HVAC Excellence Commercial Air Conditioning ESCO Certification Exam, Exams of Refrigeration and Air Conditioning

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HVAC Excellence Commercial Air

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Multiple compressor systems have a equalization line to; A. Maintain equal loads on all compressors B. Maintain equal oil levels on all compressors. C. Compensate for different pressures in the compressors. D. Compensate for evaporator pressure drop. - correct answer -A. Maintain equal loads on all compressors The purpose of a double suction line riser is to; A. maintain minimum refrigerant velocities under varying loads. B. compensate if one suction filter - drier becomes plugged. C. prevent low pressure trips on start up. D. compensate for evaporator pressure drop. - correct answer -A. maintain minimum refrigerant velocities under varying loads. To measure superheat, subtract the; A. low side saturation temperature from the suction line temperature. B. high side condensing temperature from the suction line temperature. C. suction line temperature from the ambient temperature. D. ambient temperature from the suction line temperature - correct answer -A. low side saturation temperature from the suction line temperature. An air conditioning system is running constantly, but not cooling enough. The suction line is very cold and the compressor is sweating. This is an indication of; A.) low refrigerant charge and needs to be leak tested and repaired. B.) restricted return air flow or a dirty evaporator

C. restricted air flow across the condenser. D.) damaged return air duct allowing unconditioned air to be drawn into the system. - correct answer - B.) restricted return air flow or a dirty evaporator Why must a cooling tower or evaporative condenser be blown down periodically? A. The condenser water approach will begin to narrow. B. Maintain PH level of the circulated water. C. To refresh cooling tower or condenser with cooler make-up water. D. To remove concentration of minerals in the water. - correct answer -D. To remove concentration of minerals in the water. A customer reports that their system had one of three fan motors replaced last week by another service company. Now the unit is not cooling properly since the outdoor temperature has risen. When you arrive and inspect the unit, you find that discharge pressure is very high. On further examination, all motors are running, but the amp draw is different on the new motor as compared to the other two motors. This is most likely the result of: A. fan motor is running backward B. the new motor is grossly over sized. C. a defective replacement motor. D., the fan blade was not changed to match the new motor - correct answer -B. the new motor is grossly over sized. When pumping down a condensing unit to check the reciprocating compressor valves, the compressor should be able to achieve; A. 10" Hg suction with a 300 psig high side pressure. B. 30" Hg suction when discharging to the atmosphere. C. 24" Hg suction with a 100 psig high side pressure. D. 24" psig suction with a 200 psig high side pressure. - correct answer -B. 30" Hg suction when discharging to the atmosphere. Direct Digital Control (DCC) is a control process which incorporates a microprocessor, acting as a digital controller, updates a data-base of internal information through;

A. reverse action of PTC. B. the common digital feed. C. the use of Sensors. D. the use of Sim cards. - correct answer -C. the use of Sensors. If a compressor has a severe burnout, what accessory should be added to clean the system? A. A liquid line drier. B. An accumulator. C. A suction line drier. D. An acid core oil separator. - correct answer -C. A suction line drier. The screw-type compressor operates at a high volumetric efficiency because; A. there is no re-expansion of refrigerant in the clearance space. B. they are capable of very low speed operation. C. capacity can be controlled down to 90%. D. they are used only on small capacity systems. - correct answer -A. there is no re-expansion of refrigerant in the clearance space. A rooftop package system is cycling on the high pressure control. What are three possible causes for this problem? A. Condenser air being re-circulated, plugged metering device, or undercharge. B. Excessively bent condenser fins, a faulty pressure switch, or undercharge. C. Dirty condenser, incorrect rotation of condenser fan, or bad compressor valves. D. Dirty condenser, bent condenser fins, or air re-circulated over the condenser. - correct answer -D. Dirty condenser, bent condenser fins, or air re-circulated over the condenser. An true azeotropic refrigerant blend is one which; A must be charged into the system as a liquid. B. displays the same characteristics as a single refrigerant. C. has a high temperature glide.

