Acceleration Enrichment Module: Description and Operation

Fig.17 - Pressure Differential Switch:

The pressure differential switch (PDS), Fig. 17, incorporates two chambers which are separated by a diaphragm. The diaphragm is preloaded by a coil spring and has a bleed hole which will equalize the chamber vacuum after a delay period.

Fig.18 - Thermal Control Valve:

The pressure differential switch is connected to the intake manifold by the thermal control valve (TCV), Fig. 18. It opens the vacuum line at temperatures below approximately 127 F. When the accelerator pedal is depressed, vacuum decreases in the manifold and in the pressure differential chamber. A higher amount in the other chamber closes the pressure differential switch, until the diaphragm bleed hole has equalized the pressures. The switch will be closed for approximately 1/4 of a second during a low pressure differential and approximately 1.5 seconds during a high pressure differential.