Defogger Switch Test: MPV
Remove climate control unit, leaving connectors connected. Turn ignition on. Measure voltage by backprobing between climate control unit connector terminal "H" (Blue/White wire) and ground. See Fig 1 . With switch on, voltage should be zero. With switch off, voltage should be battery voltage. If voltage is as specified, switch is okay. If voltage is not as specified, check instrument cluster and wiring. If instrument cluster and wiring are okay, replace climate control unit.