heater blower motor
 

Sorry, I inadvertently posted this in the first generation site:

All of a sudden my AC blower started making a hell of a vibration/racket on high speed. A few days ago, I distinctly smelled "mouse smell" inside the cab. Since the blower motor is only a year old, I figured a mouse had gotten in there, which it had along with one baby (yes, I searched for more). After pulling out the newly dead mice, I sprayed everything with chlorox and reinstalled the blower motor. Now, no matter where I set the blower vent control, I only have air blowing out the defrosters. I may have inadvertently pushed on the interior vent door located just inside and above the blower motor while cleaning. Any suggestions for restoring all controls? They all worked fine before taking the blower motor out. This is on a 2001 2500 where the motor is located beneath the glove box.

You may also have knocked off a vacuum hose that controls the HVAC.
(That's the first I'd check, the system goes to defrost if it has no vacuum)

heater blower motor
 

I took the blower motor back out to check to see if I had not gotten the seal in right. After reading several posts about vacuum, I decided to drive the truck to see if the cruise was working. As soon as I started it up, the blower diverted from defrost to dash vents. Duh. I had only turned the key on before; not started the truck. Evidently you have to have start the truck for the diverter door to work? Does starting reset something? BTW , the cruise was working.

You need the engine running for the vacuum pump to work.
(The vacuum pump is on the left side of the engine, and it also drives the power steering pump - all driven by a gear from the crankshaft )

I'm not sure if this applies to the '98.5-'02 models, but on earlier years your ABS and brake warning lights will come on if you have a significant enough vacuum issue and change the diverter setting. Also if you activate cruise control, which is also vacuum driven.

The earlier years where the ABS and Brake warning comes on are before the hydroboost models.

(And I know some 97s with hydroboost, don't know when they started that)

But with enough of a vacuum issue you still have the trusty indicators of:
Defrost only
No 4WD
No cruise control
Even bigger oil spot on the parking lot. (The vacuum pump has it's "exhaust" into the crank case)
More fumes and smell from the crankcase vent.