Air Flow is very weak on my 1998 K2500

[Braydenw958]

I have a 1998 K2500 crew cab 4x4 LS swapped I’m having problems with the hvac system. It has very weak air flow I replaced blower motor and resistor and cleaned evap box as good as I could all actuators seem to function right. I can change from defrost, floor and main vents just doesn’t blow hard. Any help would be very much appreciated!

 

[L31MaxExpress]

It is too bad that someone has not come up with a brushless motor as a retrofit for the older GM blower motors. It would not be too hard to build a brushless blower motor with a control board that eliminated the blower resistor and high blower relay. Build it in a weather proof case that can mount underhood or under the dash. Provide a pigtail to connect in place of the resistor and relay. GM used the same blower motor for like 30 years and it is not an uncommon desire to have more airflow.

I was actually looking at the late 90s GM Cadillac brushless blower motor the other day. If I had enough knowledge to setup a PWM control circuit with a stepped input based on the speed setting I would attempt a conversion with one. The circuit board that controls it is built on to the blower, the blower has 3 wires. Power, Ground and PWM control input.

 

[L31MaxExpress]

If I could get my hands on an inexpensive C6/C7 blower motor I would like to mess around with it and see if it actually moves more airflow. The C7 blower looks like it would be easy to adapt to the Express van. Spins the same direction, has an identical looking flange, 3 wires using PWM input control. Looks like the wheel from the Express blower would interchange. I would use an inexpensive PWM signal generator for prototyping. I do not think it is something that could be used as a long term solution because the circuit board housing does not look to be sealed. It would be more of an experiment to see if the brushless motor actually improved airflow.

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[jd33173]

Are you sure that the door is closing all the way when you go into recirc mode on your ac?

 

[Schurkey]

Perhaps a moderator will move this thread out of ENGINES and into OEM + Custom Interiors.

The USUAL problem with poor air flow is not related to the blower motor unless the blower motor is defective.

The main issue is typically a debris-plugged evaporator core. Pine needles, leaves, cottonwood fluff, butterflies...anything that falls into the HVAC plenum can be pulled down into the blower motor fan area, and then plastered against the Evaporator.

NOT the worst I've seen...but the only one I have photos of.

You must be registered for see images attach

The second issue is a lack of voltage/amperage (power) to the motor due to high resistance in the circuit, or a failed blower motor. At minimum, a two-step voltage-drop test of the blower high-speed circuit is warranted. Test the + side of the circuit--battery + to motor +; and then the ground-side--battery - to the blower motor ground tab. You may have to extend the leads of your voltmeter using primary wire; the gauge size is fairly unimportant. Anything heavier than 16-gauge is plenty, 18 gauge may work too.

Ideally, you'd use a low-ampere current probe and an oscilloscope to check average amperage draw, and check each individual bar of the blower motor for current draw, looking for one or more bars that differ significantly from the others. And from there, you can calculate the motor RPM.

LASTLY, the quality of the motor itself is something to assess. I put in a "top quality" HVAC blower motor from NAPA into my '88 K1500. When it died some years later, I got an OEM motor from ACDelco. The Delco motor was obviously heavier/more powerful than the so-called "top quality" NAPA motor.

Other possibilities that are less common: Fan "squirrel cage" slipping on the motor shaft--fan turns slower than the motor. Debris inside of the fan, or in the plenum blocking air flow.

 

[L31MaxExpress]

Perhaps a moderator will move this thread out of ENGINES and into OEM + Custom Interiors.

The USUAL problem with poor air flow is not related to the blower motor unless the blower motor is defective.

The main issue is typically a debris-plugged evaporator core. Pine needles, leaves, cottonwood fluff, butterflies...anything that falls into the HVAC plenum can be pulled down into the blower motor fan area, and then plastered against the Evaporator.

NOT the worst I've seen...but the only one I have photos of.

You must be registered for see images attach

The second issue is a lack of voltage/amperage (power) to the motor due to high resistance in the circuit, or a failed blower motor. At minimum, a two-step voltage-drop test of the blower high-speed circuit is warranted. Test the + side of the circuit--battery + to motor +; and then the ground-side--battery - to the blower motor ground tab. You may have to extend the leads of your voltmeter using primary wire; the gauge size is fairly unimportant. Anything heavier than 16-gauge is plenty, 18 gauge may work too.

