Reference Manual

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Chapter 10: Emissions Equipment: THERMAC

Purpose:

A heated intake air system is used to give good driveability under varying climatic conditions. By having a uniform air inlet temperature, the fuel system can be calibrated to reduce exhaust emissions and to eliminate throttle valve icing.

Operation:

The THERMAC air cleaner operates by heated air and manifold vacuum. Air can enter the air cleaner from outside the engine compartment or from a heat stove built around the exhaust manifold. A vacuum diaphram motor, built into the air cleaner snorkle, moves a damper door, to admit hot air from the exhaust manifold, outside air, or a combination of both. Inside the air cleaner is a temperature sensor that reacts to air intake temperature and controls the amount of vacuum going to the motor.

• Hot Air Delivery Mode. When the temperature is below 30°C (86°F), the sensor allows vacuum to the motor and the damper door will be up, shutting off outside air and allowing only heated air from the exhaust manifold to enter the air cleaner.
• Outside Air Delivery Mode. When the temperature is above 55°C (131°F), the damper door drops down and only outside air enters the air cleaner.
• Regulating Mode. Between 30°C (86°F) and 55°C (131°F) the damper door allows both heated and outside air to enter the air cleaner.

Thermostatic Air Cleaner - "VIN 9"

The "VIN 9" applications use a dual-snorkle air cleaner assembly. The added snorkle contains a vacuum motor that is operated directly by intake manifold vacuum. This vacuum motor will start to open at 15.2 kPa (4.5" Hg) and be fully open at 5 kPa (1.5" Hg). The other components of this air cleaner assembly are the same as those used on the "VIN Y" engine.

Charcoal Absorber

The 5.0L, "VIN 9" application uses an air cleaner assembly containing an activated charcoal absorber. It will be permanently mounted inside of the area that contains the air filter element. The absorber acts as a barrier preventing fuel vapors from passing through the air cleaner element and then into the atmosphere.

Results of Incorrect THERMAC Operation

Hesitation during warm-up can be caused by:

• Heat stove tube disconnected.
• Vacuum diaphram motor inoperative (open to snorkel).
• No manifold vacuum.
• Damper door does not move.
• Missing carburetor seal.
• Missing air cleaner cover seal or loose cover.
• Loose air cleaner.

Lack of power, sluggish, pinging or spongy, on a hot engine can be caused by:

• Damper door does not open to outside air.
• Temperature sensor doesn't bleed off vacuum.