This system consists of a bypass device with an adjustable flap, installed on the air filter intake pipe nozzle and providing regulation of the ratio of cold and warm air directed to the carburetor. The position of the device's damper is changed using a vacuum diaphragm, which, in turn, receives force from a temperature-sensitive element located inside the air filter.
The system has a significant impact on engine traction and exhaust gas toxicity during the first few kilometers of a vehicle's travel with an unheated engine.
When the engine is cold, the device's damper completely closes the air filter's intake pipe channel, and only warm air, which has previously flowed around the exhaust manifold, enters the carburetor. As the engine warms up, the damper opens slightly and more and more cold air begins to flow through the intake pipe. When the engine is fully warmed up, the damper opens completely, providing full access to fresh, cold air.
The automatic air temperature control system is designed only to supply warm air to a cold engine, so it is important to check it periodically to avoid engine operation problems after warming up due to the supply of an overcooled or overheated fuel-air mixture.
If the air filter flap sticks in the "no heat" position, the engine will idle unevenly and stall before it has fully warmed up, requiring additional pressure on the accelerator pedal. If the throttle valve sticks in the "heat" position, the constant supply of hot air to the carburetor will create the impression that the engine is out of adjustment.
Technical condition check
Checking the technical condition and maintenance is given in section 2. If there is a need for inspection during routine maintenance, proceed in accordance with the following sequence.
If the ATC valve does not completely shut off cold air after starting a cold engine, disconnect the hose from the vacuum diaphragm on the intake manifold and place your thumb over the opening of the hose. If a vacuum is felt being supplied to the diaphragm, the cause may be a frozen or stuck flap or rod inside the air filter intake pipe. If you have a vacuum pump, apply vacuum to the throttle actuator to ensure it is working properly, after disconnecting the standard vacuum hose. If the vacuum from the pump does not cause the temperature control valve to open, and the valve opens freely when the vacuum hose is properly connected, replace the vacuum diaphragm.
If there is no vacuum on the diaphragm in the above test, check the hoses for cracks, pinches, and the reliability of their connections.
If the hoses are not clogged and are in good condition, replace the temperature-sensitive element located inside the air filter housing.
Replacement of parts
Vacuum diaphragm of the air filter
Disconnect the vacuum hose from the diaphragm.
Remove the limiter screw, unhook the rod and unscrew the diaphragm from the air filter housing.
When installing, insert the diaphragm into the air filter housing, screw it in, attach the rod, and screw in the limiter screw.
Connect the vacuum hose.
Temperature sensitive air filter element
Remove the air filter to gain access to the area underneath.
Note the location of the vacuum hoses and disconnect them from the temperature sensor.
Carefully mark the position of the element, as this is exactly the position in which the new element must be installed. Lift and remove the element from the air filter housing.
Install the new element in exactly the same position as the removed one, connect the vacuum hoses.
Install the filter element and the top filter cover.