The heated/cooled seats are highly dependent upon air flowing through channels in the seat foam. As the foam ages and wears, it crumbles, filling in the channels and obstructing air flow. Thus, replacing the seat foam can go a long way towards fixing inoperative climate seats.
With that said, however, be aware that an important airbag-related safety device is integrated into the passenger side seat bottom foam. This computer/sensor turns the passenger airbag on/off and may also be responsible for controlling the dual-stage functionality. Thus, it is critical to follow all safety instructions contained in the Factory Service Manual (FSM) for working on the passenger seat bottom. Do not attempt to mess with passenger seat bottom foam unless you obtain a copy of the FSM for your vehicle and review all safety precautions first.