D. may be vented to the atmosphere if it is an HCFC. - correct answer -B. displays the same characteristics as a single refrigerant. Commercial water cooled condenser systems must incorporate a water circuit that sub-cools refrigerant by; A. water flow in the same direction as the refrigerant circuit. B. counter flowing the water (opposite of the refrigerant circuit). C. backflow with multiple check valves slowing water flow for better heat transfer. D. making the water enter the condenser where liquefaction begins. - correct answer -B. counter flowing the water (opposite of the refrigerant circuit) 14.) As refrigerant vapor density decreases, its velocity requirements; A. increase. B. decrease. C. remain the same. D. reduces by the square root of the pressure. - correct answer -A. increase 15.) An oil trap installed in the discharge line on a vertical riser is intended to: A. help move oil through the system. B. prevent oil from draining back to the compressor. C. maintain a constant pressure drop in the discharge line. D. prevent suction from excessive oil logging. - correct answer -A. help move oil through the system. When a capillary tube air conditioning system has an undercharge, what happens to the superheat and subcooling? A. The superheat increases and the subcooling increases. B. The superheat decreases and the subcooling decreases. C. The superheat decreases and the subcooling increases. D The superheat increases and the subcooling decreases. - correct answer -D The superheat increases and the subcooling decreases.

A thermostatic expansion valve with an external equalization line should be used when; A. the evaporator has a pressure drop that causes less than a 29°F change in saturation temperature B. the evaporator has a pressure drop that causes more than a 2°F change in saturation temperature. C. the system is charge with HFC refrigerant. D. the condenser has a high pressure drop. - correct answer -B. the evaporator has a pressure drop that causes more than a 2°F change in saturation What are two symptoms of a rooftop air conditioning system operating with a condenser fan-cycle control stuck in the closed position during low ambient conditions? A. Low discharge pressure and low suction pressure. B. High discharge pressure and low superheat. C. High discharge pressure and high suction pressure D. High suction pressure and low superheat. - correct answer -A Low discharge pressure and low suction pressure A system has been evacuated down to 500 microns. When the gauges are closed and the vacuum pump is turned off, the pressure starts to increase and stops at 4000 microns. This indicates the; A system has a leak and needs to be repaired. B. system has moisture in it and needs to be evacuated longer. C. vacuum pump was not run for long enough. D. oil in the compressor is saturated with air bubbles. - correct answer -B. system has moisture in it and needs to be evacuated longer. A technician has found an air conditioning system with a large leak in the liquid line. After the line is repaired, the system is evacuated and recharged. When the system is started, the compressor is noisy and running hot. The most probable cause of the noise is; A. refrigerant overcharge.

B. air in the system. C low oil in the system. D. refrigerant undercharge. - correct answer -C low oil in the system An air conditioning system that is oversized; A. can cause long compressor run time. B. will increase compressor life span. C.will increase de-humidification. D. will cause insufficient de-humidification - correct answer -D. will cause insufficient de-humidification. While troubleshooting a vapor compression system, the technician finds low operating pressures and a low system amperage draw. This could be an indication of; A.low airflow across the evaporator. B. high ambient temperature. C. a dirty condenser. D. air in the system. - correct answer -A.low airflow across the evaporator. An air conditioning contractor can set a package unit on a roof-top; for a water tight connection a ___ is used A. roof jack B. roof curb C. flat section of the roof D. silicon treated 4 X 6 timbers - correct answer -B. roof curb In a multiple compressor application, the suction lines enter a common header at the___ of the header. A top B. bottom C. sides

D.) end - correct answer -A top A 5 psig pressure drop in a suction line due to very long run will cause; A. an increase in system capacity. B a decrease in system capacity. C. high suction pressure. D. high suction temperature. - correct answer -B a decrease in system capacity. To prevent refrigerant from migrating to the compressor crankcase during the off cycle, a ____ can be installed. A suction accumulator B. crankcase heater C. time delay relay D. inlet pressure regulating valve can - correct answer -B. crankcase heater What are two variables that most be set for an economizer to function properly? A. outdoor dry bulb and wet bulb temperatures. B. indoor dry bulb and wet bulb temperatures. C. indoor dry bulb and outdoor wet bulb temperatures. D. indoor and outdoor wet bulb temperatures - correct answer -A. outdoor dry bulb and wet bulb temperatures. What is the purpose of an automatic pump-down system? A. It prevents the system from starting without a load. B.It prevents migration during the off cycle. C. It decreases the systems power consumption. D. It prevents frost build-up on the evaporator - correct answer -B.It prevents migration during the off cycle.

