Three Function Trinary Pressure Switch The Trinary Switch protects the system from excessive high or low system pressures, in addition to automatically operating electric radiator or condenser fans as needed for maximum system performance. Trinary Safety Switch Pressures: Low is off @ 28psig - and on @ 29psig High is off @ 454psig - and on @ 369psig Fan is on @ 227psig - and off @ 185psig Made in the ...