We have a 99 cavalier with the 2.2. We got the car as an abandoned vehicle so we know nothing of the cars history to start with. Motor was knocking so we got a new motor and put it in. As we were getting the motor warm and filling up the antifreeze we noticed it was leaking so we removed the dash and replaced the heater core. Once that was all back together and car was full of antifreeze again we went to turn on heat to check it out. blower wouldnt come on. We pulled the blower motor and tested it. Came on just fine. Replaced resistor and still got nothing. Figuring it would be in the switches we got new heater controls and still got nothing. Pulled dash again and started checking the grounds. Grounds where all fine. If you ground the light green wire that runs from the heater controls to the Microprocessor in the instrument cluster then to the ECM the fan motor will run in all positions with the ac button pressed. If you turn the ac button off the fan will only run in the circulate and defrost positions, but turns off with the switch on the controls. At this point im at a loss, I dont know if it would be the instrument cluster, ECM, or the wiring. Any help is greatly appreciated.