Air conditioning Certification practice test fully solved & updated

What is the movement of heat through space called? - answer-Radiation A refrigerant release heat when - answer-It condenses Why is it desirable for refrigerant in the suction line to be slightly superheated? - answer-To insure liquid refrigerant does not enter the compressor A 30 pound cylinder of reclaimed R-22 refrigerant has been stored over night at 70 degrees F. What should be the approximate pressure in the cylinder? - answer-121 psig 14.7 psia( pouds per square inch absolute) is - answer-Approximately 0 PSIG What is the main fuction of an air condition condenser? - answer-To remove heat from the refrigerant Refrigerant R-134a vapor enters the condenser at 124 psig, 100 degrees F. It leaves the condenser at 80 degreesF. What will be the approximate pressure? - answer-124 psig (the pressure should not change entering or leaving the condenser) Which of the following CANNOT be used as a low ambient temperature control? - answer-Crankcase regulating valve When testing the efficiency of a (10 seer are lower) air cooled condenser, the refrigerant condensing temperature should be no more than_______ higher than the entering air temperature - answer-Approximately 30 degrees F When testing the efficiency of a water cooled condenser, the refrigerant condensing temperature should be no more _____ higher than the leaving water temperature. - answer-10 degrees F What does a temperature differential across a filter-drier indicate? - answer-Restricted filter-drier Which of the following symptoms would be indicative of an oil logged evaporator? - answer-Reduce heat transfer through the walls of the coil When using an electronic leak detecto, the sensor probe - answer-should be moved at approximately 1 inch per second Before a vapor / compression system is opened for service - answer-the refrigerant must be recovered using approved equipment What is the minimum vertical drop from the outlet of the condensate drain pan to the inlet of the P trap when the evaporator is ahead of the blower? - answer-3 inches The temperature rise method of determining air volume CFM is mostly used with a/an; - answer-electric resistive heat air handler What is a sling psychrometer used to measure - answer-wet and dry bulb temperature A compressor is operating with a discharge pressure of 235.3 psig and a suction pressure of 35.3 psig. What is the compression ratio (pumping ratio)? - answer-5:1 (235.3+14.7=250) and (35.3+14.7=50) so 250/5=5 What method does hot gas bypass refer to? - answer-Capacity control IF a TEV sensing bulb has lost of its charge, What effect would this have on the air conditioning system - answer-It would cause the low side pressure to decrease An increase in water flow, when using a water cooled condenser, would - answer-decrease the operating discharge pressure The clearance space in reciprocating compressor - answer-has an effect on compressor capacity What is used to control the flow of water on a water-cooled condenser? - answer-A water regulating valve How should metallic vibration eliminators be installed on a system which uses a reciprocating compressor? - answer-parallel to the compressor crankshaft The total amount of heat contained in one pound of a substance calculated from an accepted temperature base is called - answer-enthalpy If non-condensables are trapped in a condenser, what symptoms will be present? - answer-Increased heat build-up, high amperage and high discharge pressure. Many multi-cylinder reciprocating compressor have a capacity control device called; - answer-un-loaders A pilot-operated pressure regulator uses_________ pressure to operate the valve. - answer-suction gas A low-side float metering device is used________. - answer-on a flooded evaporator In a direct expansion (DX) evaporator system, refrigerant leaves the evaporator as ______. - answer-superheated vapor When setting a high pressure cut-out on a R-22 system which has an air cooled condenser, the setting should be approximately _______. - answer-395 psig. The cutout must be set approximately 50% above the operating pressure When is the installation of a "P" trap mandatory in a drain line? - answer-When the evaporator coil is located on the negative side of the blower. A pump-down system should have a (an); - answer-liquid receiver. What is a liquid receiver used for? - answer-To store liquid refrigerant The oil pressure safety switch is operated by _________. - answer-the difference between crankcase pressure and oil pump pressure Which of the following is the opening force on a water regulating valve being used on a water cooled condenser? - answer-The high side pressure What is the "G" terminal used for on a heating and cooling thermostat? - answer-The blower relay. When should a thermostatic expansion valve with an external equalization line be used? - answer-When the evaporator has a pressure drop that causes more than 2°F saturation temperature change An thermal expansion valve that is stuck wide open will cause ___________. - answer-a flooded evaporator A properly functioning condenser should always have ______________ leaving the condenser; - answer-sub-cooled, liquid Tube within a tube, shell and coil, and shell and tube are all types of: - answer-water cooled condensers. What is one of the main reasons that reciprocating compressors are not 