Hi everyone. Nice to find this forum. I recently have problem charging a heat pump that has a relatively small indoor coil. I charged the unit per rating plate using the subcooling method in cooling mode. For some reasons, the subcooling is not very sensitive to the charge. I had to add 2 lbm to increase 2 °F subcooling!!! I ended up adding lots of charge to the system to get to the rating plate pressure. The unit seemed working fine in cooling mode. However, when the unit switched to heating mode, I noticed a significant high head pressure, like 550 pisg at 47 ambient. I removed lots of refrigerant out to get the pressure below 400 psig.
I am thinking the problem is the indoor coil is too small for this outdoor unit. Does anyone know of any other way to charge this kind of system?