A high efficiency purge unit on an R-123 chiller has a small chamber with a drain fitted to it. What routine service does that chamber need?
- AIt has to be topped up with fresh oil, because the purge compressor draws its lubricant from it
Purge compressors carry their own oil charge, and no purge is designed to be lubricated from a water separator.
- It has to be drained of the water the purge has condensed out of the air it removes
- CIt has to be filled with dry nitrogen, because that is what carries the non-condensable gas out
Nothing is added to a purge unit to carry gas out. The purge compressor moves the gas, and the separator only collects what condenses.
- DIt has to be pumped down with the recovery unit, because it holds the machine's spare charge
The chamber holds water, not a reserve of refrigerant, and a chiller does not store spare charge inside its purge unit.
Why B is correct
The purge chills the gas it removes so refrigerant condenses and can be returned to the machine. Water vapor that came in with the air condenses at the same time and collects in a separator. Draining it is part of routine purge maintenance, and the rate at which it fills is a direct measure of how much moist air the machine has been drinking.
What this question is testing
This tests understanding of what actually comes out of a machine that has been drawing air in, and of the maintenance that follows from it. The exam links moisture to air ingress repeatedly, because the acid damage that follows is the reason leaks on these machines are urgent.
On the job
Technicians who service chillers regularly open that drain on every visit and note how much comes out, because the volume is one of the cleanest indicators of how much air the machine is taking in. On a tight machine there is almost nothing. On a machine with a bad shaft seal it can be a cup a week, and every drop of it represents moisture that spent time in contact with the refrigerant and the oil before it was caught.
Memory technique
The purge's drain is a rain gauge for your leak.
Exam tip
Air brings water. Anything that removes air from a chiller ends up with water to get rid of.
Where to look it up
Moist air drawn into a chiller condenses in the purge unit, and the water it produces collects in a separator that has to be drained.