UNIT 29 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX
29-1) Why are systems with fixed restriction metering devices critical to charge?
29-2) How does an overcharge of refrigerant affect system efficiency?
29-3) Why must refrigerants that fractionate, such as R-410a, be charged as a liquid?
29-4) How does an undercharge affect the superheat of a fixed restriction system?
29-5) How does an overcharge affect the superheat of a fixed restriction system?
29-6) How does an undercharge affect the subcooling of a thermostatic expansion valve
system?
29-7) How does an overcharge affect the subcooling of a thermostatic expansion valve
system?
29-8) What is the best method for charging a large system that holds 50 pounds of
refrigerant?
29-9) What is the best method to charging a small appliance that holds less than a pound
of refrigerant?
29-10) Using Figure 29-22, what would be the proper superheat for a system with an
ambient temperature of 95oF and a return air wet bulb of 70°F?
29-11) Using the information in question 10, you measure a suction pressure of 130 psig
for an R-410A system. What should the suction line temperature be?
29-12) Using the information from questions 10 & 11, what charge adjustment should be
made if the suction line measures 55°F?
29-13) Using Figure 29-28, what would be the proper subcooling for a system with an
ambient temperature of 115oF and a return air wet bulb of 62°F?
29-14) Using the information from question 13, what should the liquid line temperature
be if the liquid pressure is 293 psig for an R-22 system?
29-15) Using the information from questions 13 and 14, what charge adjustment needs to
be made if the liquid line temperature is 110°F.?
29-16) Why should a system be leak tested after it has been repaired before it is charged?
29-17) Outline the procedure for adding oil to a semi-hermetic compressor without
opening the compressor.
29-18) How often should the refrigeration oil in a compressor be changed?
29-19) Using Figure 29-30, what should the liquid line temperature be for a model
10ACB30 unit operating in an ambient temperature of 97°F?
29-20) Using the information from question 19, what charge adjustment needs to be
made if the liquid line temperature is 110°F?
29-21) Using Figure 29-18, the suction pressure is 140 psig, the liquid pressure is 370
psig, and the ambient temperature is 105°F. What charge adjustment needs to be
made?
29-22) Using Figure 29-18, the suction pressure is 155 psig, the liquid pressure is 360
psig, and the ambient temperature is 95°F. What charge adjustment needs to be
made?
29-23) List the variables that affect system pressures.
Outdoor ambient temperature for air-cooled units
Condenser airflow for air-cooled units
29-24) Give an example of a condition that can make a system appear overcharged even
though the charge is correct.
29-25) Give an example of a condition that can make a system appear undercharged even
though the charge is correct.
29-26) What is the standard AHRI design condition used for rating unitary air
conditioning equipment?
29-27) Who is the most reliable source of information regarding the charge for any
particular piece of equipment?
29-28) A new split system air conditioning system is being installed. The actual line
length is 48 feet. The factory charge for the condensing unit is 94 ounces. The
installation instructions state that the factory charge assumes a line length of 20 feet
and gives the per foot adjustment as 0.6 ounces per foot. How much refrigerant
should be added to the system after the lines and coil have been evacuated?
29-29) The compressor in an existing split system air conditioning system is being
replaced. The actual line length is 35 feet. The factory charge for the condensing unit
is 100 ounces. The installation instructions state that the factory charge assumes a line
length of 15 feet and gives the per foot adjustment as 0.6 ounces per foot. How much
refrigerant should be added to the system after the system has been evacuated?