I was called to a home in Tucson, Arizona, to service a rheem split gas system. The customer reported that the system was not cooling properly. Upon arrival, I checked the system and found that the compressor was not running. I checked the power supply and found that it was working fine. I checked the thermostat and found that it was set to "heat." I checked the air filter and found that it was dirty. I cleaned the air filter and checked the system again. The system started up and cooled the house properly. The customer was happy with the service.