It sounds and feels like the relay is in the part where the button is located. You should be able to hear it click when the button is pushed. There's one screw that holds the dash on, then spring clips. If you're not hearing that relay, then maybe it's just loose or it's gone bad. I didn't see a fuse assigned specifically to the heaters at the dash or under hood fuse blocks, but may piggy back another 12vdc line. I have a service manual I can look at if the relay seems good.
ic.