Air Vents Stay in Defrost Position
Air Vents Stay in Defrost Position Helpful Information Engine vacuum is used to control the vent position in some vehicles. A simple control valve and vacuum storage tank is used to operate vacuum controlled servos. These servos move various air blend doors inside the air management housing or plenum. Servos are connected to a vacuum source by vacuum hose and utilise a return spring that forces the servo to return when vacuum is not applied. The main engine vacuum is supplied to the control valve on or near the dash. A vacuum check valve is used to stop the flow of vacuum from returning to the engine during low vacuum conditions for example: engine under heavy load like driving up a steep grade. When the engine vacuum supply is lost, the vent control system defaults to the "defrost mode" as a safety precaution. We have listed the most common reasons for this condition below. Best Practise Avoid using tape or glue to repair a vacuum line Step by step guide on h...