Economizers can provide free cooling when the outdoor temperature is below 60-65 degrees. Keeping these systems fully functional with thorough preventive maintenance testing and completing repairs as required, can save large amounts on electric utility consumption.
This is accomplished by introducing cold, outdoor air by opening a damper and tempering as needed to the space. The electric used to run the fan is needed in any cooling mode but operating in economizer mode saves a tremendous amount by not operating the compressor, which is the biggest electric load in the cooling system.
Economizer operations also prevent wear and tear on the mechanical cooling compressor by not running them in short intervals in cooler weather than they were truly designed for.
Units that do not have economizers are highly recommended to have one installed, if possible. Economizers also provide ventilation by introducing fresh air changes into space, making the indoor environment non-stagnant and breathable.