Strange Climate Control Problem

[RC2007]

I am having an odd problem with my 88 300SE. It has a new climate control unit. The push botton operation as well as the thermostat works just fine, the AC compressor kicks in and circulates but the blower motor which works fine on all settings will only operate when the car is in the on position but not running. Basically the minute you start it, the blower stops working. It would seem that the AC compressor and the Climate control unit can be ruled out. I would also assume that the blower motor is fine as it does function and well while the car is on but not running. Any suggestions?