Some high efficiency purge units send their exhaust through an activated carbon canister before the gas leaves the building. What is that canister doing?
Correct Answer
B) Holding back the last traces of refrigerant so less of it leaves with the discharged air
Even after a purge has condensed most of the refrigerant back out, the air leaving still carries some vapor with it. An activated carbon bed adsorbs that remaining refrigerant so the discharge is closer to plain air. The carbon has a finite capacity and is replaced on a schedule, and on some designs the bed is regenerated back into the machine. The whole point is efficiency: less refrigerant lost per pound of air removed.
Why This Is the Correct Answer
Activated carbon adsorbs refrigerant vapor onto its surface, so passing the purge exhaust through a bed strips out the traces that survived the condensing stage. That directly improves the purge efficiency figure, which is measured as refrigerant lost per unit of non-condensable gas removed, and it reduces what the owner has to buy back each season.
Why the Other Options Are Wrong
Option A: Drying the gas so that the water vapor removed with the air does not condense in the vent line
The purge condenses moisture out into its own separator. The carbon bed is not there to dry the vent gas.
Option C: Filtering oil mist so that the exhaust does not stain the roof around the vent termination
Purge exhaust does not carry meaningful oil mist, and a carbon bed is not an oil filter.
Option D: Silencing the discharge so that the purge cycle cannot be heard from the occupied floors
Noise from a purge discharge is not what a carbon canister addresses, and silencers are not made of activated carbon.
Memory Technique
The carbon is a net at the door, catching the refrigerant trying to leave with the air.
Reference Hint
Purge efficiency is judged by refrigerant lost per unit of non-condensable gas removed; carbon adsorption reduces that loss.
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