When charging a system using the superheat method; A. removing refrigerant from the system will decrease superheat. B removing refrigerant from the system will increase superheat. C. adding refrigerant to the system will increase superheat. D. adding refrigerant to the system will decrease head pressure. - correct answer -B removing refrigerant from the system will increase superheat. To measure subcooling, subtract; A. ambient temperature from the high side condensing temperature. B high side condensing temperature from the liquid line temperature. C. liquid line temperature from the high side condensing temperature D. the ambient temperature from the liquid line temperature. - correct answer -C. liquid line temperature from the high side condensing temperature What are two symptoms of an overcharged air conditioning system using a capillary tube metering device? A. An increase in discharge pressure and a decrease in suction pressure. B. An increase in discharge pressure and a increase in suction pressure. C. A decrease in discharge pressure and a decrease in suction pressure.. D. A decrease in discharge pressure and an increase in suction pressure. - correct answer -B. An increase in discharge pressure and a increase in suction pressure. The compressor design LEAST likely to be damaged by small amounts of liquid refrigerant slugging is the; A scroll. B. screw. C. rotary. D. reciprocating. - correct answer -A scroll.

A technician finds a 50 ton, multi-zone, two-stage roof top A/C unit, which has a seized-up first stage compressor. The second stage compressor is found to be over filled with oil. A possible cause of this failure is; A. a faulty crankcase heater. B. a plugged equalization line or oil level regulator. C. low voltage to the first stage motor. D. a faulty first stage cooling relay. - correct answer -A. a faulty crankcase heater. 34.) A conventional tube-in-tube water cooled condenser has the refrigerant and the water flowing; A in opposite directions. B. in the same direction. C. from top to bottom. D. from bottom to top. - correct answer -A in opposite directions. While troubleshooting an air conditioning system, the technician finds the evaporator to have low suction pressure, low suction gas superheat, and warm conditioned space temperature. These symptoms could be caused by; A. system overcharge. B. undersized metering device. C. low system airflow. D. a dirty condenser. - correct answer -C. low system airflow. A TEV sensor bulb that becomes detached from the suction line will cause these symptoms; A.high suction pressure and low discharge pressure. B. high suction pressure and high discharge pressure C. low suction pressure and low discharge pressure. D. low suction pressure and high discharge pressure. - correct answer -A.high suction pressure and low discharge pressure. 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; A. compressor is oversized. B.no discharge oil traps. C. bad valves from the factory. D. operating at too low ambient temperature. - correct answer -D. operating at too low ambient temperature. which controls are used on an automatic pump-down system? A. A high pressure switch cycles the liquid line solenoid and thermostat controls the contactor. B. A low pressure switch cycles the condenser fans and a thermostat controls the compressor. C. A thermostat cycles the condenser fans and a reverse acting pressure switch controls the compressor. D. A thermostat cycles the liquid line solenoid and a low pressure switch controls the compressor. - correct answer -D. A thermostat cycles the liquid line solenoid and a low pressure switch controls the compressor. Condenser fan-cycling controls have the same action as a low-pressure control, except it: A. is used on three-phase equipment only. B. operates at a much higher pressure only. C. is used to control the high pressure. D. is used with variable-speed fan motors only. - correct answer -C. is used to control the high pressure. A sling psychrometer is used to measure the wet and dry bulb temperatures. The difference between the two readings is; A. dew point temperature. B. grains of moisture. C. wet bulb depression. D.relative humidity. - correct answer -C. wet bulb depression. Some compressors are fitted with an unloading device to;

A. A prevent undesirably high evaporator pressure. B. defrost the evaporator coil. C. prevent undesirably high oil pressure. D. provide variable capacity. - correct answer -D. provide variable capacity. Compressor net oil pressure is determined by; A. oil pump discharge pressure plus suction pressure. B. absolute suction pressure divided by absolute discharge pressure. C. oil pump discharge pressure minus suction pressure. D. absolute suction pressure minus oil pressure. - correct answer -C. oil pump discharge pressure minus suction 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: A. 10: B. 8: C. 7: D. 5:1 - correct answer -D. 5: )Which type of metering device can be used to meter refrigerant and control system pump down without a liquid line solenoid valve? A. Thermostatic Expansion valve with gas charged bulb. B. Low side float used with DX evaporator. C. Balance & dual port expansion valve. D. Electronic step-motor expansion valve. - correct answer -D. Electronic step-motor expansion valve. The capacity of a cooling tower depends on the: A. fan horsepower. B. amount of heat the leaving air is capable of absorbing. C. entering air wet bulb temperature.

