The air movement that creates the negative pressure (vacuum) is being redirected to the intake manifold to serve engine acceleration - making the vacuum drop.
Because you have a vacuum leak in the system or your vacuum canister is leaking. When you accelerate the vacuum from the engine will drop. That will cause your system to loose vacuum and the floor/defrost door will go to its neutral position. To keep the vacuum up you have a canister that will hold vacuum. It must be air tight.
You either have a bad, cracked or loose vacuum line or you have a broken a/c - heater control door that closes when you are accelerating......
You have a bad vacuum reservoir or leaking vacuum line. Vacuum is usedd to control the air duct doors in your system and when you accelerate, the vacuum supply is greatly reduced...causing the duct doors to "default" to the defrost position.
accelerate
because the voltage drop.
The accent symbol of the word "accelerate" is on the second syllable: ac-CEL-er-ate.
This may be a vacuum problem not an electrical problem. Determine if you hear the fan running? When you accelerate the engine vacuum is reduced and the heater/ AC door diverts to floor instead of upper vents.
Low vacuum. When you push down on the accelerator, vacuum decreases. Your Blower doors use vacuum to change positions from floor to vent to defrost. Have a vacuum test done on the vehicle. You may have a vacuum leak, or this may be a sign the engine is getting weak.(Low compression, Leaking valves, etc.)
My truck flutter and temperture gauge drop at the same time
Assuming you mean "increases" in speed, as you accelerate the engine the HVAC (Heating Ventilation Air Conditioning) system is loosing its vacuum supply to function properly. Normally the system depends on a vacuum reservoir to maintain operation. This happens when the vacuum supply from the engine is leaking because of damaged/cracked/pinched vacuum lines. Inspect all the vacuum lines associated with the HVAC system.
The 1995 Monte Carlo could have a vacuum leak. An engine vacuum leak can make the car idle up and accelerate.
A Vacuum.