I have a 2006 2500 Cummins Laramie. My A/C Compressor was just replaced after shorting out. and I replaced the resistor pack. 2 years ago i replaced the door that controls the recirculation of cabin air. And still I am having problems. When I start my truck the fan in the cab may not come on, or if it does the speed is slower than is expected with the fan switch turned to the high position. If I smack the fan-A/C box under the glove box the fan speed will increase. Im just not getting a good volume of cold air.
Any ideas? Thanks

 

Sounds like the blower motor itself has a bad bearing or winding.

 

could also be a bad or corroded connection to the fan blower motor resistor block