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 retired. When the system is started, the compressor is noisy and running hot. The most probable cause of the
Lower oil in the system
The standard unit for measuring the quantity of heat in a substance is....
The British Thermal Unit (Btu)
Zero psia (pounds per square inch absolute) is....
Pressure which cannot be further reduced
A liquid receiver is used to....
Store liquid refrigerant
A low refrigerant charge in an air conditioning system will cause these symptoms...
Low suction pressure and low discharge pressure
A TXV sensing bulb which becomes detached from the suction line will cause these symptoms....
High suction pressure and higher than normal discharge pressure
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
The oil pressure safety switch is operated by....
The difference between crankcase pressure and oil pressure
The sequential order of steps in the vapor - compression process are....
Compression, condensation, expansion, vaporization
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 clearance space in a reciprocating compressor....
Has an effect on compressor capacity
___________ can be used for leak detection with all high pressure refrigerants.
Soap/bubble solution
A thermal electric (solid state) expansion valve is controlled by....
NTC thermistor
The temperature at which moisture will start to condense from the air is called....
Dew point temperature
Which of the following is NOT a symptom of a hermetic system that is low on refrigerant?
High head pressure
In the evaporator.....
Latent heat is transferred from the refrigerated space to the refrigerant
In a direct expansion (DX) evaporator system, the refrigerant enters the evaporator as...
A mixture of liquid with some "flash gas".
The flow rate of a TXV used in R410a system as compared to R22 systems is....
Approximately 15% less
If the evaporator pressure does not change when heat is added or removed from the thermostatic expansion bulb, the problem may be...
A faulty bulb or power head assembly
A partially clogged capillary tube can cause....
A starved evaporator
A liquid-to-suction heat exchanger is other used to...
Increase liquid sub cooling
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 a trace amount of refrigerant and _____________ in order to pressurize the system.
An inert gas
A drain trap should be installed on a split system when the....
Air handler drain is on the negative air side
When testing the efficiency of a water cooled condenser, the refrigerant condensing temperate should be approximately ____________ higher than the leaving water temperature
10 degrees F
A liquid line filter drier should be replaced between the...
Condenser and the metering device
A low pressure cut off switch is used to....
Establish a minimum operating pressure in the evaporator
The movement of heat by direct contact is called....
Conduction
An increase in head pressure causes ___________ refrigerant to flow through the capillary tube.
More
Which of the following represent the right order of the functions of a condenser?
De-superheats, condenses, sub cools
The movement of heat by the way of fluid (or air) is called....
Convection
An overcharge of refrigerant will cause....
Increased head pressure
The temperature rise method for determining air fflow is.....
CFM = BTU / (1.08 x delta-T)
Which of the following is TRUE of a solenoid valve in a pump down system?
It is located before the metering device
A sight glass would normally be located...
In the liquid line, before the metering device
Air and other non-condensable gasses in a capillary tube air conditioning system will cause these symptoms....
High suction pressure and high discharge pressure
Bubbles in a sight glass could be an indication of....
Low compressor capacity
An accumulator is used to....
Prevent liquid refrigerant from reaching the compressor
Back seating a two way service valve results in....
Open service port with normal system flow
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
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 sub cooling?
15 degrees F
Refrigerant R-134a vapor enters the condenser at 124 psig, 100 degrees F. It leaves as a liquid from the condenser sub cooled 20 degrees F and the pressure with be approximately.....
124 psig
When mounting a thermostatic expansion valve senor bulb, which of the following is not true?
It must be installed lover than the valve body
A customer reports that their residential split system has a compressor replaced last week by another service company. The the unit is not cooling properly. When you arrive and inspect the unit, you find that the evaporator seems to be starved for refrige
Debris from the burned out compressor has clogged the drier
Which of the following is NOT true of a capillary tube metering device?
They maintain a constant evaporator temperature
Which of the following is NOT a thermodynamic property of refrigerants?
Flammability
The automatic expansion valve is designed to maintain....
Constant evaporator pressure
A refrigerant overcharge in a capillary tube air conditioning system will cause these symptoms.....
High suction pressure and high discharge pressure
When a TEV or a capillary tube is used as a metering device, a low refrigerant charge will cause....
Low head pressure
Moisture in a refrigeration system can cause.....
Compressor failure
How does a TXV in an operating air conditioning unit react when the bulb is not attached to the outlet or suction line and hanging in the air?
The valve will stay open and not maintain proper superheat