D. entering air dry bulb temperature. - correct answer -C. entering air wet bulb temperature When the wet and dry bulb temperature are the same the relative humidity would be: A. 100%. B. 50%. C. at the lowest level. D. lower than the dew point. - correct answer -A. 100%. Refrigerant in the suction line should be slightly superheated in order to; A. insure liquid refrigerant does not enter the compressor. B. prevent vapor lock from occurring before entering the compressor. C. prevent excessive sweating, thus eliminating expensive insulation. D. eliminate the external equalizer port. - correct answer -A. insure liquid refrigerant does not enter the compressor. On split system installations, the suction line should be pitched towards the compressor at least' A. four inches per ten feet. B. three inches per ten feet. C. two inches per ten feet. D. one inch per ten feet. - correct answer -D. one inch per ten feet. The most reliable and safest method of field charging a blended refrigerant into a system is to charge; A. a TEV system until the sight glass is clear of bubbles. B. a Cap Tube system until the sight glass is clear of bubbles. C. by weighing in the correct amount of refrigerant. D. with head pressure plus 30 method until in the acceptable range. - correct answer -C. by weighing in the correct amount of refrigerant. Approximately how much airflow is required across the evaporator per ton of cooling capacity?

A. 250-350 FPM per ton. B. 350-450 CFM per ton. C. 450-650 CFM per Horsepower. D. 650-1000 FPM per Horsepower. - correct answer -B. 350-450 CFM per ton. The amount of heat absorbed in the evaporator is equal to the heat; A. given off by the condenser minus the heat of compression. B. in the conditioned space. C. absorbed during the compression stroke in the compressor. D. given off by the condenser only. - correct answer -A. given off by the condenser minus the heat of compression. If a TEV sensing bulb has lost all of its charge, what effect would this have on the air conditioning system? It would cause the; A. high side pressure to increase to an unsafe limit. B. system to run at a very high suction pressure. C. system to run at a very low suction pressure. D. Oil pressure will decrease to a point below the suction pressure. - correct answer -C. system to run at a very low suction pressure. A decrease in water flow, when using a water cooled condenser; A. decreases the power consumption of the compressor. B. increases the fouling factor of the water. C. decreases the operating pressures. D. increases the power consumption of the compressor. - correct answer -D. increases the power consumption of the compressor. High compressor operating temperatures can be caused by: A.high volumetric efficiency. B. low discharge pressures.

C. low compression ratio. D. high compression ratios. - correct answer -D. high compression ratios. What is the purpose of a distributor? it evenly feeds refrigerant to; A. the compressor from the evaporator. B. the evaporator. C. the condenser. D. a solenoid valve. - correct answer -B. the evaporator. Upon investigation of a "no cooling" complaint, the technician finds that the blower motor of the air handler has open windings. One week ago, this same unit was found to have a broken belt caused by a worn drive pulley. Both the belt and pulley were replaced at that time.Which of the following should be done when the technician replaces the motor? A. Check for proper amp draw. B. Adjust the drive pulley to decrease amp draw. C. Use a larger horsepower motor. D. Use a smaller squirrel cage blower. - correct answer -A. Check for proper amp draw. Over-night, with lower than normal ambient temperatures, an air conditioning unit has the suction line iced up to the compressor. What would be the most probable cause? A. A dirty evaporator coil. B. A plugged air filter. C. A bad indoor blower relay. D. A low refrigerant charge. - correct answer -D. A low refrigerant charge. Depending on the application, suction lines must be ________ to assure proper oil return. A. raised B. slightly oversized. C. heavily insulated

D. trapped - correct answer -D. trapped When sizing a cooling tower, it is important to know that one pound of evaporating water can absorb. A. 970 BTU B. 144 BTU C. 8.413 BTU D. 3,413 BTU - correct answer -A. 970 BTU Polyol Ester based lubricants; A. have better lubricity and miscibility characteristics than Alkylbenzene oils. B. are used primarily with refrigerant (R-718). C. require less evacuation time than mineral oils. D. absorb atmospheric moisture more rapidly than mineral oil. - correct answer -D. absorb atmospheric moisture more rapidly than mineral oil On what type compressor does the clearance space becomes more problematic with capacity? A. Scroll. B. Reciprocating. C. Rotary. D. Screw. - correct answer -B. Reciprocating. Which of the following will cause a major change in compressor capacity when retrofitting to another type of refrigerant? A. Suction pressure. B. Discharge pressure. C. Refrigerant liquid density D. Refrigerant vapor density. - correct answer -B. Discharge pressure. A disadvantage to the reciprocating compressor over other designs is;

