DESCRIPTION
The air intake control system is a thermostatic air cleaner assembly which maintains uniform air temperature entering the carburetor(s). The incoming air temperature is maintained at approximately 100°F (38°C), regardless of outside air temperature. This permits more precise tuning and balancing of carburetor(s).
The air intake control system helps control Hydrocarbon (HC) and Carbon Monoxide (CO) emissions. It also permits better fuel atomization for more complete combustion. The air intake control system consists of the air cleaner, outside air intake hose, hot air hose, air control diaphragm, temperature controlled air bleed valve, air intake control door and combined vacuum check valve with fixed orifice.
OPERATION
During cold engine operation, below 100°F (38°C), bleed valve is closed. Manifold vacuum builds to allow air control diaphragm to exert vacuum pressure which pulls up on valve door. Valve door rises, permitting heated air from around exhaust manifold to enter air cleaner (outside, cold air is blocked).
During normal engine operation, above 100°F (38°C), bleed valve is open and manifold vacuum bleeds out. Air control diaphragm no longer has vacuum pressure and internal spring pushes down on valve door. Valve door returns to down position, blocking off heated air and permitting cooler outside air to enter air cleaner. A check valve is used to prevent vacuum pressure loss during periods of wide-open throttle operation. A fixed orifice prevents rapid pressure changes at diaphragm. It also allows smooth operation of valve door.
Scheme 9
COLD ENGINE TESTING
Remove air cleaner cover and filter element. With engine cold, start and run engine for about 5 seconds. Air control door should rise and remain fully open for at least 3 seconds after cranking.
HOT ENGINE TESTING
- With engine running at normal operating temperature (cooling fan on), remove air cleaner cover and filter. Immediately inspect door position.
- If valve door has dropped to fully closed position (hot air intake blocked off), system is operating correctly.
- If not, disconnect vacuum hose from air control diaphragm. If door closes, replace air bleed valve and retest. If door does not close, check for binding condition and repair.
IMPROPER DOOR ACTION
- If door did not open for at least 3 seconds (did not rise or fall), check for door binding. If okay, check air bleed valve.
- Disconnect and plug hose leading to air bleed valve. Crank engine for about 5 seconds. Air control valve door should rise and remain up for at least 3 seconds. If door rises for at least 3 seconds, replace air bleed valve and repeat test.
- If door does not rise, proceed with testing of air control diaphragm and check valve. Disconnect vacuum hose from air control diaphragm. On Accord and Civic, remove deflector plate.
- On all models, raise air control valve door manually while blocking inlet pipe. Release valve door. If valve door remains up, replace check valve and retest. If valve door drops to closed position, replace air control diaphragm and retest.
