HVAC Excellence
When testing efficiency of a water cooled condenser, the refrigerant condensing temperature should be approximately _________________ higher than the leaving water temperature.
10'F
10lbs. Of refrigerant passing through a water cooled condenser will lose 20 BTU of heat per lb. if 10lbs. Of water passes through the condenser with an entering temperature of 80'F. The temperature of the water leaving the condenser is.
100'F
Water will vaporize at _______ what temperature in a 28 in Hg vacuum
100'F
The R410A compound gauge reads 124 psig and the suction line temperature at the condensing unit is 54 degrees F. What is the operating system superheat?
12 ' F
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.
124 psig
What is the maximum operating pressure setting for an acetylene torch?
15 psig
The R134A high pressure gauge reads 146 psig and the liquid line temperature at the condensing unit at 95 degrees F what is the operating sub cooling?
15'F
If a 30 pound container of R-410A refrigerant has been stored over night at 70'F, the pressure in the cylinder should be approximately.
201 psig
When testing the efficiency of an air cooled condenser, the refrigerant condensing temperature should be no more than ___________ higher than the entering air temperature.
30'F
What is generally accepted range for evaporator air flow in CDM's per ton of residential air conditioning?
350 to 450
When connecting copper to steel the recommended brazing filler alloy is a
45 % silver alloy
What is the recommended residential in door relative humidity for summer?
50%
In a direct expansion (DX) evaporator system, the refrigerant enters the evaporator as.
A mixture of liquid with some "FLASH GAS"
Zero psia (pounds per square inch absolute) is.
A pressure which cannot be further reduced
A partially clogged capillary tube metering device can cause
A starved evaporator
A drain trap should be installed on a split system when the
Air handler drain is on the negative side
An energy recovery ventilator is.
An air to air heat exchanger to recover heat
What kind of gauge is used to measure microns.
An electronic vacuum gauge
A partially iced over evaporator can be caused by.
An undercharge
The flow rate of a TXV used in R410A systems as compared to R22 system is.
Approximately 15% lower
With an automatic expansion valve an increase in evaporator load will cause the
Automatic expansion valve to close
The heat removed from the refrigerant by the condenser is.
Both sensible and latent heat
The standard unit for measuring the QUANTITY of heat in a substance is (intensity would be temp)
British thermal unit
Solid contaminants such as sludge and carbon from a severe hermetic compressor motor burn out are best removed
By flushing the system and then Installing filter/driers in both the liquid and suction lines.
The temperature rise method for determining air flow is.
CFM=BTU / (1.08X Delta T)
Which of the following types of air conditioning compressors is most energy efficient
Centrifugal ( BTU/Kilo watts )
A decrease in superheat causes the thermostatic expansion valve begins to.
Close
A rise in evaporator pressure causes the automatic expansion valve to begin to.
Close
Back seating a two way service valve results In
Closed service port with normal system flow
The sequential order of stepson the vapor-compression process are.
Compression, condensation, expansion, vaporization
Moisture in the refrigeration system will cause
Compressor failure
A liquid line filter drier should be placed between the.
Condenser and metering device
The movement of heat through a solid object is called.
Conduction
The automatic expansion valve is designed to maintain.
Constant evaporator pressure.
A thermostatic expansion valve is designed to maintain.
Constant evaporator superheat
The movement of heat by way of fluid or is called air or gas.
Convection
Which of the following can NOT be used as a low ambient temperature control?
Crankcase regulating valves
The first function a condenser must perform is to ____________ the refrigerant before condensing can occur.
De-superheat
Which of the following represents the right order for the functions of a condenser.
De-superheats , condenses , sub-cools
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 of 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
The temperature at which moisture will start to condense from the air is called.
Dew point temperature
The oil separator is installed in the
Discharge line
A low pressure cut-off switch is used to. (and is also called loss of charge switch.)
Establish a minimum operating pressure in the evaporator.
There are three basic types of condensers, the air cooled, the water cooled and the BLANK cooled.
Evaporative
The thermostatic expansion valve has three operating pressure.
Evaporator pressure, spring pressure & sensing bulb pressure.
Which of the following is not a thermodynamic property of refrigerant.
Flammability
The clearance space in a reciprocating compressor.
Has no effect on compressor capacity
Which is NOT a symptom of a hermetic system that is low on refrigerant
High head pressure
The state of the refrigerant entering the condenser is.
