17) Which device meters the amount of refrigerant entering the evaporator in window AC?

18) Which gas is used for flushing blocked capillary tube?

19) Which component is connected in series with bimetal thermo in a frost free refrigerator?

20) Which cooling medium is used to condense the refrigerant vapour in plate and tube condenser?

21) Which gas is used to flush out the coils of air cooled condenser?