Automatic air damper (Honda Accord 3)

The flap is controlled by a vacuum-actuated valve that is adjusted based on coolant temperature. A separate temperature-sensitive valve controls the flow of coolant through the carburetor heating channels. As the coolant heats up, the flow through the carburetor heating channels decreases and vacuum begins to flow to the flap valve, taking into account the ignition timing. The flap valve is designed as a return diaphragm connected to the flap lever. In addition, there is another temperature-sensitive valve that pushes the idle lever down when it is sufficiently heated by the coolant.

Even when the engine is cold, some vacuum is applied to the diaphragm and excess vacuum is released. During engine cranking, all vacuum is released by the starter solenoid valve, which is activated when the starter motor is running. This valve should only operate when the ignition key is in the START position. A malfunction of this device can cause a difficult cold engine start. The blue/red wire on the main connector of the solenoid control unit, located on the firewall, goes to this starter vacuum release valve.

Checking functionality

1. When the engine is cold, disconnect the hose from the diaphragm valve and connect a hand pump. After locking the ignition system so that the engine cannot start, turn the ignition key to the START position. There should be no vacuum on the diaphragm, since the solenoid valve should be on.

2. Disconnect the hose from the exhaust manifold and pump the diaphragm to vacuum through this hose. The vacuum should stabilize in the range of 102-203 mm Hg, at which the diaphragm should pull the throttle lever.