My 99 LaSabre Blows out hot and cold from the floor and vents when the heater is on, I get weak warm air from the vents on the driver side and strong cold air on the passenger side, I have noticed this happens when the temperature number that is displayed on the control panel flashes repeatedly, Is the control panel going bad or is it the vacuum lines? I would appreciate some help with this. thank you Cliff

 

sounds like the control head may be going out. have a good shop diagnose it. you should be able to get a good used one in the $70 range.