Performed preventative maintenance for heat pump system. Inspected all the electrical components. Confirmed proper high and low voltages. Customer was stating that the unit wouldn’t keep up in heat mode so they ran it in emergency heat. Explained to the customer how the programmable thermostat works since they didn’t understand why it said temporary or hold on the screen. I set the system in a permanent hold to keep the operation simple. Ran system in standard heat pump mode and had a supply temperature of 105° with a return of 75°. Chud performed an air duct cleaning today and replaced the 16x20x1 air filter. System is operating properly at this time. System is 11 years old so I explained the average life span of this type of system as well as what to be ready for as it gets near the average life expectancy for a heat pump.