I have an Lennox XP19-060 HP connected to a G60UHV 135k gas furnace. It's about 28 degrees outside, so the system is running continuously, but maintaining temp fine. The XP19 is defrosting every 90 minutes on cue, but each time I go outside during defrost, there is no frost on any of the coils. I'm wasting gas during this time and the temp drops to about 70 degrees out of the vent during defrost from 90-95 which leaves a chill in the house. My question is, I thought the xp19 had demand defrost which didn't trigger unless frost was detected?