Performed preventative maintenance for a Heil heat pump model. I observed the system starting normally. The supply temp is at 125°F. Amp draw for the blower motor is at 1.5. I observed the system shut down normally once it reached the desired temperature. All electrical components are intact and operating properly. Blower wheel is clean. Evaporator coil's are dirty due to the air filter not being changed. Performed evaporator coil cleaning. Replaced the air filter size 20x20x1. The refrigerant pressures are within normal range. The amp draws for the fan and compressor are within normal range. The condenser coils are clean..