Assuming exact cause of failure is uncertain, so a service technician will have to diagnose the underlying mechanical/electrical problem before repairing.
Rooftop unit xxx supplies heating and cooling to the main hallway. The economizer cycle controls are not working properly to provide free outside air cooling. The outside air dampers appear to remain fully closed even when free cooling is available. On a call for cooling, the mechanical refrigeration system will start.
This free cooling condition occurs for much of the year. ASHRAE guidelines stipulate that the economizer cycle should be implemented and working wherever possible.
It is recommended that the economizer damper motor and controls be repaired to ensure that the air handler takes advantage of all free cooling opportunities.
If the controller and sensors need replacement, we recommend simple 'dry bulb' override, which will lock out free cooling (and shut the dampers to minimum position) when outside air temperature exceeds 21°C.
Issues and Concerns
This recommendation is in accordance with Section 6.3 Heating, Ventilation and Air-Conditioning Systems of the ASHRAE Standard on Energy Conservation in Existing Buildings.
Allow $2000 + $100 per ton of cooling capacity. This should cover a combination of electrical and mechanical repairs.