On Saturday, September 27, 2014 7:48:24 AM UTC-4, Stormin Mormon wrote:

Precharged (in HVAC terminology) means that the outdoor

unit comes with a couple pounds of refrigerant already

in the unit. The installer solders or brazes the tubing

onto the unit (tubing that goes to the indoor coil) and

then opens the service valves.



What Tim suggests is that the installer vacuum pump the

air out of the system, and put in "just the right"

amount of refrigerant. Using temperature and pressure to

know when it's got enough.


Yeah.
There seem to be 3 ways to charge. In descending order of correctness, 1) use temperature and pressure to get it exactly right; 2) weigh the charge and put in the manufacturer's recommendation; 3) add charge until it feels about the same temperature as a cold beer can. You'd be surprised how often 3) is used.