High pressure / Highly superheated vapor
A refrigerant overcharge in a capillary Tube air conditioning system will cause the symptoms
High suction pressure and high discharge pressure
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 TEV sensing bulb which becomes detached from the suction line will cause these symptoms
High suction pressure and higher than normal discharge pressure
A compressor that has broken reed valve will cause these symptoms.
High suction pressure and low discharge pressure
A sight glass would normally be located.
In the liquid line, before the metering device.
Fan airflow pressures are usually measured in.
Inches of water column (WC)
A liquid-to-suction heat exchanger is often used to
Increase liquid subcooling
An overcharge of refrigerant will cause
Increased head pressure
An air conditioning system that is oversized can cause
Inefficient dehumidification of the conditioned space
It is desirable for refrigerant in the suction line to be slightly superheated in order to.
Insure liquid refrigerant does not enter the compressor
When topping off an operating system containing a blend refrigerant.
Introduce the refrigerant as a liquid into the low side using a throttling valve
A scroll compressor moves refrigerant by means of.
Involute spirals
A refrigerant gives up heat when it.
It condenses
Which of the following is TRUE of a solenoid valve in a pump down system?
It is located before the metering device
When mounting a thermostatic expansion valve sensor bulb, which of the following is NOT true?
It must be installed lower than the valve body
Is the cut-off plate is removed from a blower assembly how would this effect blower performance?
It would reduce air flow
Heat added to a substance without a rise in temperature; (example: liquid refrigerant to gas) this process is called?
Latent heat
In the evaporator
Latent heat is transferred from the refrigerated space to the refrigerant.
Liquid slugging is.
Liquid refrigerant in the compressor clearance space
Bubbles in the sight glass could be an indication of.
Low compressor capacity
When a TEV Or capillary tube is used as a metering device a low refrigerant charge will cause
Low head pressure
A technician has found an air conditioning system with a leak in the liquid line after the line is repaired the system 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
The state of the refrigerants in the suction line should be.
Low pressure / Low temperature vapor
While trouble shooting a residential split system the service technician finds low operating pressure and low system amperage draw this could be an indication of
Low refrigerant across the evaporator
A low refrigerant charge in a air conditioning system will cause these symptoms
Low suction pressure and low discharge pressure
An inefficient compressor is usually indicated by ________ head pressure and _______ suction pressure.
Lower than normal/higher than normal
An increase in head pressure causes __________ refrigerant to flow through the capillary tube.
More
A thermal-electric (solid state) expansion valve is controlled by.
NTC thermistor
A mechanical shaft seal is necessary on a
Open drive compressor / external force
A compound pressure gauge measures
Pressure and vacuum
The purpose of an evaporator pressure regulating valve (EPT) is to.
Prevent evaporator pressure from falling below a set limit.
An accumulator is used to.
Prevent liquid refrigerant from reaching the compressor
Why must refrigerant in the suction line be slightly warmer than the saturation temperature?
Prevent liquid slugging of the compressor
After a system has been opened and the compressor changed, the service technician must.
Replace the filter drier, leak check, evacuate, and charge
When using an electronic leak detector the sensing probe.
Should be moved at approximately 1 inch every second.
What can be used for leak detection with ALL high pressure refrigerants
Soap bubbles
A liquid receiver is used to.
Store liquid refrigerant
The only way to minimize flash gas is by
Sub-cooling the liquid refrigerant entering the metering device closer to the evaporator temperature.
Heat added to the refrigerant in a vapor state after the evaporator process is called.
Superheat
Frost on the suction line indicates
That the temperature is below the dew point and below 32°F .
The oil pressure safety switch is operated by
The difference between crankcase pressure and oil pressure
Before a vapor / compression system is opened for service
The refrigerant must be recovered using approved equipment
Zero psig ( pounds per square inch gauge) is.
The same as atmospheric pressure
Which of the following is NOT true of a capillary tube metering device?
They maintain a constant evaporator temperature
The evaporator.
Transfers heat from the refrigerated space to the refrigerant
In order to remove as much moisture as possible from a system.
Triple evacuate the system to 500 microns with a deep vacuum pump
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 / down flow , constant pressure valve.
When the system load remains fairly constant
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.
low refrigerant charge.
Heat which causes a change in temperature of a substance is called.
sensible heat.