A. higher operating temperature, B. some refrigerant will always remain in the clearance space. C. lower operating temperature. D. the ability to pump against very high head pressures. - correct answer -B. some refrigerant will always remain in the clearance space. The flow switches of a chillers control system; A. are located in the chillers water supply only. B. control chiller operation directly. C. allow refrigeration system operation only when the water circulating pumps are energized. D. increase the possibility of tubes freezing because they restrict water flow. - correct answer -B. allow refrigeration system operation only when the Which valve will maintain a constant head pressure on a water-cooled condenser? A. A regulating flow valve. B. A ball & float valve. C. TEV water controlled valve. D. DA reverse check valve. - correct answer -A. A regulating flow valve 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 809 F, what would be the temperature of the water leaving the condenser? A. 80° F. B. 95° F. C. 100° F. D. 110° F. - correct answer -C. 100° F When refrigerant line vibration eliminators are installed on a system which uses a reciprocating compressor, the eliminators should be installed;

A. perpendicular to the compressor crankshaft. B. Parallel to the compressor crankshaft. C. vertical and in the suction line only. D. vertical and in the discharge line only. - correct answer -B. Parallel to the compressor crankshaft. In low-ambient temperature conditions, there must be a method to maintain a workable head pressure. This may be accomplished by: A. an EPR valve. B. indoor dampers. C. a liquid receiver. D. fan cycling. - correct answer -D. fan cycling When testing the efficiency of an air cooled condenser, the refrigerant condensing temperature should be approximately higher than the entering air temperature. A. 5° F to 20° F B. 15°F to 30° F C. 30° F to40°F D. 40° F to 50°F - correct answer -B. 15°F to 30° F When testing the efficiency of a water cooled condenser, the refrigerant condensing temperature should be approximately_________ higher than the leaving water temperature. A. 10°F B. 20° F C. 30°F D. 40°F - correct answer -A. 10°F The total amount of heat contained in one pound of substance is called; substance calculated from an accepted temperature. A. superheat. B. enthalpy.

C. entropy. D. latent heat. - correct answer -B. enthalpy If non-condensables are trapped in a condenser, what symptoms will be present? A. High discharge pressure, low amperage, and a decrease of efficiency. B. Low discharge pressure, high amperage, and excessive heat build-up. C. A decrease in efficiency, decreased heat build-up. and high amperage. D. Increased heat build-up. high amperage, and high discharge pressure. - correct answer -D. Increased heat build-up. high amperage, and high discharge pressure. When selecting a liquid receiver, it should be sized; A. 100% of the total liquid volume inside the system. B. 20% larger than the total liquid volume inside the system. C. 15% smaller than the total liquid volume inside the system. D. 50% of the total liquid volume in the system. - correct answer -A. 100% of the total liquid volume inside the system. When an air conditioning system is designed, compressor capacity is selected to handle: A. the peak load of the structure. B. 30% of the peak load of the structure. C. 75% of the peak load of the structure. D. double the peak load of the structure. - correct answer -A. the peak load of the structure. Many multi-cylinder reciprocating compressors have a capacity control device cailed; A. suction valve lift un-loader. B. discharge valve lift up-loader. C. a CPR valve. D. a hot gas purge bypass valve. - correct answer -A. suction valve lift un-loader.

When thermostatic expansion valves are used on system with multiple evaporators, a have ________to be incorporated into the system. A. pump down scienoid B. suction accumulator C. receiver D. oil separator - correct answer -C. receiver What are the two water systems incorporated into a low pressure chiller system? A. Make up water & Condenser water B. Chill water & Condenser water C. Make up water & Chill water D. Compressor water & Waste water - correct answer -B. Chill water & Condenser water What device is used to modulate the flow of vapor leaving the evaporator by limiting the pressure in the evaporator, and keeping it from dropping below the set point? A. TEV B. EPR Valve C. Low ambient control valve D. Automatic expansion valve - correct answer -B. EPR Valve 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. B. that the system has a low charge and must be leak tested. C. that the wrong refrigerant in the system. D. the distributor tubes are restricted. - correct answer -B. that the system has a low charge and must be leak tested. Which two pressures control the operation of a water regulating valve? The;

A. outlet water pressure and the high side pressure. B. inlet water pressure and the high side pressure. C. high side pressure and crankcase pressure. D. high side pressure and the spring pressure. - correct answer -D. high side pressure and the spring pressure. The critical charged bulb on a TEV will; A. need an external equalizer port. B. limit the maximum operating pressure. C. operate with any refrigerant that has a critical point. D. incorporate easily to a capillary tube system. - correct answer -B. limit the maximum operating pressure. In a direct expansion (DX) evaporator system, refrigerant enters the evaporator as; A. liquid only. B. vapor only. C. liquid with some "flash-gas" D. subcooled liquid only. - correct answer -C. liquid with some "flash-gas" When setting a high pressure cut-out on a R-410A system which has an air cooled condenser, the setting should be approximately: A. 300 - 320 psig. B. 350 - 370 psig. C. 450 - 470 psig. D. 600 - 620 psig. - correct answer -D. 600 - 620 psig. When is the installation of a "P" trap mandatory in a drain line? When the evaporator; A. coil is located after a heat exchanger.

