I just want to double check this method. My 15 year old Lennox HP is a little low on refrigerant charge per the pressure charts in the manual. (about 40 psi low on suction and 50 psi low on the high side relative to the charts)
Lennox states when adding charge, (as opposed to complete evac. and recharge), to heat home to 74, switch HP to AC mode, turn thermostat to 68 degrees and block the condenser vents to build up some high side pressure. Then introduce refrigerant until parameters are correct per their charts.
I have no reason to doubt this. I just wanted to make sure this method is applicable in winter ambient temps. (ie 40-50 outside ambient)