

Warmer than the evaporator inlet Signup and view all the answers

An automatic expansion valve is best suited?

When the system load remains fairly constant Signup and view all the answers

Which of the following is not true of a capillary tube metering device?

They maintain a constant evaporator temperature Signup and view all the answers

A decrease in superheat causes the thermostatic expansion valve to begin to?

Close Signup and view all the answers

A rise in evaporator pressure causes the automatic expansion valve to begin to?

Close Signup and view all the answers

A thermal electric expansion valve is controlled by?

NTC thermistor Signup and view all the answers

In a direct expansion evaporator system, the refrigerant enters the evaporator as?

A mixture of liquid with some 'flash-gas' Signup and view all the answers

Which of the following is the most important consideration in the selection of an evaporator coil?

Match the coil to the condensing unit and the latent/sensible loads Signup and view all the answers

In the evaporator?

Latent heat is transferred from the refrigerated space to the refrigerant Signup and view all the answers

A liquid line filter-drier should be placed between the?

Condenser and the Metering device Signup and view all the answers

The only way to minimize flash gas is by?

Sub-cooling the liquid refrigerant entering the metering device closer to the evaporator temperature Signup and view all the answers

A liquid receiver is used to?

Store liquid refrigerant Signup and view all the answers

An accumulator is used to?

Prevent liquid refrigerant from reaching the compressor Signup and view all the answers

A sight glass would be normally located?

In the liquid line before the metering device Signup and view all the answers

Bubbles in a sight glass would be an indication of?

TXV with an excessive superheat setting Signup and view all the answers

The oil separator is installed in the?

Discharge Line Signup and view all the answers

Which of the following is true of a solenoid valve in a pump down system?

It's located before the metering device Signup and view all the answers

The purpose of an evaporator pressure regulating valve is to?

Prevent evaporator pressure from falling below a set limit Signup and view all the answers

A liquid to suction heat exchanger is often used to?

Increase liquid subcooling Signup and view all the answers

The oil pressure safety switch is operated by ___________.

The difference between crankcase pressure and oil pump pressure Signup and view all the answers

A low pressure cutoff switch is used to?

Establish a minimum operating pressure in the evaporator Signup and view all the answers

A partially iced-over evaporator can be caused by?

An undercharge Signup and view all the answers

_________ can be used for leak detection with all high-pressure refrigerants.

Soap bubbles Signup and view all the answers

The flow rate of a TXV used in R-410A systems compared to R-22 systems is?

Approximately 15% greater Signup and view all the answers

When using an electronic leak detector, the sensor probe?

Should be moved at approximately 1 inch for every two seconds Signup and view all the answers

Moisture in a refrigeration system will cause?

Compressor failure Signup and view all the answers

In order to remove as much moisture as possible from a system?

Triple evacuate the system to 500 microns with a deep vacuum pump Signup and view all the answers

What type of gauge is used to measure microns?

An electronic vacuum gauge Signup and view all the answers

Water will vaporize at ________ temperature in a 28 in hg vacuum.

10°F Signup and view all the answers

After a system has been opened and the compressor changed, the service technician must?

Replace the filter dryer, leak check, evacuate, and charge Signup and view all the answers

Back seating a two-way service valve results in?

Open service port with normal system flow Signup and view all the answers

The R-410A compound gauge reads 124 psig in the suction line; the temperature at the condensing unit is 54°F. What is the operating system superheat?

12°F Signup and view all the answers

When topping off an operating system containing a blended refrigerant?

Introduce the refrigerant as a liquid into the low side using the throttling valve Signup and view all the answers

A partially clogged capillary tube can cause?

A starved evaporator Signup and view all the answers

The R-134A for a high-pressure gauge reads 146 psig in the liquid line; the temperature at the condensing unit is 95°F. What is the operating system subcooling?

15°F Signup and view all the answers

An overcharge of refrigerant will cause?

Increased head pressure Signup and view all the answers

A customer complains that their air conditioning system is running constantly, but not cooling enough. The suction line is very cold and the compressor is sweating. The most likely cause is?

A restriction of the return air or a dirty evaporator Signup and view all the answers

A drain trap should be installed on a split system when the?

Air handler drain is on the negative air side Signup and view all the answers

A customer reports that the residential split system had a compressor replaced last week by another service company. Now the unit is not cooling properly. When you arrive and inspect the unit, you find that the evaporator seems to be starved for refrigerant. On examining the condensing unit, you find that the liquid line is sweating where it leaves the dryer. This is most likely the result of?

Debris from the burned-out compressor has clogged the dryer Signup and view all the answers

What is the generally accepted range for evaporator airflow in CFM's per ton of residential air conditioning?

350 to 450 Signup and view all the answers

The temperature rise method for determining airflow is?

CFM = BTU / (1.08 x delta T) Signup and view all the answers

What is the recommended residential indoor relative humidity for summer?

50% Signup and view all the answers

In an inefficient compressor, it is usually indicated by head pressure and suction pressure.

Higher than normal / Lower than normal Signup and view all the answers

Which of the following is not a symptom of a hermetic system that is low on refrigerant?

High head pressure Signup and view all the answers

Frost on the suction line indicates?

That its temperature is below the dew point and it's below 32 degrees Signup and view all the answers

An increase in head pressure causes ___ refrigerant to flow through a capillary tube.

