Is your AC coming out of the defrost? This is how you can tell if the vacuum system has a leak. I would check the back of the hubs where the hoses connect. It is a piss poor design, as they simply slide over a nipple, the end gets split and therefore leaks so no vacuum build up. Just cut off 1" or so to get to healthy material and reattach the lines and see if this resolves your problem. if the vacuum pump shuts off it means you don't have a leak. Could also be hub seals as well, but start with the simple stuff.
NCH