Responded to service call regarding two non-functioning RTUs. Restored operation to first unit by resetting tripped breaker on roof. Second unit in training room had a failed control board despite receiving power; breaker was also off. Third unit in main front room was troubleshooted by jumping connections at both control board and thermostat, which temporarily restored operation. Replaced thermostat but unit still failed to function properly. Recommended follow-up service call with another technician to diagnose potential inducer motor failure.