When adding oil to a refrigeration system, precautions must be taken to ensure that

A．the compressor suction pressure is not too high

B．all air is purged from the pump and charging fittings

C．the high pressure cutout switch is held open to prevent accidental starting

D．the condenser is completely shutdown first

[单选题]When the refrigeration demand is small,_______.A．the expansion valve will move toward the wide open positionB．the expansion valve will move toward the closing positionC．the feeler bulb will conveys the high temperatureD．the superheat degree will rais

[单选题]When the fuel oil is burning in the combustion chamber, it _____.A．gives up large amount of heatB．gives off large amount of heatC．gives up large amount of steamD．gives off large amount of steam

[单选题]When the fuel oil is burning in the combustion chamber, it （）.A . gives up large amount of heatB . gives off large amount of heatC . gives up large amount of steamD . gives off large amount of steam

[单选题]When fuel oil has seriously contaminated a diesel engine lubricating oil, you should （）.A . filter to remove the fuel oilB . use the settler to remove the fuel oilC . remove the fuel oil by centrifugingD . drain and then renew the lube oil supply

[单选题]When centrifuging heavy fuel oil, an important factor to consider is the （）(1) flow rate(2) viscosity of the fuel oilA . (1) only is correctB . (2) only is correctC . both (1) and (2) are correctD . neither (1) or (2) are correct

[单选题]If the refrigeration compressor crankcase is sweating, the cause may be due toA．a shortage of refrigerantB．the compressor running continuouslyC．liquid refrigerant returning to the compressorD．the compressor short cycling on the high pressure cutout

[单选题]In the refrigeration system, a shortage of refrigerant is indicated byA．the compressor short cycling on high pressure cut out switchB．high suction pressureC．high head pressureD．bubbles in the sight glass

[单选题]In the absence of external forces，adding weight on one side of a floating vessel causes the vessel to ().A．heel until the angle of loll is reachedB．list until the center of buoyancy is aligned vertically with the center of gravityC．trim to the side o

[单选题]Inside the computer, the operation system(of another software module called a data communication(71))must decide which program will get control next. Each program remember, is associated(72). a particular front -end port. If a program's data have no

[单选题]If a refrigeration compressor is short cycling on high head pressure, you shouldA．purge the condenser if the waterside is dirtyB．check for proper water flow through the condenserC．increase the high pressure cutout settingD．reduce the cooling water fl