Tonage Rating of Air Conditioner Unit Re: Tonage Rating of Air Conditioner Unit Although I teach HVAC classes, I've never had anyone say they could tell the size of the HVAC unit accurately by the size of the freon line??? Expand on this please. I am curious about your statement, do you use O.D. Caliphers to determine the sze of the line? Anyhoo, I thought you guys up in Canada did'nt require A/C or do you require it because of all the hot air blowing out of the states? Scott, I don't believe that the amperage helps at all as the amps draw varries very much due to the efficiency of the unit. Older units inherently have higher amperage draws than newer ones. "To realize our true destiny, we must be guided not by a myth from our past, but by a vision of our future." NACHI Education & Training Consultant Commercial property Inspection Tampa, Orlando, Sarasota, Jacksonville, Ft Launderdale, Miami, Florida.NACHI cell 484-429-5466Home inspection Clearwater, St Petersburg, Tampa.