Homeowner informed me that the AC was not keeping up with set temp on thermostat- mainly upstairs. Upon arrival, I entered mechanical room. AC was running, recorded return and supply temps, checked filter, and checked damper motor. Upon inspection of outdoor unit, noticed outdoor coil was very dirty. Liquid line was very hot due to lack of airflow. Recommended outdoor coil cleaning. Homeowner decided to not have the service done at this time.