GM’s THERMAC System. How Does it Work?

The thermostatic air cleaner system, also referred to as the ThermAC System, was a unique component of the Controlled Combustion System, or CCS, for most of the 1970s.

Its only purpose was to help reduce exhaust emissions by using carburetors calibrated lean as well as retarded ignition timing. This also required higher engine temperatures to burn condensed fuel vapors in the cylinders. This was accomplished by reducing the "quench area" near the cylinder walls.

The ThermAC air cleaner system used a heat stove placed on top of the closest exhaust manifold. This moved hot air into the carburetor via a metal tube.

The main components of the ThermAC System included a temperature sensor unit, the vacuum diaphragm assembly, a damper door or flap near the entrance of the snorkel tube, and connecting vacuum hoses.

The thermostatic system kept the air entering the carburetor at 100°F or higher, which allowed GM to calibrate carburetors on the lean side to reduce hydrocarbons. Plus, higher air temperatures also helped minimize carburetor icing and cold-engine starts.

I am not sure how effective this emissions control system was, but my guess is that its benefits were marginal.

Thank you for watching! 🙂👍🏻

======================================

CORVETTE PRODUCTS (sponsored)

76 Vette Assembly Manual: https://amzn.to/2GBuHrd
68-82 Corvette Manual: https://amzn.to/3devEEW
How to Restore Corvette: https://amzn.to/35B6L0R
68-82 Vette Resto Guide: https://amzn.to/2QvvIG

======================================

DISCLAIMER: Even though I like to wrench on my Corvettes and most of my videos are of a how-to nature, I am not responsible nor liable should you decide to follow my musings on the subject.

I am a self-taught DIYer. If videos appear to give technical how-to advice, that is not my intention.

Working on a vehicle can be dangerous. If you're not confident, qualified, or lack the tools to do the job correctly and safely, hire a mechanic.


#corvettec3 #c3 #c3corvette