hey, how are you ?
here are a ew things that could be causing you sorrow
1.) Check your vacume to ensure that it isnt clogged anywhere
2.) before your compressor and after the filer, this part is where the suction takes place, check to see that it isnt clogged or that it isnt broken...
3.) check your packing (diapharam) in the vacume oto see if it ruptured(has a hole or broken)
4.) Check for lears on the vacume, basically run a pice of paper all over it and see if it is pulled to the vacume.
Once air is coming out the back, it means the compressor is working, but it alos means that the vacume is clogged, or a compartment that is u\supposed to be sealed is broken, or it has a leak somewhere..
My bet is that it is clogged somewhere, take it apart you will find it..