Coolant Vacuum Switch

Remove the valve from the housing and place it in an ice bath below 40°F (4°C) so that the threaded portion is covered. Attach a vacuum gauge and pump to the bottom nipple. Apply a vacuum signal of at least 10 in. Hg. There should be no more than one inch drop in vacuum within one minute on the vacuum gauge. If the vacuum reading drops off more than this, the switch should be replaced.