100% efficient? - answer-clearance volume Where is an open drive compressor most likely to develop a refrigerant leak? - answer-shaft seal The automatic expansion valve (AEV) maintains a constant ______ in the evaporator. - answer-pressure Short cycling during pump down can be caused by: - answer-a leaking compressor suction valve What is a crankcase heater used to prevent? - answer-Refrigerant migration to the compressor crankcase during the off-cycle. The type of compressor that allows access to the internal components is the _______. - answer-reciprocating semi-hermetic What do water cooling towers require? - answer-Periodic de-scaling When a compressor service valve is in the cracked position, which port is closed? - answer-None are closed . When the service valve is in the cracked position all ports are open Why must an oil separator be kept warm? - answer-To prevent refrigerant from condensing in the separator during the off cycle. Which part of the system stores refrigerant until it is needed in the evaporator: - answer-the receiver Which part of the system prevents liquid from entering the compressor: - answer-the accumulator A split-system air conditioning unit has: - answer-the compressor and condenser connected by a refrigeration line set to the metering device and evaporator In a sealed system, as the pressure increases: - answer-the temperature increases A room thermostat should be mounted - answer-near a return-air grill What is the purpose for insulating a suction line: - answer-to prevent condensation from forming A typical evaporator superheat reading at the evaporator outlet for a central air-conditioning system on a 95°F day would be ____°F. - answer-is: 10-12 As a rule of thumb, the air leaving the evaporator will be about ____ than the air entering the evaporator. - answer-The correct answer is: 17-20° cooler With a rise in outdoor temperature, the head pressure will rise - answer-True refrigerant overcharge - answer-- high operating pressures, refrigerant undercharge - answer-- low operating pressures blocked/dirty filter - answer-- low operating pressures, non-condensable gas in system - answer-- high operating pressures, defective condenser fan motor - answer-- high operating pressures, defective evaporator fan motor - answer-- low operating pressures, dirty condenser coil - answer-- high operating pressures If the metering device malfunctions and gets stuck in the closed position, the compressor could overheat. - answer-'True'. Superheat occurs in the condenser as well as the evaporator. - answer-True' If a compressor has a partially shorted winding, it could run for a while, overheat, and shut off. - answer-'True' When would it be beneficial for a technician to pump a system down before servicing? - answer-when the thermostatic expansion valve needs to be changed To accurately add refrigerant to a system, a condenser ambient temperature of ____°F should be simulated. - answer-95 Why does a high efficiency condenser operate at much lower head pressures? - answer-The high efficiency condenser has a larger surface area and uses modern alloy surfaces and fins. This allows the condenser to reject heat much more rapidly. This brings temperature down and reduces the head pressure. What type of metering device do you find on a high efficiency system? - answer-High efficiency systems use a TXV rather than a fixed bore device. How do you determine EER? - answer-It is the amount of output in BTUH divided by the number of input in Watts. 36000 Btuh / 4000 W = EER of 9 How do you determine EER? - answer-It is the amount of output in BTUH divided by the number of input in Watts. 36000 Btuh / 4000 W = EER of 9 What is SEER? - answer-It is an efficiency rating system that takes includes the startup and shutdown cycles. When measuring high voltage, what are the parameters for 115V and 208V/230V? - answer-It is ± 10% of the rated voltage. For 115V, that would be 104V - 126V. For 208V/230V that would be 187V - 253V What is the approach temperature? - answer-Also known as temperature split. It is the difference in temperature between heat exchange mediums. Example would be the temp difference between the indoor coil and the return air for an AC system. What is a service valve? - answer-It is a valve that can be used to isolate the system for service. It is usually manually operated. Why should you use a short gauge hose on the high side? - answer-If you used a long hose, the amount of liquid refrigerant in the hose may be enough to affect the system charge and gauge readings. What should be the highest discharge line temperature? - answer-It should not exceed 220°F. What situations can cause high compression ratios? - answer-They can result from low suction pressures, high condensing pressures, or combination of both. If no crankcase heat is at the compressor, what may happen to the refrigerant charge? - answer-The charge may migrate to the crankcase. Reducing the CFM through the evaporator will cause the amperage draw of the compressor to - answer-decrease Where is the correct location for a sight glass in order to check the charge? - answer-At the metering device on the condenser side. If the suction pressure is low and the suction line is warm, the system has a _____ evaporato - answer-Starved What electrical test instrument is used to measure continuity in a compressor winding? - answer-Ohmmeter - answer-