Equip your semi with air reliable AC that activates when needed, with the OTR 12V 70A 4-Terminal A/C Relay Switch with Expertise Built In™. Following directions from a user, this replacement relay sends electricity to the compressor clutch to engage the air conditioning system. Evidence of a bad relay include unexpected AC shutdowns, clicking noises, or an unresponsive switch. The air conditioning and heating system in heavy duty trucks has a major impact on drivers’ safety and comfort level. Whether you are looking for A/C compressors, condensers, driers, freon, or blower motors, FleetPride has the part you need to make sure your air conditioning and heating are well maintained. Keep your heavy duty fleet operations working as productively and efficiently as possible by finding the right air conditioning and heating part for you. FleetPride is your First Click in Heavy Duty®.