DESCRIPTION
The air intake control system is a thermostatic air cleaner assembly which maintains a uniform air temperature entering the carburetor(s). The incoming air temperature is maintained at approximately 100°F (38°C), regardless of outside air temperature, to permit finer tuning and balancing of the carburetor(s).
This helps control hydrocarbon (HC) and carbon monoxide (CO) emissions and permits better fuel atomization for more complete combustion. The air intake control system consists of the air cleaner, an outside air intake hose, a hot air hose, an air control diaphragm, a temperature controlled air bleed valve, an air intake control door and a combined vacuum check valve and fixed orifice.
OPERATION
The following is a description of reaction of system components during operation under all engine modes
ENGINE COLD (BELOW 100°F)
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).
ENGINE HOT (ABOVE 100°F)
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 outside air to enter air cleaner.
CHECK VALVE
This valve acts to prevent vacuum pressure loss during periods of wide-open throttle operation.
Sectional View of Air Intake Control System (Accord & Civic Shown; Prelude Similar). Scheme 9
FIXED ORIFICE
This unit prevents rapid pressure changes at diaphragm. It also allows smooth operation of valve door.
COLD ENGINE
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
- With engine running at normal operating temperature and cooling fan on, remove air cleaner cover and filter. Immediately inspect door position.
- If valve door has dropped to a 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 respond as indicated above (did not rise or fall), first check to see if door is binding. If okay, then 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 it does, replace air bleed valve and repeat test.
- If door does not rise or remains open, 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 and, 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.
