I turn on my heater( carrier weather maker 8000)and as soon as the Gas lights into the burner the motor turns off stopping warm air being blown but yet the fire is still on .when I turn off the thermostat it then turns off but when I turn on the ac everything is working fine and the motor is running good? Does someone know what could be malfunctioning

I would suggest getting in a tech to look over the wiring. However, it sounds like you may have a fualty control board. Here's how it should cycle. The thermostat call for heat, the draft inducer motor starts, the igniter glows, or sparks, the gas lights, then anywhere from thirty seconds to 90 seconds later, the blower comes on. Then when the stat is satified, and ends the call for heat, the flame goes out, the draft inducer stops, then a while later the blower stops. Really sounds like things are out of sequence on your unit. Time to get a pro in to figure it out. Good luck, and please let me know how things turn out.