Hvac Excellence A/C

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

sensible heat

Heat added to a substance without a rise in temperature; (ex: liquid refrigerant to gas) this process is called?

Latent heat of vaporization

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

Superheat

a scroll compressor move refrigerant by means of

Involute spirals

The movement of heat by way of fluid (or air) is called

Convection

The movement of heat through a solid object is called

Conduction

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

The British Thermal Unit (BTU)

A refrigerant gives up heat when

It condenses

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

Prevent liquid slugging of the compressor

The state of the refrigerant in the suction line should be

Low pressure/Low temperature vapor

The state of the refrigerant entering the condenser

High pressure/Highly superheated vapor

The evaporator

transfers heat from the refrigerated space to the refrigerant

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

Flammability

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

Compression, Condensation, Expansion, Vaporization

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

201 psig

Fan airflow pressures are usually measured in

Inches of water column (WC)

Zero psia (pounds per square inch absolute) is

A pressure which cannot be further reduced

Zero psig (pounds per square inch gauge) is

The same as atmospheric pressure

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

Dew point temperature

A compound pressure gauge measures

Pressure and vacuum

A mechanical shaft seal is necessary on a

Hermetic rotary compressor

Liquid slugging is

Liquid refrigerant in the compressor clearance space

The clearance space in a reciprocating compressor

Has an effect on compressor capacity

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

Scroll

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

De-superheats, condenses, sub-cools

Refrigerant R-134a vapor enters the condenser at 124 psig, 100 F. It leaves as a liquid from the condenser sub-cooled 20 F and the pressure will be approximately

87 psig

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

Evaporative

10lbs. of refrigerant passing through a water cooled condenser will lose 20 Btu's of heat per lb. If 10 lbs. of water passes through the condenser with an entering temperature of 80 F. The temperature of the water leaving the condenser is

100 F

The heat removed from the refrigerant by the condenser is

Both sensible and latent heat

A Energy Recovery Ventilator is

An air to air heat-exchanger to recover heat

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

30 F

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

10 F

The first function a condenser must perform is to ____ the refrigerant before condensing can occur.

De-superheat

A thermostatic expansion valve is designed to maintain

Constant evaporator superheat

The automatic expansion valve is designed to maintain

Constant evaporator pressure

The thermostatic expansion valve has three operating pressures

Evaporator pressure, spring pressure, & sensor bulb pressure

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

It must be installed lower than the valve body

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

An automatic expansion valve is best suited

When the system load remains fairly constant

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

They maintain a constant evaporator temperature

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

Close

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

Close

A thermal-electric (solid state) expansion valve is controlled by

NTC thermistor

In a direct expansion (DX) evaporator system, the refrigerant enters the evaporator as

A mixture of liquid with some "flash-gas"

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

In the evaporator

Latent heat is transferred from the refrigerant space to the refrigerant

A liquid line filter-drier should be placed between the

Condenser and the metering device

The only way to minimize flash gas is by

Sub-cooling the liquid refrigerant entering the metering device closer to the evaporator temperature

A liquid receiver is used to

Store liquid refrigerant

An accumulator is used to

Prevent liquid refrigerant from reaching the compressor

A sight glass would normally be located

In the liquid line, before the metering device

Bubbles in a sight glass could be an indication of

A refrigerant blend with a high temperature glide

The oil separator is installed in the

Discharge line

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

It is located before the metering device

The purpose of an evaporator pressure regulating valve (EPR) is to

Prevent evaporator pressure from falling below a set limit

A liquid-to-suction heat exchanger is often used to

Increase liquid sub-cooling

The oil pressure safety switch is operated by

The difference between crankcase pressure and oil pressure

A low pressure cut-off switch is used to

Establish a minimum operating pressure in the evaporator

A partially iced over evaporator can be caused by

An undercharge

____ can be used for leak detection with ALL high pressure refrigerants

Soap bubbles

The flow rate of a TXV used in R-410a systems as compared to R22 systems is

Approximately 15% less

When using an electronic leak detector, the sensor probe

Should be moved at approximately 1 inch every two seconds

Moisture in a refrigerant system will cause

Compressor failure

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

Triple evacuate the system to 500 microns with a deep vacuum pump

What type of gauge is used to measure microns?

An electronic vacuum gauge

Water will vaporize at ______ temperature in a 28 in Hg vacuum

100 F

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

Replace the filter drier, leak check, evacuate, and charge

Back seating a two way service valve results in

Closed service port with normal system flow

The R410a compound gauge reads 124 psig and the suction line temperature at the condensing unit is 54 degrees F, What is the operating superheat?

12 degrees F

When topping off an operating system containing a blended refrigerant

Introduce the refrigerant as a liquid into the low side using a throttling valve

A partially clogged capillary tube can cause

A starved evaporator

The R134a high pressure gauge reads 146 psig and the liquid line temperature at the condensing unit is 95 degrees F. What is the operating system subcooling?

15 degrees F

An overcharge of refrigerant will cause

Increased head pressure

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

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

Air handler drain is on the negative air side

A customer reports that their 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 drier. This is most likely the result of

Debris from the burned out compressor has clogged the drier

What is the generally accepted range for evaporator air flow in CFMs per ton of residential air conditioning?

350-450

The temperature rise method for determining air flow is

CFM=BTU/(1.08xDelta T)

What is the recommended residential indoor relative humidity for summer?

50%

An inefficient compressor is usually indicated by _____ head pressure and _____ suction pressure

Lower than normal/Higher than normal

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

High head pressure

Frost on the suction line indicates

that its temperature is below the dew point and below 32 F

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

more

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

Automatic expansion valve to close

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

Low head pressure

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

15 psig

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

45 percent silver alloy

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 / driers in both the liquid and suction lines

If the cut-off plate is removed from a blower assembly, how could this effect blower performance?

It would reduce air flow

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

An inert gas

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 is started, the compressor is noisy and running hot. The most probable cause of the noise is

Low oil in the system

An air conditioning system that is oversized can cause

Inefficient dehumidification of the conditioned space

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

Low airflow across the evaporator

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

High suction pressure and high discharge pressure

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

High suction pressure and high discharge pressure

A compressor that has a broken reed valve will cause these symptoms

High suction pressure and low discharge pressure

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

Low suction pressure and low discharge pressure

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

High suction pressure and higher than normal discharge pressure

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

High suction pressure and a high discharge pressure

A dirty evaporator on an air conditioning system will cause these symptoms

Low suction pressure and low discharge pressure