Trane heat pump

[brad_monty10]

Had a Trane heat pump yesterday off in code 4 , hard lock out due to lock trip , inspect outdoor coil small amounts frost , reset and test defrost cycle all works properly , run unit outdoor temp 30 F , suction pressure 65psi 15 degree f super heat , thing I found weird was high liquid pressure 450 psi , with 50 degree sub cooling , I feel like the unit is over charged but don't understand why the unit randomly locked out of low pressure , anything suggestions greatly appreciated haven't work on many heat pumps in my career so far

[Admin]

You're measuring superheat, does that mean your indoor coil used as an orifice and not a TXV?

I suspect the outdoor unit has a TXV built into it and this is the cause of your problem.  If so you should be measuring sub cooling during a heat cycle.

[brad_monty10]

All measurement have been in heat mode with 30F outdoor temp , outdoor to. , removed bulb and checked operation pressures adjusted with bulb in hand. Another question I have is regarding defrost with forced air furnace as back up. I have noticed on last two units I have worked on is that the furnace fires up on defrost but I have been told on first I installed was to not hook up w from defrost board to the furnace, I feel like it works well to run furnace on defrost helps to add heat to melt coil faster

[Admin]

Defrost mode is essentially just the heat pump running in cooling mode without no outdoor fan.  This is what thaws out the outdoor coil.  Because the indoor coil is now cooling you definitely want to energize the gas furnace or electric elements.  This is how I do it with either Goodman or Lennox.  Otherwise you're just blowing cold air in the house.

[brad_monty10]

It was goodman that told me not to energize the gas furnace

[brad_monty10]

Does anyone have cop chart for Trane 4twr4024 heat pump , going to install outdoor sensor to thermostat , going to try and calculate an economical switch over tenp

[brad_monty10]

Found the unit tripping on low pressure on days colder than -10 Celsius and having around 15 degree evaporator/outdoor coil was making the pressure below the 45 psi pressure switch , install outdoor sensor to lock out compressor at -7