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hvac excelence
| Question | Answer |
|---|---|
| 1-heat which cause a change in the temperature of a substance is called | sensible heat |
| 2-heat added to a substance without a rise in temperature;(example:liquid refrigerant to gas) this process is called? | latent heat of vaporization |
| 3-heat added to a refrigerant in a vapor state after the evaporation process is called; | super heat |
| 4-a scroll compressor move refrigerant by means of; | involutes spiral |
| 5-the movement oh heat by way of fluid (or air) is called; | convection |
| 6-the movement of heat bythrough a solid object is called; | conduction |
| 4-the standard unit for measuring the quantity of heat in a substance is; | the british thermal unit(btu) |
| 8-a refrigerant gives heat when; | it condense |
| 9-why must refrigerant in the suction line slightly warmer than the saturation temperature? | prevent liquid slugging of the compressor |
| 10-the state of the refrigerant in the suction line should be; | low pressure/low temperature vapor |
| 11-the state of the refrigerant entering the condenser is; | low pressure/low temperature vapor |
| 12-the evaporator | transfers heat from the refrigerated space to the refrigerant |
| 13-which of the following is nit a thermodynamic property of refrigerant? | flammability |
| 14-the sequential order of steps in the evaporator-compressor are; | compression,condensation,expansion,vaporization |
| 15-if a 30 pound cylinder if reclaim R-410a refrigerant has been stored overnight at 70F,the pressure in the cylinder should be approximately | 201 psig |
| 16-fan airflow pressure are usually measured in | inches of water column(WC) |
| 17-zero psia(pound per square inch absolute ) is | a pressure which can not be further reduced |
| 18-zero psig (pounds per square inch gauges) is | the same as atmospheric pressure |
| 19-the temperature at which a moisture ill start to condense from the air is called | dew point temperature |
| 20-a compound pressure gauges measure | pressure and vacuum |
| 21-a mechanical shaft seal is necessary on a | hermetic rotatory compressor |
| 22-liquid slugging is | liquid refrigerant in the compressor clearance space |
| 23-the clearance space in a reciprocating compressor | has on effect on compressor capacity |
| 24-which of the following types of air conditioning compressors is most energy efficiency? | scroll |
| 25-which of the following represent the right order for the function of a condenser? | de-superheats,condenses,sub-cools |
| 26-refrigerant R-134a vapor enters the condenser at 124 psig, 100F .it leaves as liquid from the condenser sub-cooled 20F and the pressure will be approximately | 87 psig |
| 27-there are three basic types of condensers,the air cooled, the water cooled and the ___________colled | evaporative |
| 28-10 lbs of refrigerant passing through a water cooled condenser will lose 20 btus of heat per lb. if 10 lbs of water passes through the condenser with an entering temperature of 80 F. the temperature of the water leaving the condenser is: | 100F |
| 29-the heat removed from the refrigerant by the condenser is | both sensible and latent heat |
| 30-an energy recovery ventilator is; | am air to air heat-exchanger to recovery heat |
| 31-when testing the efficiency of an air cooled condenser,the refrigerant condensing temperature should be approximately ______ higher than the entering air temperature | 30F |
| 32-when testing the efficiency of a water cooled condenser, the refrigerant condensing temperature should be aproximately______higher than the leaving water temperature | 10F |
| 33-the first function a condenser must perform is to _____the refrigerant before condensing can occur. | de-superheat |
| 34-a thermostatic expansion valve is design to maintain; | constant evaporator superheat |
| 35-the automatic expansion valve is design to maintain | constant evaporator pressure |
| 36-the thermostatic expansion valve has three operating pressures | evaporator pressure,spring pressure and sensor bulb pressure |
| 37- when a thermostatic expansion valve sensor bulb, which of the following is not true? | it must be install lower than the valve body |
| 38-in an air conditioning system that uses a thermostatic expansion valve, the temperature of the evaporator outlet usually be; | warmer than the evaporator inlet |
| 39-an automatic expansion valve is best suited | when the system load remain fairly constant |
| 40-which of the following is not true of a capillary tube metering device? | they maintain a constant evaporator temperature |
| 41-a decrease in super heat cause the thermostatic expansion valve to begin to | close |
| 42-a rise in evaporator pressure causes the automatic expansion valve to begin to | close |
| 43-a thermal-electric(solid state) expansion valve is controlled by | NTC thermistor |
| 44-in a direct expansion(DX) evaporator system, the refrigerant enters the evaporator as | a mixture liquid with some" flash gass" |
| 45-which of the following is the most important consideration in the selection of an evaporator coil? match the coil to the: | condensing unit and the latent/sensible loads |
| 46-in the evaporator | latent heat is transferred from the refrigerant space to the refrigerant |
| 47-a liquid line filter-drier should be place between the | condenser and the metering device |
| 48-the only way to minimise flash gas is by | sub-cooling the liquid refrigerant entering the metering device closer to the evaporator temperature |
| 49-a liquid receiver is use to; | store liquid refrigerant |
| 50-an accumulator is used to; | prevent liquid refrigerant to reaching the compressor |
| 51-a sight glass would be normally located | in the liquid line,before the metering device |
| 52-bubbles in the sight glass could be an indication of | a refrigerant blend with a high temperature glide |
| 53-the oil separator is installed in the | discharge line |
| 54-which of the following is true of a solenoid valve in a pump down system? | it is located before the metering device |
