To troubleshoot a Trane split system, check the circuit box and ensure it is in the "on" position. Once confirmed, set the thermostat to "fan" and listen for the noise of the fan. If the fan isn't making noise, that may be the problem.
If the fan works, then check the outdoor unit to ensure it is free of debris and that it is plugged in properly. Outdoor units may malfunction if debris blocks the airflow. Pull out the unit's filter and clean or replace it if necessary. The lack of airflow may occur because of a dirty coil that causes the system to freeze. Look for water beneath the unit and feel for cold spots on the unit. In this case, a service call is necessary, and it is important to turn the unit off in order for it to defrost.
Check the gas valve and all gas connections, as the gas may have been turned off or leaking. If the unit produces no heat or is not cooling correctly, double check that the thermostat is set to the right temperature. Units that produce only hot air when the thermostat is set to cool typically require a Trane Comfort Specialist for repairs.