Weird thing. When I have my air conditioning on, the fan slows down when I accelerate, then it speeds back up once I let off the gas. What the heck?

 

depending on how much you "accelerate" the pcm disengages the compressor based on tps.
which can make it feel off, well it is.

how much acceleration are we talking about here, do you just mean the blower?

 

At any speed when I roll into the throttle you can hear and feel the blower fan slow down and less cold air comes through the vents. When I let off the gas you can hear and feel the blower fan speed back up and cold air begins blowing normal again.

I don't think it does it if I very gently accelerate, but a moderate acceleration or more will do it, especially if I roll in hard enough to cause the A4 trans to downshift.

 

I would be curious to know if there is a significant voltage drop under acceleration (monitor DIC v/s analog). The PCM does not control the blower motor speed; however, it does shut down the compressor at a certain RPM, WOT, etc.

 

The car has 160K miles on it and has just gotten a new AC system and a blower, so that equipment should be OK. However, I might have a charging problem. I still have my original alternator and I am getting ready to replace it because I have noticed my voltmeter is sometimes dropping to about 11 volts at times. Also, I can see my voltmeter "bounce" when my turn signal is blinking. I will let you know if the new alternator fixes the AC Blower slowdown on acceleration, hopefully in about 3 weeks.

 

What year of car?

And as Lucky posted, watch the battery voltage when it does that.

 

I would take a close look at the connections and grounds before I bought a new alternator. Some year Vettes are very picky about after market alternators...may be better to have yours rebuilt if it is indeed bad.

 

I wonder if what your hearing just "sounds" like the blower slowing down but is in actuality the internal damper doors in the HVAC changing position(s), resulting in different internal airflow inside the HVAC housing that makes it "sound" like the blower is "slowing down" when you accelerate. When you accelerate hard, the manifold vacuum drops significantly until engine rpms stabilizes (steady throttle) or until you decelerate and your HVAC system relies on manifold vacuum to operate the internal damper doors.

Initially, you can check to see if the airflow pattern changes from say, the dash vent registers to the floor registers, or the defrost vent register up at the windshield when you accelerate hard for a few seconds. There should be no change in where the air comes out when you accelerate.

While doing your troubleshooting for the other things mentioned already, check to see if the small vacuum line at the rear of your intake manifold is broken/loose/disconnected OR is compromised somewhere else like under your battery (think possible battery acid leak resulting in damaged nylon vacuum line) OR if there has been any bodywork done and the vacuum connection(s) were not reinstalled properly under or near the battery. Check all the vacuum line connections going to the little vacuum reservoir tank (whose purpose in life is to prevent this) and closely examine the small vacuum check-valve too. If you've recently worked on, or removed, any of the interior components like your HVAC control panel, check the backside to be certain the vacuum line connector(s) is/are secure. There is a purple nylon vacuum that comes inside the passenger compartment through the firewall and must be intact.

HTH