I posed this question earlier and forgot to mention that the car is a Kia Spectra '07. Whenever you slow the car or idle, the speed of the heater fan slows considerably. When you accelerate, the fan speed picks up considerably. Is this normal? Know very little about cars and this has happened in the past when the alternator was going bad in another car. Someone please HELP!!
Have the charging system and battery checked to see if there is a problem with it or possibly in the wiring. Also make sure the fan belt for the alternator is tight. It may be slipping and not allowing the alternator to charge the battery as it should be. Since the car is pretty new this may be the case.
The blower motor speed varies with voltage changes to it. It sounds like the battery isn’t getting the full charge it normally should get so the voltage will go down more than it would normally while the engine idles.
I agree with cougar, the battery is low or the alternator is overcharging.