System Check
- Check all vacuum lines for connection, cracks or loose fitting and proper routing. Replace or reroute as necessary
- To check vacuum motor, stop engine and unhook fresh air duct. Using a mirror, check position of air control valve inside duct. With engine warm, fresh air inlet should be open and hot air duct closed. Check control valve linkage.
- Disconnect vacuum motor inlet vacuum hose. Install another length of hose to inlet and apply vacuum through this hose to vacuum motor.
- With vacuum applied, again use mirror to check air control valve position. Fresh air inlet should now be closed and hot air inlet open.
- With hot air inlet open (vacuum still applied), pinch vacuum hose to cut off air to vacuum motor. Air control valve should hold position for more than 30 seconds.
- If force of diaphragm spring overcomes vacuum and opens fresh air inlet in less than 30 seconds, replace vacuum motor assembly.
- To check temperature sensor, start and idle engine. As engine warms up, air control valve should slowly open to admit fresh underhood air.