why is heater cold on just driver side on my mitsubishi eclipse 2000 gt

sounds like the actuator blend door is not opening all the way

It's because of the way the heater core in these cars is mounted. It seems to happen to everyone at one point or another. You'll need to completely flush the heater core in order to restore heat to the driver's side vents, check out this article on Club3G dot com. Gives a great description. If you don't have time, make sure that the folks at the auto shop read the article, as a simple flush won't do the trick! Good luck! :) http://www.club3g.com/forum/maintenance/154515-get-your-heat-back- right-way-flush-heater-core.html