Thermostatic Air Cleaners -- All Models: Description
All passenger cars use a system for preheating the air entering the carburetor. This device is part of the air cleaner and maintains the air temperature at a point where the carburetor can be calibrated much leaner to reduce hydrocarbon (HC) emissions and also improve warm-up operations and reduce carburetor icing.
System consists of an air cleaner assembly, integral air control door, vacuum control temperature sensor, vacuum motor, heat shroud (on exhaust manifold) with connecting pipe and vacuum hoses. Some models use additional controls, such as vacuum traps and cold weather modulators.
Some General Motors 151" 4-Cylinder engines use a thermostatic air cleaner system that does not use a vacuum motor to control the air control door. Door is controlled by a thermostatic spring only.