Inconsistant blower speed?

Beginning to find out the drain on my electrical systems is related to the HVAC system. Found a loose connection in the module cluster and also a broken resistor for the heat/cool switch. Question is this, running in drive position at a stop light start to loose power (below 14V but not less than 12V) and the air volume changes and at running speeds I noticed a pitch change in the volume of air from the vents. Does this sound like the resistor under the hood or something like the fan motor itself? I have the part (resistor for fan speeds) on order at NAPA but if dosn't sound like the problem I'll start looking at the motor....also what is RPM idle in park and in drive at a stop?

Same thing happened to me. I had the rear defoggers on. As soon as I turned them off, the blower motor doubled in speed and the voltage went back to 14v. Now, I did read somewhere that there was something wrong (bad connection or bad wire) with the power wire going to the alternator. If I find it, I will post it. I'd also check and make sure that you have a good ground also.