HVAC blowing only from the defroster is the default mode when the HVAC control head fails. Kind of like your transmission going into limp mode and staying in second gear when there is a major failure. You probably need a new HVAC control head.
Take one of the leaky tires off and while slowly rotating it, spray with water and a little bit of dishwasher detergent. Look for bubbles. Make sure you spray the bead area, and the valve stem opening. If you have bead leaks the tires need to be dismounted from the rims and the rims wire brushed on the bead seat area to clean them up.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)