System not running periodically due to clogged drain line. External pan was overflowing water onto the ceiling. Safety overflow switch was incorrectly positioned. Tested it and made sure that it functions correctly. Due to severity of the clog chemical treatment had to be used to clean pvc drain line. Cleaned internal drain pan from slime and growth. Noticed a lot of growth on blower wheel and inside air handler cabinet. Checked refrigerant charge. Tested a system and made sure that is draining well. Customer was notified of the issues and said they will consider replacing system in a spring