The inlets below are usually NOT COMPATIBLE with ALL Kenmore PowerMate Central Vacuum Systems. Compatible ones will look like the ones below. If they don't then they are the proprietary valve with a 1-1/4 inch diameter opening. Kenmore inlets with 1-1/4 inch openings are no longer available, but with some hard work the inlets can be updated to modern ones following these steps.
Not all systems are the same so not all instructions will apply. Some creativity may be needed. You should not need to cut open your wall to do this. The goal is to remove the old faceplate and backing plate, put in new ones and feed new pipe into the new backing plate connection. First start with cutting the pipe in the wall, but cut it as it exits the wall in the basement or attic. This is where you will be tieing in the new pipe line. After cutting the pipe, sawzaw the backing plate free so it can be remove from the wall, with the old pipe attached, or pushed out of the way. Use the new backing plate to mark the drywall around the old hole, and cut it so the new backing plate fits snug in the hole in the wall, especially the top and bottom of the backing plate. Be sure to remove the nailing flange on the plastic backing plate. Then glue (using regular PVC glue) a new tight 90 degree elbow on the backing plate and feed the low voltage wire through the top or bottom of the backing plate. Attach the low voltage wire to the new faceplate. Put the backing plate with 90 into the wall with the 90 looking toward the route of the pipe. Then put the new inlet faceplate into the backing plate while sticking your fingers through the inlet to hold the backing plate. Screw the faceplate into the backing plate with the included screws. The faceplate and backing plate are now pinched solidly on the wall. Next, run a new pipe line. Mmeasure and glue the pipe from the attic or basement into the new 90 on the new backing plate. Then use adapter #507P2 to go from the smaller diameter Kenmore pipe to the modern larger (2 inch outer diameter) pipe you just glued in. Click here to see a list of supplies to upgrade Kenmore inlet valves.