Some flashing at the metering device is normal: it cools the remaining liquid to evaporator temperature. Flash gas in the liquid line, before the metering device, is a problem. It comes from low charge, too little subcooling, a restricted filter-drier, long vertical lifts or undersized lines, and it shows as bubbles in a sight glass and a starved, poorly performing evaporator.
Sight glass is full of bubbles and the drier's cold on the outlet, that's flash gas from a plugged drier.
Also heard as
- flashing
- flash
Related terms
Subcooling
How many degrees liquid refrigerant is below its condensing temperature at the same pressure.
Filter-drier
A canister of desiccant in the refrigerant line that traps moisture, acid and debris.
Starved
Describes an evaporator not getting enough refrigerant, so part of the coil runs warm and superheat is high.
Metering device
The restriction that drops refrigerant from high side to low side pressure and controls how much enters the evaporator.