I was working on this same problem last night. I actually ripped apart the pump to look at the motor. The problem with the pumps is the brush holders are made of plastic. They melt and cause the carbon brushes to go askew. Then they wear out and get stuck from all the dust and junk in there. So they don't make good contact with the armature. This will give you intermittant results. Here is how you should troubleshoot this:

First go get two alligator clip test leads and a piece of 16gauge lamp cord from Radio Shack of Ace Hardware.
Remove pump from car.
Put the alligator clips on the terminal lugs on the pump then observing polarity (printed on pump) touch the wire to the battery.
It should go like hell. Start and stop it a few times to make sure you don't have a dead spot. Make sure wind comes out of the pump to verify the nut didn't come loose on the fan blade.

No go ? Get a new pump. Good? remount and connect pump.

Next dissconnect your neg. battery cable.
Remove the RCM module, pry off cover, and set it on a piece of cardboard assuring it can't slide around and touch metal.

Reconnect Neg. battery cable.
With a pencil push down on the first relay.

Does the pump go? If yes, then the problem lies with the vacuum system that opens the valves on the manifolds.
If no, then the problem is either the relay contact (just clean it), fuse, or wiring in between.

Try that first and I can help with the vacuum stuff if need be.

Remember to disconnect battery again when putting the RCM back.