Chapter 29
An R-22 system operating with a liquid pressure of 226 psig (110 degrees saturation temperature). The specified system subcooling is 5 degrees Fahrenheit. The liquid line temperature should be:
105 degrees Fahrenheit
Which of the following measures is the standard airflow across an air-conditioning coil?
400 CFM per ton
An air conditioning system charged with R-410a is operating with a suction pressure of 130 psig which equates to a 45 degree Fahrenheit saturation temperature. If the manufacturer calls for a 15 degree Fahrenheit superheat, what should the suction line temperature be?
45 deg F + 15 deg F = 60 deg F suction line temperature
The compressor in an existing split system is being replaced. The system has a 35 ft line set. The factory charge for the condensing unit is 80 oz. The installation instructions state that the factory charge assumes a line length of 15 ft and gives the per foot adjustment as 0.6 oz per ft. How much refrigerant should be added to the system after the system has been evacuated?
80 oz + ((35-15) x 0.6 oz) = 92 oz
The standard AHRI "A" design condition used for rating unitary air conditioning equipment is...
95 degrees Fahrenheit outdoor ambient temperature, 80 degrees Fahrenheit dry bulb, 68 degrees Fahrenheit wet bulb indoor temperature
In general, a system that is undercharged will have...
A low subcooling and a high superheat
Can zeotropes be metered in the low side with the unit operating?
Yes, by slightly cracking open the low-side manifold valve and then closing it.
What type of refrigerant must leave the cylinder as a liquid to prevent the separation of the different components in refrigerant?
Zeotropic mixtures
For air conditioners, a rise in the return air wet bulb temperature causes
a decrease in the temperature difference across the evaporator coil
In general, a system that is overcharged will have...
a high subcooling and a low superheat
A fixed restriction system operating with a refrigerant undercharge will have
a high system superheat
A fixed restriction system operating with a refrigerant overcharge will have...
a low system superheat
An air conditioner with a thermostatic expansion valve is operating with a condenser saturation temperature of 95 degrees Fahrenheit and a liquid line temperature of 92 degrees Fahrenheit. The factory specified subcooling for the current operating condition is 10 degrees Fahrenheit. The technician should...
add charge because the system is undercharged
Most vapor charging is done with the compressor operating while charging is taking place; however, liquid charging...
can be done either with the system off or operating.
As the outdoor ambient temperature increases with fixed metering, the required superheat:
decreases
As the indoor wet-bulb temperature increases on fixed metering systems, the required superheat...
increases
A dirty air filter would likely cause which of the following symptoms?
low suction pressure
An air conditioner with a fixed restriction metering device is operating with an evaporator saturation temperature of 40 degrees Fahrenheit and a suction line temperature of 42 degrees Fahrenheit. The factory specified superheat for the current operating condition is 12 degrees Fahrenheit. After checking the airflow and determining that it is within specifications, the technician should...
recover charge because the system is overcharged
An air conditioner with a thermostatic expansion valve is operating with a condenser saturation temperature of 110 degrees Fahrenheit and a liquid line temperature of 85 degrees Fahrenheit. The factory specified subcooling for the current operating condition is 10 degrees Fahrenheit. After verifying the condenser coil and airflow are good, the technician should...
recover charge because the system is overcharged
An air conditioner is operating with low system pressures, an evaporator saturation temperature of 20 degrees Fahrenheit, and a suction line temperature of 24 degrees Fahrenheit. The suction line is frosting. The most likely cause of these symptoms is...
reduced airflow across the evaporator
Two variables that have a great impact on the system performance of air conditioning systems are:
return-air wet-bulb temperature and the airflow across the evaporator
The most reliable source of information on how to charge any particular piece of equipment is...
the equipment manufacturer
Before checking a system's operating superheat, the technician should first check...
the evaporator airflow
Why must zeotropic refrigerant leave the cylinder as a liquid?
to avoid fractionation
Which of the following types of charge is usually employed when a partial charge is required?
vapor
