Today I had the pleasure of conducting maintenance on a 4 year old Carrier condenser unit with a 3 year old RUUD air handler. Upon arrival , homeowner stated the system has been working fine. He understands the upstairs system wasn’t under a maintenance plan but voiced that the room it cools stays hot. I started by verifying system cleanliness and found the ducts dirty and in need of cleaning. I then verified all amps, temps, and pressures. I found the system operating well within manufacturer specifications. As a courtesy, I took a look at the upstairs system and found that the thermostat for the room was sharing a wall with the attic. It read 71 degrees in the room on the thermostat but when using my thermal imager, I found the room to be 79 degrees. I shut off power to the system and reenergized. The thermostat read the true room temp. I told the homeowner to monitor the thermostat. All conditions otherwise normal at time of departure.