An inoperative heated air inlet system (thermostatic air cleaner) can cause several engine performance problems. If the air cleaner flap remains in the OPEN POSITION (cold air position), the engine could miss, stumble, stall, and warm up slowly. If the air cleaner flap stays in the CLOSED POSITION (hot air position), the engine could perform poorly when at full operating temperature.
Heated air inlet system maintenance
The heated air inlet system requires very little maintenance. Generally, you should inspect the condition of the vacuum hoses and hot air hose from the exhaust manifold heat shroud. The hot air tube is frequently made of heat resistant paper and metal foil. It will tear very easily, Fig. 32-7 A. If torn or damaged, replace the hot air tube.
Testing heated air inlet system
For a quick test of the heated air inlet system, watch the action of the air flap in the air cleaner snorkel. Start and idle the engine, as shown m Fig. 32-7 A. When the air cleaner temperature sensor IS cold, the air flap should be closed. Place an ice cube on the sensor if needed. Then, when the engine and sensor warm to operating temperature, the flap should swing open.
If the air cleaner flap does not function, test the vacuum motor and the temperature sensor.
To test the vacuum motor, apply vacuum to the motor diaphragm with a hand vacuum pump or your mouth, Fig. 32- 7B. With the prescribed amount of suction, the motor should pull the air flap open. If it leaks or does not open the flap, replace the vacuum motor. Recheck heated air inlet system operation to make sure the air temperature sensor is working properly.
To test the thermo-vacuum switch in the air cleaner, place a thermometer next to the unit. With the sensor cooled below its closing temperature, apply vacuum to the thermo-vacuum switch. It should pass vacuum to the vacuum motor. Then, warm the thermo-vacuum switch to its closing temperature. A heat gun (hair dryer) can be used to heat the unit. When warm, the switch should block vacuum and the vacuum motor should open. Replace the thermo-vacuum switch if it fails to open and close properly.