Arrived at customer’s house for system inspection. On arrival customer show me to air handler unit and upstairs storage space. Started unit in cool mode but air was coming out warm. Went down to condenser and found no power was being sent to the O wire. Went to thermostat and confirmed. Unit was in cooling mode. Unit was in cooling mode. Went through thermostat and reset settings. Unit now working fine. Thermostat most likely lost power and was not set up correctly when power returned. Checked inside air handler and UV light was passed. Change day. Suggested customer upgrade but customer only wanted to change bulb this time. Change bulb customer happy. Inside home has a smell confirmed by myself and the customer. Talked to customer about oxidizer option. Let customer know changing the UV light would not be a solution to this problem. Customer will consider oxidizer. Sent estimates to customer. Sent customer options for UV light install. We’re customer changes. The filter is very dusty