In addition to the air pump you should have a vacuum solenoid that controls a diverter valve. Follow the large air pump hose to a device ( diverter valve ) that will have a small vacuum hose, follow that vacuum hose to a solenoid valve, check the electrics here.

Also, pull the vacuum hose from the diverter valve and install a vacuum gauge, if the air pump runs the solenoid should trigger some of the time and you should see vacuum.