The opening that you are talking about is the exhaust from the motor, air coming out from there is normal. First thing to check is the suction on the unit, remove the grey 2" tubing from the side of the unit, turn it on, see how the suction is there. If there is strong suction, you possibly have a clog or broken pipe in the system. If the suction is weak, that means your filters need a full cleaning, to fully clean the filters, you need to unclamp the motor from the top of the unit, lift the filter assy. out of the unit, be careful, dirt will fall on the floor from it being trapped on the side of the filter. Now, remove the rubber gasket from the filter, make note on the way it is positions, so you put it back on the same way as you removed it. Once it is removed, you can take the soft dacron filter off and rinse it and than put it on the gentle or handwash cycle in the washing machine or do a hand wash in the sink, the moleskin filter and frame should be washed with some detergent and a soft brush, rinsed thoroughly and dried for a few days. Reassemble the dacron filter to the frame and moleskin filter, replace the rubber gasket on the frame holding the dacron bag into position, put filter assy back into unit and reinstall the motor unit, this will renew the proper suction on your Pullman central vacuum. Good luck.