I just relocated from Florida and my brand new Carrier Infinity system to NC with a 20 year old Rheem RPKA-036JAS and RBHA-17J155FBA. Want to change it out after being spoiled by the new technology but still working cost comparison on upgrading and keeping it. Anyway my question is about the large line (low pressure?) froze upon me one night. It was the first night the cooling had to run and when I awoke the outdoor unit was still running and the air handler was off. I turned the T-stat fan to ON and it blew, I bumped down the Temp and it blew as well. When I went outside the large line had a coat of ice around it. Any ideas on what would have caused this? I have used it since with no issue but I am not a huge believer in things fixing themselves. Also any idea on this setups efficiency?