| 55-the purpose of an evaporator pressure regulating valve (EPR) is to ; | prevent evaporator pressures from falling bellow a set limit |
| 56-a liquid -to - suction heat exchanger is often use to; | increase liquid sub-cooling |
| 57-the oil pressure safety switch is operated by | the difference between crankcase pressure and oil pressure |
| 58-a low pressure cut-off switch is used to; | establish a minimum operating pressure in the evaporator |
| 59-a partially iced over evaporator can caused by | an undercharge |
| 60-_________can be cause for leak detection with all high pressure refrigerant. | soap bubbles |
| 61-the flow rate of a TXV used in R-410a systems as compared to R-22 system is; | aproximily 15 % less |
| 62-when using an electronic leak detector ,the sensor probe; | should be moved at approximately 1 inch every 2 seconds |
| 63-moisture in a refrigeration system will cause; | compressor failure |
| 64-in order to remove as much moisture as possible from a system; | triple evacuate the system to 500 microns with a deep vacuum pump |
| 65-what type of gauges is used to measure microns? | an electronic vacuum gauge |
| 66-water will vaporize at__________temperature in a 28 in Hg vacuum | 100F |
| 67-after a system has been opened and the compressor changed,the service technician must; | replace the filter drier , leak check , evacuate and charge |
| 68-back seating a two way service valve result in; | closed service port with normal system flow |
| 69-the R-410a compound gauge reads 124 psig and the suction line temperature at the condensing unit is 54 degrees F. what is the operating system superheat? | 12 degrees F |
| 70-when topping off an operating system containing a blended refrigerant; | introduce the refrigerant as a liquid into the low side using a throttling valve |
| 71-a partially clogged capillary tube can cause; | a starved evaporator |
| 72-the R123a high pressure gauge reads 146 psig and the liquid line temperature at the condensing unit is 95 degrees F.what is the operating system subcooling? | 15 degrees F |
| 73-an overcharge of refrigerant ill cause | increase head pressure |
| 74-a customer complains that their conditioning system is running constantly, but not cooling enough.the suction line is very cold and the compressor is sweating. the most likely cause is; | a restriction of the return air or dirty evaporator |
| 75-a drain trap should be install on a split system when the; | air handler drains is on the negative air side |
| 76-a customer complain 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 exami | debris from a burned out compressor has clogged the drier |
| 77-whats is the generally accepted range for evaporator air flow in CFMs per ton of residential air conditioning? | 350 to 450 |
| 78-the temperature rise method for determining air flow is, | CFM = BTU / (1.08*delta T) |
| 79-what is the recommended residential indoor relative humidity for summer? | 50 % |
| 80-an inefficient compressor is usually indicated by _________head pressure and ________ suction pressure | lower than normal/ higher than normal |
| 81-which of the following is not a symptom of a hermetic system that is low on refrigerant? | high head pressure |
| 82-frost on the suction line indicates; | that its temperature is below the dew point and below 32F |
| 83-an increase in head pressure cause ________ refrigerant to flow through a capillary tube. | more |
| 84-with an automatic expansion valve, an increase in evaporator load will cause the; | automatic expansion valve to close |
| 85-when a TEV or capillary tube is used as a metering device ,a low refrigerant charge will cause; | low head pressure |
| 86-what is the maximum operating pressure for an acetylene torch? | 15 psig |
| 87-when connecting copper to steel, the recommended brazing filler alloy is a: | 45 percent silver alloy |
| 88-solid contaminants, such sludge and carbon, from a server hermetic compressor motor burn out are best removed; | by flushing the system and then installing filter / drier in both the liquid and suction line |
| 89-if the cutt-off plate is removed from a blower assembly, how would this effect blower performance? | it would reduce air flow |
| 90-at a residential service call, " no cooling " complaint , the service technician finds the unit to be completely out of refrigerant. the technician decides to use a trace amount of refrigerant and _____ in order to pressurize the system | an inert gas |
| 91-a techinitian has found an air conditioning system with a leak in the liquid line. after the line is repaired,the system is evacuated and properly recharged. when the system is started, the compressor is noisy and running hot. the most probalble cause | low oil in the system |
| 92-an air conditioning system that is oversize can cause | improved dehumidification of the conditioned space |
| 93-while troubleshooting a residential split system, the service technician finds low operating pressures and low system amperage draw. this could be an indication of; | low airflow across the evaporator |
| 94-air or other non-condensable gases in a capillary tube air conditioning system will cause these symptom; | high suction pressure and high discharge pressure |
| 95-a refrigerant overcharge in a capillary tube air conditioning system will cause these symptoms; | high suction pressure and high discharge pressure |
| 96-a compressor thats has a broken reed valve ill cause these symptoms; | high suction pressure and low discharge pressure |
| 97-a low refrigerant charge in an air conditioning system will cause these symptoms; | low suction pressure and low discharge pressure |
| 98-a TEV sisnive bulb which becomes detached from the suction line will cause these symptoms; | high suction pressure and higher than normal discharge pressure |
| 99-a faulty condenser fan motor on an air conditioning system will cause these symptoms; | high suction pressure and high discharge pressure |
| 100-a dirty evaporator in an air conditioning system will cause these symptoms; | low suction pressure and low discharge pressure |
Created by:
carralero1982