If you have no heat at all but the controls work on the o2 gallant?

If you have no heat at all but the controls work on the o2 gallant?
By "all the controls" I'm assuming you mean interior switches, dials etc.
Your problem could be a bad control valve on one of the heater core hoses not allowing hot water to circulate thru the heater core. Check the two hoses going into the firewall on the passenger side. If, when engine is warmed and all the controls are set for heat, the inlet hose is hot and the outlet cold, the problem is probably under the dash. Electrical, control valve or plugged heater core.
The heater control valve motor is located below the dash on the passenger side. First remove the glove box, then the lower trim panel. Before removing the lower trim panel remove the center trim around the radio and A/C controls. After removing the lower trim panel, the heater control valve motor is on the left side underneath the automatic compressor controller, connected to the heater control unit.
When switching from heat to cold the valve motor should be visibly operable.
FYI....HEATER CONTROL VALVE FAILURE HAS BEEN AN ONGOING ISSUE WITH MITSUBISHI...LOTS OF COMPLAINTS....$300-$400 REPAIR COST AT A DEALER.
Hopefully a Mazda tech will respond with a better answer.
Good Luck