Thanks for your work. I have a Trane XL15i Model 41XW5038A1000BA installed last year. We live at 3500 feet with lots of snow. Have had a severe frosting problem this winter. Cut J2 jumper (per my installer) which increases defrost cutoff temp from 47 to 70 degrees, and defrost every 3 hours for 12 minutes when ambient temp less than 30. Works perfectly and no increase in KWH use compared to before jumper cut. Default is defrost to 47 degrees when ambient temp >30, regardless of whether J2 is cut. In AM when ambient temp >30 unit is heavily frosted. Per manual and discussion with installer have jumped TST to Test Common briefly to increase board timings, then jumped test common to FRC-DFT and unit defrosts. Installer changed defrost board and put in new sensors, checked charge and system operation and said there is really nothing else to do except manually defrost at the defrost board (turning on the cooling cycle at the thermostat also works, and does not turn on the resistance heater which is normally turned on to keep the house warm during the autodefrost cycle). Cools the house a little but works. I don't think the defrost cycle stays on long enough when ambient temp >30. Any suggestions how to proceed? I am not a DIY on this.