HVAC Excellence Test Commercial AC, Exams of Refrigeration and Air Conditioning

Download HVAC Excellence Test Commercial AC and more Exams Refrigeration and Air Conditioning in PDF only on Docsity! HVAC Excellence Test Commercial AC 2024-2025. Questions & Correct Answers. Graded A+ 10 lbs. of refrigerant passing through a water-cooled condenser will give up 20 Btu's of heat per lb. If 10 lbs. of water passes through with an entering temperature of 80° F, what would be the temperature of the water leaving the condenser? - ANS100F A 5 psig pressure drop in a suction line will cause; - ANSdecreased system capacity. A compressor is operating with a discharge pressure of 185.3 psig and a suction pressure of 25.3 psig. The compression ratio (pumping ratio) is: - ANS5:1 A conventional tube-in-tube water cooled condenser has the refrigerant and the water flowing: - ANSin opposite directions. A customer calls on the first hot day in the spring and complains of no cooling. On inspection, you find that the sight glass indicates a full charge, the liquid line is hot, and the unit is cycling on the high pressure safety switch. This could be caused by: - ANSan inoperative condenser fan. A customer calls with an insufficient cooling complaint on a 95°F day. This R-22 system is operating at 45 psig on the low side and 160 psig on the high side. The evaporator Is partially frosted, and all of the distributor circuits have frost on them. This is an indication; A. that the system has an over-charge refrigerant must be recovered. - ANSthat the system has a low charge and must be leak tested. A customer reports that their 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 for refrigerant. On further examination, you find that the liquid line is sweating where it leaves the drier. This is most likely the result of: - ANSdebris from the burned out compressor has clogged the drier. A decrease in water flow, when using a water - cooled condenser - ANSincreases the power consumption of the compressor. A disadvantage to the reciprocating compressor over other designs is - ANSsome refrigerant will always remain in the clearance space. A liquid receiver is used to: - ANSstore liquid refrigerant. A liquid- to- suction line heat exchanger is often used to; - ANSincrease subcooling. A low pressure cut-out switch is used to: - ANSestablish a minimum operating pressure in the evaporator. A low-side float metering device is used: - ANSon a flooded evaporator. A newly installed 100 ton open drive compressor is found with valve damage. The condenser is roof top remote and the compressor is in the basement, 60 feet below. operational readings were recorded for one week prior to the breakdown with no abnormalities. The cause of the valve damage could have been: - ANSno discharge oil traps. A pilor- ANSincrease Compressor net oil pressure is determined by - ANSoil pump discharge pressure minus suction pressure. Condenser fan-cycling controls have the same action as a low- pressure control except it: - ANSIs used to control the high pressure also. Depending on the application, suction lines may be ______ to assure proper oil return. - ANStrapped During the off-cycle, a capillary tube metering device type system will continue to feed the evaporator until the; - ANShigh and low pressures balance Frost on the suction line indicates; - ANSa low refrigerant charge. Got Gas Bypass refers to a method of - ANSpreventing low suction pressure. High compressor operating temperatures can be caused by - ANShigh compression ratios. High suction pressure and low discharge pressures are an indication of: - ANSdefective compressor valves. If a compressor has a severe burnout, what accessory should be added to rid the system of acid? - ANSAn acid core suction line drier. If a TEV sensing bulb has lost all of its charge, what effect would this have on the air conditioning system? - ANSIt would cause low side pressure to increase. If non- condensables are trapped in a condenser what symptoms will be present? - ANSIncreased heat build-up, High amps, and high discharge pressure. In a direct expansion (DX) evaporator system, refrigerant enters the evaporator as; - ANSliquid with some "flash-gas" In a multiple compressor application, the liquid lines enter a common header at the of the header. - ANSbottom In a multiple compressor application, the suction lines enter a common header at the of the header. - ANStop In low-ambient temperature conditions, there must be a method to maintain a workable head pressure. This may be accomplished by - ANSfan cycling. In order to prevent compressor short cycling under low load conditions, a installed - ANSevaporator pressure regulator Many multi-cylinder reciprocating compressors have capacity control device called - ANSan unloader. Multiple compressor systems have a balance line to; - ANSmaintain equal loads on all compressors during operation. Multiple evaporators are used to provide; - ANSzoned areas of cooling. On split system installations, the suction line should be pitched towards the compressor at least - ANSOne inch per ten feet. Polvolester oils - ANShave more atmospheric moisture than mineral oil. Refrigerant in the suction light should be slightly superheated in order to - ANSinsure liquid refrigerant does not enter the compressor. Screw-type compressors used in high temperature applications; - ANSused a slide valve for capacity control. Some compressors are fitted with an unloading device to - ANSprovide variable capacity. the amount of heat absorbed in the evaporator is equal to the heat - ANSgiven off by the condenser minus the heat of compression. The capacity of a cooling tower depends on the - ANSEntering air wet bulb temperature. The clearance space in a reciprocating compressor - ANShas an effect on compressor capacity. The compressor design LEAST likely to be damaged by small amounts of liquid refrigerant slugging is the; - ANSscroll. The flow switches of a chiller's control system - ANSAllow refrigeration system operation only when the water circulating pumps are energized The most reliable and safest method of field charging a system is to charge - ANSby weight according to the manufacturer's specifications The oil pressure safety switch is operated by; - ANSthe difference between crankcase pressure and oil pump pressure. The purpose of a double suction line is to; - ANSmaintain minimum refrigerant velocities under varying loads. The screw-type compressor operates at a high volumetric efficiency because; - ANSthere is no re-expansion of refrigerant in the clearance space. The total amount of heat contained in one pound of a substance calculated from an accepted temp base is called - ANSEnthalpy To control capacity, the hot gas from the bypass valve is piped into the; - ANSevaporator outlet To measure subcooling subtract; - ANSliquid line temperature from the high side condensing temperature. To measure superheat, subtract the; - ANSlow side saturation temperature from the suction line temperature To prevent refrigerant from migrating to the compressor crankcase during the off cycle, a can be installed. - leaving water temperature. - ANS10F When testing the efficiency of an air cooled condenser, the refrigerant condensing temp should be approximately _______ higher than the entering air temperature. - ANS30-40F When thermostatic expansion valves are used on a system with multiple evaporators, a ______ will have to be incorporated into the system. - ANSpump down solenoid. Which controls are used on an automatic pump-down system? - ANSA thermostat cycles the liquid line solenoid and a low pressure switch controls the compressor. Which of the following is the opening force on a water regulating valve, being used on a water cooled condenser? - ANSThe high side pressure Which of the following is TRUE of a solenoid in a pump down system? - ANSIt is located before the metering device. Which of the following will cause a major change in compressor capacity when retrofitting to another type of refrigerant? - ANSDischarge pressure Which two pressures control the operation of a water regulating valve? - ANShigh side pressure and the spring pressure. While troubleshooting a vapor compression system, the technician finds low operating pressures and a low system amperage draw. This could be an indication of; - ANSlow airflow across the evaporator. While troubleshooting an air conditioning system, the technician finds the evaporator to have low suction pressure, low suction gas superheat, and high space air temperature. These symptoms could be caused by; - ANSlow system airflow.