System can handle a 18x20x1 filter at the air handler filter rack. Customer is currently only using a washable filter in the bigger return but nothing in the bedroom returns so air is not fully filtered Completed single system cooling maintenance. Cleared and tread rain line. Checked all electrical components on indoor unit. Checked all electrical components on outdoor unit,cleaned coil and checked charge. Found system low on r22 refrigerant with a low temperature drop across the indoor coil. Customer approved to a on pound of 407 refrigerant. Barge improved and got above freezing. Discussed issue with us timer and leak search options. Also discussed change out options. Customer wants to go with basic repairs at the moment.