When I'm driving '72 Chevelle with the A/C and the headlights on everything is good, however when I come to a stop the A/C fan slows down and the lights get dim. I have since converted to a 105 amp alt from a '88 Firenza (part# 1346-5-11). Now everything works great. Lights stay bright and the A/C fan don't slow down anymore. It is great and it was very easy to make the conversion. Here is my problem, When I have the A/C fan on high it feels like the same speed as a modern day car's A/C fan when on medium. Is there a way to add a relay or something to speed up the fan to get more air flow in the car?
Thank you,
plutopjf

Our older cars don't blow as hard as the new ones. Would not want to over power the fan, may burn it up.

I would say, no. The windings are set in a certain way and are not as efficient as today's blowers. The only think you could do (DON'T) is to increase the voltage to the motor and that could be real bad.

Chuck

Sometimes a bunch of leaves and debris block the air flow through the evaporator coil.

is the high speed fan relay kicking the fan into "overdrive" like it's supposed to?
i know that on my 74 Monte, it has a relay that kicks it into a "higher" high speed when i put the selector to the "max" AC spot. my car has an inline fuse that provides full battery power directly from the alternator that blew out once, and i could not figure out why i didn't have as much airflow as it used to. put a new 30 amp fuse in it, and all was good.

Cheap replacement fans are weaker than good quality manufacturer fans. I have had good luck with Delco fans.

Cheap replacement fans are weaker than good quality manufacturer fans. I have had good luck with Delco fans.
Not saying that is untrue but I've never seen any difference myself.

If the motor is the same RPM as the original and the blade is the same as the original, it has to move as much air as the original.

I can't see how they could make a motor cheaper by changing either the RPM or the blade.

I worked for a car company (not GM) on AC systems in the early 70's and there is a performance difference between AC blower motors and heater-only motors. The AC motors had permanent magnets while the heater-only motors had wound field coils. I am not sure if Delco did this, but I suspect that they did. Make sure you have the proper motor.

Can I change it to a more modern fan? Maybe from a 2000+ model car? Do you think that would work?

Delco fans of that era used permanent magnets for the magnetic field. The motors were very simple. They will slow down over the years due to increasing friction in the rotor shaft bearings and also by rising resistance in the brush contacts to the commutator. That is, at the sliding connections that provide current to the rotor windings.
Blower motor speed was controlled simply by selecting different resistors via the speed selector switch. For max speed, the high speed relay gets energized and, I believe, supplies full battery voltage to the motor. Did your car have factory A/C? Stonger motors were used on A/C vehicles to move the denser cold air.
Many modern blower motors are electronically controlled without need for resistors or the brushes.

The key is in the blower wheel, the larger the diameter and the longer width, also the larger the fins, the more air it will move.

Most all older GM blower motors are the same RPM speed @ same voltage.

Have an electric motor shop rewind it.:yes:

Check for debris in the evap, the old motor might just be tired, I have had good luck and better volume with just a motor change.

Pick up a parts store made in china replacement and compare the weight of the original. The lighter one makes less torque and moves less air. Try to find a local electric motor shop and have the original motor rebuilt.

Any motor manufactured anywhere turning the same blower wheel at the same RPM will move the exact same amount of air. :yes: