The heater air plenum chamber (18471) is located under the instrument panel (04320) on top of the heater core housing. For servicing the heater air plenum chamber , A/C plenum vacuum harness (18C581) , and plenum doors, it is necessary to remove the instrument panel . It is not required to remove the instrument panel to service the vacuum control motors (18A318) attached to the heater air plenum chamber .
1. Remove instrument panel, and steering column.
i would suggest purchasing a chiltons or haynes manual from an autozone, or ebay.
heres a link to one on ebay. for $23 with free shipping. these are getting harder to find.