2003 Chevy Astro blower motor

2003 Chevy Astro Van. I have a 03 Chevy Astro Van. The rear air conditioner is not working. The blower motor is good, I hooked it up to 12 volts and it works, when there is a load or the blower is hooked up the voltage drops down to 0 volts. The switch is good, the fuse is good and the rear condenser is getting cold, it's just not blowing out air. Is there a relay or something that is bad? All speeds for rear blower do not work, the front works great. Thanks Jim