I lost heat last week for no apparent reason. I replaced the monovalve and it works, and I am getting vacuum from the whit line from the servo, but apparently the other white line that t's in near the servo isn't holding the vacuum. I can manually open the monovalve and still have no heat. The only thing I have changed in the last week is i had to take the AC belt off and haven't replaced it, but I can't see why that would matter. Any ideas??