Ideally, you'd use a low-ampere current probe and an oscilloscope to check average amperage draw, and check each individual bar of the blower motor for current draw, looking for one or more bars that differ significantly from the others. And from there, you can calculate the motor RPM.

LASTLY, the quality of the motor itself is something to assess. I put in a "top quality" HVAC blower motor from NAPA into my '88 K1500. When it died some years later, I got an OEM motor from ACDelco. The Delco motor was obviously heavier/more powerful than the so-called "top quality" NAPA motor.

Other possibilities that are less common: Fan "squirrel cage" slipping on the motor shaft--fan turns slower than the motor. Debris inside of the fan, or in the plenum blocking air flow.

I did a substantial amount of testing recently using a new GM blower motor. I monitored both voltage and amperage to the motor as well as the airflow speed from the center vents. What I found is a sharp drop off in blower motor speed after the first ~5 minutes of operation. The voltage remains constant but the amperage drops as the blower motor heats up. The resistance of the blower motor is actually increasing when it is hot causing it to slow down. I noticed the condenser pusher fan does the same thing. Hence my interest in a brushless motor. I have very strong airflow for the first 2-3 minutes then it gradually falls off as the motor heats up and stabilizes at the newer output which results in a ~30% loss of air velocity at the vents.

I have tested two different Nissan vehicles with brushless blower motors that do not suffer the same rpm/airflow reduction. They deliver almost the same airflow after running full speed for 30+ minutes as they did cold.

Not saying in this instance the system does not have faults but in my case it is very much the 80+ year old blower motor design GM regurgitated for decades. It would be nice if an aftermarket manufacturer stepped up and offered a more modern replacement that actually works well. The life expectency of a brushless blower motor is around 30,000 hours. Many last the lifetime of the vehicle.

I have also considered trying out a Corvette brushless cooling fan on the 87 G20 van. It has some cool features and moves a ton of CFM.

 

[Braydenw958]

Are you sure that the door is closing all the way when you go into recirc mode on your ac?

I’ll definitely check and let you know

 

[Braydenw958]

Perhaps a moderator will move this thread out of ENGINES and into OEM + Custom Interiors.

The USUAL problem with poor air flow is not related to the blower motor unless the blower motor is defective.

The main issue is typically a debris-plugged evaporator core. Pine needles, leaves, cottonwood fluff, butterflies...anything that falls into the HVAC plenum can be pulled down into the blower motor fan area, and then plastered against the Evaporator.

NOT the worst I've seen...but the only one I have photos of.

You must be registered for see images attach

The second issue is a lack of voltage/amperage (power) to the motor due to high resistance in the circuit, or a failed blower motor. At minimum, a two-step voltage-drop test of the blower high-speed circuit is warranted. Test the + side of the circuit--battery + to motor +; and then the ground-side--battery - to the blower motor ground tab. You may have to extend the leads of your voltmeter using primary wire; the gauge size is fairly unimportant. Anything heavier than 16-gauge is plenty, 18 gauge may work too.

Ideally, you'd use a low-ampere current probe and an oscilloscope to check average amperage draw, and check each individual bar of the blower motor for current draw, looking for one or more bars that differ significantly from the others. And from there, you can calculate the motor RPM.

LASTLY, the quality of the motor itself is something to assess. I put in a "top quality" HVAC blower motor from NAPA into my '88 K1500. When it died some years later, I got an OEM motor from ACDelco. The Delco motor was obviously heavier/more powerful than the so-called "top quality" NAPA motor.

Other possibilities that are less common: Fan "squirrel cage" slipping on the motor shaft--fan turns slower than the motor. Debris inside of the fan, or in the plenum blocking air flow.

Thank you

 

[jd33173]

Thank you

Compared to the one i took out of my truck, that one looks choice! Also, If the door to the cowl doesnt close you dont get the strongest perceived air flow (for a given fan speed).

 

[Caman96]

I watched this video and actually did this when I bought my truck in 2020. Very easy to do if it needs cleaning, which mine didn’t, but it freshened up the air a bit.

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