Auto Repair Help
┬áMARK’S CORNER – AUTO REPAIR HELP

THERMOSTATIC AIR CLEANER (TAC)
by Mark Davidson

Troubleshooting a car’s emission system often involves inspection of the thermostatic air cleaner (TAC system). The TAC is used to provide warm air to the air cleaner during cold start up. This helps to improve cold engine performance and reduce automotive emissions by providing better fuel vaporization. The TAC system is primarily used on carbureted and throttle body injected vehicles.

The typical TAC system uses a vacuum motor to actuate an air flow TACdoor, located in the air cleaner inlet. The vacuum motor is operated by a signal from a thermostatic switch located in the air cleaner assembly. Warm air is supplied to the air cleaner via a hose that connects from a shroud mounted on the exhaust manifold, to a port on the underside of the air cleaner inlet. During cold engine operation, the actuator closes the air flow door and warm air is drawn into the engine from around the exhaust manifold (take special note of this during a diagnosis of the TAC system). As the engine warms up, the vacuum signal is removed from the actuator and the door slowly opens to allow cooler air to enter through the air cleaner inlet, while at the same time, blocking warm air from the exhaust manifold.

Some TAC systems do not use a vacuum actuator to control the air inlet door. Instead, a sealed actuator containing wax is used. When the engine is cold, the wax solidifies and contracts, causing the door to close. As the engine warms up, the wax liquefies and expands, placing pressure on a piston that is used to actuate the door. The TAC system functions well to aid in cold start up. However, if the air cleaner door were to stay in the closed position after the engine reaches operating temperature, lack of power and hard starting could result. Visual inspection of the TAC system can usually determine if this is the cause of these symptoms. If you are doing the auto repairs yourself or if you have hired your local auto repair mechanic to do it for you, the first step should be to visually inspect the TAC system.

(Mark gave up on sports when the Browns left Cleveland and now spends his Sundays working under a shade tree in the back yard tuning his son’s soap box derby car.)

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5 Comments on "Thermostatic Air Cleaner"

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Chris
4 years 4 months ago

Can a open air cleaner be used on a 2.8 TBI

3 years 4 months ago

Thank you for this information. Moving forward, we’ll always inspect our thermostatic air cleaner.

[…] vehicles. Hmmmm I learned something new. Thought they were only used on carbureted engines. Click–>Thermostatic Air Cleaner ? Auto Repair Help The part I thought you may have been missing is called a heat stove on the carbureted engine. It […]

ROB MINDRUP
1 year 1 day ago

MARK, ON MY 1988 GMC SIERRA K-1500 W/ 5.7LITRE V8 I HAVE THE WAX PELLET ACTUATOR, (THERMAC) THERMOSTATIC AIR CLEANER. THE EMISSION MANUAL STATES THAT THE ACTUATOR ASSY. CAN BE REPLACED IN THE SNORKEL AIR INTAKE. THE PLASTIC THAT HOLDS THE WAX PELLET ACTUATOR IS SECURED BY TWO RIVETS AND A PART # 25095945 IS STAMPED INTO THE PLASTIC. MINE IS STUCK CLOSED! I CANNOT FIND A REPLACEMENT ANYWHERE, NO ONE EVEN SAYS THE PART # IS GOOD. SEEMS A PART # 25097956 IS FOR THE ENTIRE AIR CLEANER. ANY HELP FINDING THIS WAX PELLET ACTUATOR WOULD BE GREATLY APPRECIATED.
THANKS, ROB

Eric
25 days 19 hours ago

i have a 1998 gmc 1500 truck 2wd and i am getting trouble codes P0420, p0430 AND p0440 ALL EMISSIONS I GOT THE CAT LOW EFFICIENCY BANK 1 AND 2, I PLAN ON REPLACING THE CAT…. BUT THE NO FLOW DURING PURGE IS HAVING ME THINK TO REPLACE THE PURGE VALVE COULD THIS FIX MY PROBLEMS OR IS THERE ANY OTHER TESTING I SHOULD DO BEFORE REPLACING THESE PARTS…. THANKS

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