Arrived to perform a dual maintenance. Controlled the system through the thermostat and set the system to heat. Measured a temperature rise and performed combustion analysis to ensure the system is heating efficiently. Verified operation of all mechanical and electronic components. Checked blower for cleanliness and to see if there is any play in the bearings. Verified operation of the humidifier. Checked heat exchanger for damage and evaporator coil for cleanliness. Switched system over to cooling. Measured a temperature split between return and supply air. System is cooling perfectly at 20 degrees. Moved inspection outside to the condenser. Upon opening the condenser electrical cabinet found a mouse nest. Shorted out one of the wires for call for cooling and cooked the thermostat. Installed a new thermostat. Tested system operations from the thermostat and got back to the cooling part of the maintenance. Checked coil for cleanliness and excessive vibration. Verified operation of all