It is a very long walk but as you leave the bagage claim at A and go down to the pre-security subway tram you can take the cart down the elevator and walk over to C. There is a carpeted path along the route of the whole train network (people run and work down there) the whole loop is close to a mile IIRC.

It will be a long boring walk (over half a mile) but it will get you where you need to go. I've seen people pushing carts down there before.