Where is a moisture-indicating sight glass normally installed?
- In the suction line after the evaporator
- In the discharge line before the condenser
- In the liquid line after the filter-drier
- In the liquid line before the receiver
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C. In the liquid line after the filter-drier
Placed downstream of the drier, the sight glass shows whether solid liquid is reaching the expansion valve and whether the drier is keeping the refrigerant dry. Bubbles there can mean low charge, a restriction upstream or too little subcooling.
Reference: System accessories; liquid line sight glass
Why must containers of polyolester (POE) oil be kept tightly sealed until the oil is used?
- POE oil evaporates quickly at room temperature
- POE oil hardens when it is exposed to light
- POE oil absorbs moisture from the air very readily
- POE oil separates into layers if it is exposed to air
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C. POE oil absorbs moisture from the air very readily
POE oil is strongly hygroscopic. Moisture it picks up is hard to remove even with a deep vacuum, and in the system it reacts with the oil to form acids. Only as much as will be used should be opened.
Reference: Refrigeration oils; POE handling
Why is a P-trap installed at the bottom of a vertical suction riser?
- It collects liquid refrigerant so that it can boil off before the riser
- It slows the vapor so that oil can drain back down to the evaporator
- It absorbs vibration from the compressor before it reaches the coil
- It collects oil so the vapor can pick it up and carry it up the riser
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D. It collects oil so the vapor can pick it up and carry it up the riser
Oil draining to the foot of the riser gathers in the small trap, where the fast-moving vapor breaks it up and sweeps it upward. Without the trap, oil spreads out along the horizontal line and is harder to lift.
Reference: Refrigerant piping; suction riser traps