JIm McCarthy

I just picked up a 2000 Suburban 1500 LT 5.3 w automatic climate and heat and a/c in the rear. I am getting no heat at all. The dash control unit all lights up as expected, The only part of the system that is working is the rear blower motor which blows cool air at all times on high speed. The front blower motor is not getting any power. I unplugged it and tested with a voltmeter. The previous owner had been having problems with the heat. He said he had the heater core "professionally checked" and that it is good. He recently bought a new dash control unit off ebay, installed it, and said he had good heat for a while.I do not have any sophisticated scan tool, just a $25 code reader and a volt/ohm meter. Any ideas on how to get this heat working? Thank you.
Also I checked all the fuses in both fuse boxes. All good.
I checked the fan resistor and there was no power going into it regardless of control positions. I pulled the dash control unit and discovered that the wrong one had been installed. Next I obtained the correct new dash control unit, installed it, and now had power going into the resistor. But no power came out of the resistor at any time. I figured the resistor was bad. Si i installed a new resistor. Still no power coming out of resistor no matter how I set the controls. Any ideas on how to proceed from here? Thanks