Performed cooling maintenance on one heat pump system. Checked all electrical, mechanical and performance of the system. While performing maintenance, I found that the system is low on R410-A refrigerant, and the system does not have a water safety switch. The evaporator coil is very rusted, but I was unable to locate a leak at this time. I sent over the estimate for the repairs as well as an estimate for replacing the evaporator coil. No other major issues were found. System is running at this time.