I have a Trane XR14 heat pump (demand defrost). I found some extended performance charts for it on the forum here. It seemed to be underperforming by about 20% based on the delta T even taking into account the lower outside temperature. It has been kicking into defrost when there is not very much frost on the coils. Also it will frequently defrost about a minute after starting up. I had the local HVAC company come out to take a look. The tech checked the charge and said it was low and added some refrigerant. Outdoor ambient was 25 degrees F and he had his gauges hooked up but he didn't evacuate the charge and weigh it back in. Now the unit seems to be defrosting even more often (every 15-20 minutes and very little frost on coils). Is it possible it was slightly overcharged and he made it worse? It looks like my delta T is a couple degrees lower now than it was before. I know an undercharge can cause the outdoor unit to ice up quicker but I could not find any information about an overcharge causing it to trip into defrost more than needed.
source https://hvac-talk.com/vbb/showthread.php?2223274-Cold-weather-charge-and-defrost-behavior-if-overcharged&goto=newpost
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