Front HVAC Blower - Need More CFMs!

[The_Full_Monte]

Hi, guys! More HVAC stuff here. So, I guess I should start with everything I've replaced in the past 2-3 years:
- Condenser
- Front and rear compressors
- Front and rear heater cores
- AC lines
- Heater core lines
- HVAC control module (dashboard control panel)
- Blower motor resistor (front)
- Blower and blower motor (front)
- Thoroughly cleaned and inspected front and rear evaporator coils and condensate drain lines

OK, so we got all that out of the way. Now, what I'm trying to do is get more CFMs from my front blower - the rear HVAC CFM is great. In my opinion, the front HVAC blower only seems to be blowing at partial capacity (not blowing at full speed, even on "high" setting). I know the grounding wire can be an issue. This was also addressed, and the grounding wire is solidly grounded. Is there a way I can do some custom electrical engineering to increase amps to the front blower motor, in turn, increasing blower speed and CFM?

 

[Schurkey]

Verify that the blower motor is getting proper voltage. Would be useful to use a low-ampere "amp clamp" and a 'scope to determine ampere draw of each armature bar, and calculate blower motor RPM so it can be compared to a "known-good" similar vehicle.

The only way to push more amperage through the blower motor is to increase the voltage. If you have excess resistance anywhere in the blower motor circuit, that will reduce voltage and therefore blower speed.

 

[Donald Mitchell]

Or some of the foam is gone missing from between the heater and dash/defrost vents. Just blowing behind the dash.

 

[GoToGuy]

Do you have any conditioned air leaking from the the ducts? Have you dropped the fan and cleaned ( vacuumed or blown out any debris inside. Clean the exchangers, fuzz or junk stuck in fins reduce airflow. Mode blend doors clean fully functional.
Electric blower motor draws current, amps it's designed for.
At speed it draws 10 amps at *** rpm. Through switching reducing, volts or amps, you have your 1/4, 1/2 , or high, medium, low speeds.
So simple changes, new squirrel cage deeper or larger, blades move more volume. A replacement blower motor with higher operating speed, higher velocity, ( same volume moving faster) . Although I'm pretty sure higher speed air would probably have higher air noise.
Myself I would opt for more volume than higher speed. The idea of " pushing more amps " means your not quite understanding DC voltage. Wire gauge has current limits.
Do you know " Ohms Law" ? Good luck.

 

[1998_K1500_Sub]

Is there a way I can do some custom electrical engineering to increase amps to the front blower motor, in turn, increasing blower speed and CFM?

You might look to the remote control racers’ bag of tricks, e.g., the Traxxas type of hobby cars, where it’s not uncommon to alter the windings on the electric motors to gain performance. I can’t say I’ve ever heard of anyone doing so to a blower motor, but why not? It’s just another permanent magnet DC motor.

Upgraded wiring to supply the motor is likely your easier initial approach. Measure the voltage across the blower motor now (blower on high, engine idling) and compare it to the alternator’s voltage (measure voltage at ALT output terminal to case, engine idling). Less than 0.5V difference between the two (blower vs. ALT) would be good, 0.2V would be better, 0.0V unattainable. Add wire and a relay(s) to achieve the objective.

The steps above will improve the “max” blower performance. Improving performance on lower settings requires additional changes. Ask if you’re interested.

As others have said, the air box’s parasitic air losses / leakage, and resistance to flow, are worthy of study and improvement.

On that note, a story: I once had a leaky evaporator. It was a slow leak, and the evaporator difficult to replace, so I lived with it. The oil would cause dirt to plug the evaporator core, so every couple of years I needed to thoroughly clean the evaporator to restore airflow.

 

[The_Full_Monte]

Although I'm not looking forward to this full day project, I think this is what needs to be done...because I've done everything else!

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[caw_86]

ive done some napkin engineering math, if you can take the squirrel cage blower off of the shaft and machine the shaft down from 5/16, down to a 1/4", and manage to reattach it balanced and centered, theoretically you should get about 20%ish more CFM. but i dont know the ratings of the motor and i cant find them anywhere, so i dont know what kind of extra current draw this will make

 

[1998_K1500_Sub]

ive done some napkin engineering math, if you can take the squirrel cage blower off of the shaft and machine the shaft down from 5/16, down to a 1/4", and manage to reattach it balanced and centered, theoretically you should get about 20%ish more CFM. but i dont know the ratings of the motor and i cant find them anywhere, so i dont know what kind of extra current draw this will make

For that type of motor (permanent magnet DC), the current draw is linear with delivered torque, being a minimum at no load (which you could measure with the blower removed) and maximum at stall (which is limited by the motor's DC resistance).

Torque is also linear, decreasing with increasing RPM, i.e., maximum at stall, minimum at no load - max RPM.

A graph, borrowed from a nameless source on the Internet, is below:

You must be registered for see images attach

The graph illustrates how the motor's torque increases linearly with decreasing speed. That's almost intuitive once you see it written down.

So:

You can measure the current draw presently, with the motor in the housing, using a DVM or DC current clamp. While you don't know, now, the torque delivered by the motor, you'll know the current, which is related to the torque. Read on...

You've estimated the change in airflow your changes will yield. You posted that, prior.

You can estimate how much, percentage-wise, the torque on the blower fan will increase with the increasing airflow (you decide on how you want to model that change as a function of airflow, e.g., linear, second-order, exponential...).

Finally, multiply the existing current draw by the percentage change in torque to yield an estimate of the resulting current draw after your changes.

 

[caw_86]

For that type of motor (permanent magnet DC), the current draw is linear with delivered torque, being a minimum at no load (which you could measure with the blower removed) and maximum at stall (which is limited by the motor's DC resistance).

It's also linear, decreasing with increasing RPM... maximum at stall, minimum at no load.

A graph, borrowed from a nameless source on the Internet, is below:

You must be registered for see images attach

The graph illustrates how the motor's torque increases linearly with decreasing speed. That's almost intuitive once you see it written down.

So:

You can measure the current draw presently, with the motor in the housing, using a DVM or DC current clamp. While you don't know, now, the torque delivered by the motor, you'll know the current, which is related to the torque. Read on...

You've estimated the change in airflow your changes will yield. You posted that, prior.

You can estimate how much, percentage-wise, the torque on the blower fan will increase with the increasing airflow (you decide on how you want to model that change as a function of airflow, e.g., linear, square-law, exponential...).

Finally, multiply the existing current draw by the percentage change in torque to yield an estimate of the resulting current draw after your changes.

A bit confused, the graph shows torque going down as rotation speed goes up, but then you mention the increase in torque.

 

[1998_K1500_Sub]

A bit confused, the graph shows torque going down as rotation speed goes up, but then you mention the increase in torque.

I mention two effects:

- torque linearly increases with increasing current
- torque linearly increases with decreasing speed


I may have caused confusion by inserting that graph of torque vs. speed, but I think of them as practically the same because of their relationship for this type of motor.