How to Troubleshoot a Thermostatic Air Intake System

You may not have heard much about it, but the thermostatic air intake system in your vehicle is in charge of keeping engine efficiency and hydrocarbons low when you hop into your car and start the engine for the first time during the day. This system, used in many carburated models, operates through a simple vacuum circuit to keep the air entering the air cleaner at a warm temperature. When the thermostatic system fails, your engine misses, stumbles, stalls and performs poorly. We will go through some simple steps to help you troubleshoot your system and find the problem or verify that it is working properly. And best of all, you do not need special knowledge.

Instructions

1

Locate the air cleaner assembly. It is the round or oval case on top of the carburetor unit housing the air filter.

2

Examine the air intake vacuum hoses and the hot air tube under the duct coming out of the air cleaner assembly. Make sure they are in good condition. Replace the hot air tube and vacuum hoses if necessary.

3

Disconnect the plastic air pick up duct from the duct assembly. Make sure the transmission is set to "Park" for automatic transmissions or "Neutral" for manual transmissions, apply the emergency brakes and start the engine. Let it idle.

4

Look through the duct assembly using a small mirror and make sure the heat control door under the vacuum motor is closed. As the engine temperature begins to rise, the door should start to open slowly too. If the door is not operating properly, go to the next step.

5

Turn off the engine and let it cool down. Move the heat control door with your fingers and make sure it is not stuck. If you feel some resistance, apply penetrating oil or lubricant to free the door hinge pin.

6

Inspect the vacuum motor--sitting on the duct assembly over the heat control door--and make sure it is working properly. Disconnect the vacuum hose from the motor and connect a hand-vacuum pump. Apply enough vacuum to the motor to raise the heat control door. If the motor does not hold vacuum or respond, replace it.

7

Disconnect the vacuum hoses from the thermal vacuum valve-underneath the air cleaner assembly-and apply vacuum with a hand-vacuum pump to the valve. The valve should hold the vacuum when the engine is cold. Warm up the engine and repeat the test. The thermal valve should not hold vacuum now. If the thermal vacuum valve is not operating as described, replace it.