B. coil is located on the positive side of the blower. C. is an "A" type coil. D. coil is located on the negative side of the blower - correct answer -D. coil is located on the negative side of the blower A pump-down system should have a; A. oil separator. B. suction accumulator. C. oil pressure safety. D. liquid receiver. - correct answer -D. liquid receiver. A temperature or pressure difference across a liquid line filter-drier usually indicates; A. normal operation. B. it's installed backward. C. a restriction D. a very high volumetric flow rate - correct answer -C. a restriction A liquid receiver is used to; A. prevent liquid refrigerant from reaching the compressor. B. separate oil from the liquid refrigerant. C. store liquid refrigerant. D. separate refrigerant vapor from the liquid. - correct answer -C. store liquid refrigerant. An accumulator is used to; A. prevent liquid refrigerant from reaching the compressor, B. separate oil from the liquid refrigerant. C. store liquid refrigerant to feed the TEV. D. return liquid refrigerant to the evaporator. - correct answer -A. prevent liquid refrigerant from reaching the compressor,

Which device should be installed in order to prevent compressor short cycling under low ambient conditions by condenser flooding? A. Low ambient control valve B. Crankcase pressure regulating valve C. evaporator pressure regulator D. step motor pressure regulator - correct answer -A. Low ambient control valve High suction pressure and low discharge pressures are an indication of: A. an overcharge of refrigerant. B. a low refrigerant charge. C. high compression ratio. D. defective compressor valves - correct answer -D. defective compressor valves During the off-cycle. a capillary tube metering device type system will continue to feed the evaporator until the: A. receiver is empty. B. high and low pressures balance. C. pump-down solenoid closes. D. accumulator is empty. - correct answer -B. high and low pressures balance. Which of the following is TRUE of a solenoid in a pump down system? A. It is located after the metering device. B. It is located before the metering device C. It is located after the evaporator. D. it is used instead of a metering device. - correct answer -B. It is located before the metering device Variable-speed condenser fan motors, when used on larger condensers have; A. a damper control to change the voltage frequency to the fan motor.

B. an inverter VFD control to change the voltage frequency to control the motor speed. C. pressure controls which changes the frequency to the motor. D. outdoor thermostats which controls the voltage frequency to the motor. - correct answer -B. an inverter VFD control to change the voltage frequency to control the motor speed. A liquid-to- suction line heat exchanger is often used to; A. decrease superheat. B. increase subcooling. C. lower the head pressure. D. remove frost from the suction line. - correct answer -B. increase subcooling. The oil pressure safety switch is operated by: A. the sum of suction pressure and oil pump pressure. B. the sum of oil pump pressure and crankcase pressure. C. the difference between crankcase pressure and oil pump pressure. D. the difference between head pressure and oil pump pressure. - correct answer -C. the difference between crankcase pressure and oil pump pressure. A low pressure cut-out switch is used to; A. establish a minimum operating pressure in the evaporator. B. prevent condensing pressure from reaching dangerously high levels. C. sense oil pressure in the lower portion of the compressor. D. cycle evaporator blower, - correct answer -A. establish a minimum operating pressure in the evaporator Screw-type compressors used in high temperature applications: A. are less efficient than reciprocating compressors. B. are cheaper to manufacture than 2 stage compressors. C. are less tolerant of high compression ratios.

D. used a slide valve for capacity control. - correct answer -D. used a slide valve for capacity control. Which of the following is the opening force on a water regulating valve, being used on a water cooled condenser? A. Low side pressure. B. Crankcase pressure. C. Spring pressure. D. High side pressure - correct answer -D. High side pressure Multi split systems use; A. system reheat capability for higher efficiencies. B. heating and cooling coils back to back in one case. C. single stage cooling and 3 stage heat D. multi evaporators for zoned areas of cooling. - correct answer -D. multi evaporators for zoned areas of cooling. What is the common static pressure for commercial duct systems? A. 01 to 05 inches of water column B. 0.1 to 0.5 inches of water column C. 1.0 to 3.0 inches of water column D. 3.5 to 5.0.inches of Mercury - correct answer -C. 1.0 to 3.0 inches of water column