Contents: Description ⬇ Examination ⬇
Description
1. On Multec models, the air temperature is controlled by a regulator mounted in the air block. When the engine is started from cold, the regulator is closed and the vacuum in the intake manifold acts on the air temperature control valve in the air cleaner assembly. It uses a vacuum booster in the valve assembly to close off the cold inlet air with a flap, thus allowing only warm air from the exhaust manifold to enter the air cleaner.
2. As the temperature of the inlet air in the air block increases, the bimetallic plate in the thermal switch is distorted. The switch is triggered and releases the vacuum in the air temperature control valve. The flap gradually begins to block the warm inlet air. Until the engine has warmed up completely to normal operating temperature, only cold air is supplied to the air filter.
Examination
3. To check the system, allow the engine to cool completely, then remove the air cleaner cover; the flap should completely block the hot inlet air. Start the engine. The flap should immediately rise, blocking the flow of cold inlet air. And then, as the engine warms up, it should gradually fall until it completely blocks the flow of hot inlet air again.
4. To check the thermal switch, disconnect the vacuum control valve pipe from the switch coupling while the engine is running (on the rear surface of the air block). Until the engine is warmed up, a vacuum from the intake manifold should be felt at the coupling; after the engine has fully warmed up, the vacuum should not be felt.
5. To check the air temperature control valve, remove the air filter cover; the flap should completely block the flow of hot inlet air. Disconnect the vacuum tube of the control valve from the switch coupling on the rear surface of the air block, and suck air from the tube with your mouth; the flap should rise, blocking the flow of cold incoming air.
6. If any component is faulty, replace it. This means replacing the lower air cleaner housing if the air temperature control valve needs to be replaced, or replacing the air block housing if the thermal switch needs to be replaced.
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