Mechanically Controlled Thermostatic

Preferred Method
1. Remove air cleaner cover and components necessary to observe position of duct door.
2. With engine cold and ambient air temperature less than 105° F, the duct valve should be closed in the heat on position (closed). If duct valve is open, cool thermostat by spraying with Refrigerant 12. Do not spray refrigerant with engine running, as any refrigerant drawn into the carburetor and burned in the engine will produce poisonous phosgene gas. Conduct this procedure in well ventilated area.
3. Place a magnetic based thermometer (Rotunda T75L-9601-A or equivalent) as near as possible to the thermostat and reinstall air cleaner cover without wing nut. Start engine and allow to idle.
4. As engine warms up, observe duct valve door. When duct valve door opens (heat off position), remove air cleaner cover and note temperature reading.
5. Temperature reading should be about 130---150° F. If not, repair or replace components as necessary.
Alternate Method
1. With duct assembly installed, engine cold and ambient temperature below 100° F, the valve plate should be in the heat on position.
2. If plate is not in the heat on position, check for interference of plate and duct which may cause plate to bind.
3. Remove duct and valve assembly. Immerse assembly in cool (below 75° F) water so that thermostat capsule is covered with water.
4. Raise water temperature to 100° F, allowing 5 minutes for stabilization, and observe valve position. The correct position should be in the heat on position.
5. Increase water temperature to 135° F, allowing 5 minutes for stabilization and observe valve plate. The plate should be in the heat off position.