RepairPal Certified shops can diagnose and repair your 1999 Mazda 626. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
I did find online that on a 98 626 the dash requires major disassembly, evaporator removal to get to the heater core. Yours may be the same. Try this link:
http://bit.ly/autozone_repair_info.