More Signup and view all the answers

With an automatic expansion valve, an increase in evaporator load will cause the?

Automatic expansion valve to close Signup and view all the answers

When a TEV or capillary tube is used as a metering device, a low refrigerant charge will cause?

Low head pressure Signup and view all the answers

What is the maximum operating pressure setting for an acetylene torch?

15 psig Signup and view all the answers

When connecting copper to steel, the recommended brazing filler alloy is?

45% silver alloy Signup and view all the answers

Solid contaminants such as sludge and carbon from a severe hermetic compressor motor burnout are best removed?

By flushing the system and then installing filter dryers in both the liquid and suction lines Signup and view all the answers

If the cutoff play is removed from the blower assembly, how will this affect blower performance?

It would reduce airflow Signup and view all the answers

At a residential service call with no cooling complaint, the service technician finds the unit to be completely out of refrigerant. The technician decides to use a trace amount of refrigerant and ___ in order to pressurize the system.

Inert gas Signup and view all the answers

A technician has found an air conditioning system with a leak in the liquid line. After the line is repaired, the system is evacuated and properly recharged. When the system restarted, the compressor is noisy and running hot. The most probable cause of the noise is?

Low oil in the system Signup and view all the answers

An air conditioning system that is oversized can cause?

Inefficient dehumidification of the conditioned space Signup and view all the answers

While troubleshooting a residential split system, the service technician finds slow operating pressures and low system amperage draw. This could be an indication of?

Low airflow across the evaporator Signup and view all the answers

Air or other non-condensable gases in a capillary tube air conditioning system will cause the symptoms?

High suction pressure and high discharge pressure Signup and view all the answers

A refrigerant overcharge in a capillary tube air conditioning system will cause the symptoms?

High suction pressure and high discharge pressure Signup and view all the answers

A compressor that has a broken reed valve will cause the symptoms?

High suction pressure and low discharge pressure Signup and view all the answers

A low refrigerant charge in an air conditioning system will cause the symptoms?

Low suction pressure and low discharge pressure Signup and view all the answers

A TEV sensing bulb which becomes detached from the suction line will cause the symptoms?

High suction pressure and lower than normal discharge pressure Signup and view all the answers

A faulty condenser fan motor on an air conditioning system will cause the symptoms?

High suction pressure and high discharge pressure Signup and view all the answers

A dirty evaporator in an air conditioning system will cause the symptoms?

Low suction pressure and low discharge pressure Signup and view all the answers

Study Notes

Heat Transfer Concepts

Sensible heat causes a temperature change in a substance.
Latent heat is added to a substance without a temperature rise.
Superheat refers to heat added to refrigerant in vapor state after evaporation.

Refrigeration and Compression

Scroll compressors use involute spirals to move refrigerant.
Refrigerants condense when they give up heat.
Refrigerant states: suction line should have low pressure/low temperature vapor; entering condenser should be high pressure/highly superheated vapor.

Thermodynamic Principles

Sensible and latent heat are involved in heat removal by the condenser.
Dew point temperature is when moisture begins to condense from air.

Refrigerant and Pressure Measurements

Standard heat measurement unit is BTUs.
Compound pressure gauges measure both pressure and vacuum.
0 psi absolute is the lowest pressure achievable; 0 psi gauge equals atmospheric pressure.

Component Functions in AC Systems

Evaporators transfer heat from refrigerated spaces to refrigerants.
An accumulator prevents liquid refrigerant from reaching the compressor.
The first condenser function is to de-superheat refrigerant.

Valving and Expansion Mechanisms

Thermostatic expansion valves (TXV) maintain constant evaporator superheat.
Automatic expansion valves ensure constant evaporator pressure.
A decrease in superheat causes the TXV to close; a rise in evaporator pressure makes the automatic expansion valve close.

System Performance Indicators

High suction pressure with low discharge pressure can indicate a broken reed valve.
Low refrigerant charges result in low suction and discharge pressures.
Frost on the suction line indicates it is below dew point and below 32°F.

Maintenance and Troubleshooting

A liquid line filter-drier should be placed between the condenser and metering device for system protection.
Performance issues like constant running without cooling may signify a dirty evaporator or airflow restrictions.
Service technicians should triple evacuate a system to an extreme vacuum to remove moisture.

Efficiency and Operation

Evaporator airflow should range from 350 to 450 CFM per ton of cooling.
Using improper refrigerants, or overcharging can raise head pressure and lead to system inefficiency.
Inert gases are used for system pressurization when introducing refrigerant.

System Safety Measures

Oil pressure safety switches monitor crankcase and oil pump pressure differences.
To detect leaks, soap bubbles can be effective for high-pressure refrigerants.

Special Situations and Considerations

A dirty evaporator indicates low suction and discharge pressures, possibly resulting from restricted airflow.
In oversized systems, a common issue is inefficient dehumidification in conditioned spaces.
If debris clogs the dryer after a compressor burn-out, system flushing and new filter dryers are necessary for restoring proper function.

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Prepare for your ESCO Air Conditioning Exam with these flashcards covering essential concepts such as sensible heat, latent heat, and superheat. This quiz provides a focused review of key terms and definitions necessary for mastering air conditioning principles.