Jeeper  Adventures Under the Hood  Jeeper

What's All This Stuff in the Air Cleaner?

1. Referred to as TES (Thermal-Electric Switch) in the service manual, this is a normally closed thermal switch. Sensing the air temperature inside the air cleaner, it OPENS at a nominal 65 F., informing the computer that the intake air is warm.
2. The breather filter for the PCV valve.
3. This temperature-controlled vacuum switch (TVS) is closed below 40 to 55 F. (nominal), preventing the EGR valve and evaporation canister from working when the engine is cold.
4. These are the intake tubes for the Pulse Air system. Notice that the right one is rusty, the result of a bad checkvalve which allowed the exhaust to burp soot and water back into the air cleaner (and carburetor).
5. This second thermal vacuum switch is part of the Thermostatically Controlled Air Cleaner (TAC) System. It controls a trap door in the air cleaner snorkel which routes heated air from the exhaust manifold heat stove into the air cleaner, depending on the air temperature. This provides faster warmup and better cold engine driveability.
1985 Jeep Air Cleaner

- Details -

1. The TES (Thermal-Electric Switch) in the air cleaner is hooked directly to the computer and informs it when the air temperature inside the air cleaner reaches 65 (nominal), at which point the switch opens. On a nice spring or summer day this switch will already be open when you start the cold engine. The computer does not take control of the carburetor until this switch opens AND the Coolant Temperature Switch closes. It remains in what is known as "open-loop operation" until both of these switches do what they're supposed to. During this time it ignores input from the O2 sensor.

2. The Positive Crankcase Ventilation (PCV) system draws fresh air from the air cleaner into the rear of the valve cover, out through the PCV valve (pictured right) at the front of the valve cover, and back to the carburetor where it is drawn in and burned. This inhibits crankcase sludge buildup, and prevents blowby vapors from escaping to the atmosphere. If the PCV valve rattles when shaken, it's probably okay. Occasionally clean the PCV breather filter in the air cleaner. Not shown here is the PCV Shutoff Solenoid, which was removed years ago in a smog-related factory recall, and was replaced by a straight-through hose. If you have the shutoff valve between the PCV valve and the carburetor, you should try to obtain this replacement hose, probably from a dealer.
Note: If oil is blowing into the air cleaner, look at this.
PCV Valve

3. Testing the TVS requires that it be at a temperature below 40 F. or so. Vacuum applied to the inner port should not appear at the other port. When the TVS is warmed to above 55 F., it should be open.
4. The checkvalves in the Pulse Air System prevent backflow of exhaust into the carburetor. If one should go bad (stick open) and allow this, exhaust and water will spit into the air cleaner and be sucked down the carburetor. This is not good. Note that these tubes enter on the inside (clean side) of the filter element. This condition will lead to rust in the tubes, as seen in this photo, and rusty or sooty stains inside the air cleaner (this one has been cleaned). A new checkvalve can set you back about $50.
Rusted Pulse Air Tubes

5. To check for proper Thermal Air Cleaner (TAC) operation, make sure the corrugated hose from the exhaust manifold to the air cleaner snorkle is intact, and the lid is on the air cleaner. Detach the duct from the end of the snorkle. Start and warm up the cold engine while looking in the end of the snorkle. You should see the hot-air trapdoor slowly rise until it hits the top of the snorkle, allowing the engine to draw heated air from the exhaust manifold. Once the engine is completely warmed up, raise the rpms a couple times and let the engine fall back to idle. The trapdoor should slowly drop down until the snorkle is drawing fresh air. If you remove the lid from the air cleaner and put your finger on the small tube sticking up from the vacuum switch, you should feel some vacuum and the trapdoor should quickly close (pull up). When you remove your finger the trapdoor should slowly open (drop down). If things aren't working, check the air cleaner housing vacuum hoses starting at the rear left corner of the carburetor all the way to the vacuum motor itself. Make sure the trapdoor isn't frozen or hanging up.

There is a second trapdoor in the snorkle closer to the air cleaner body. This one should be closed when the engine is stopped and fully open when the engine is running. It's purpose is to prevent fuel vapor from escaping to the atmosphere when the engine isn't running. More details of the TAC vacuum hoses can be found here.

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