PWM operation of the blower motor (Page 1/1)
imacflier MAY 18, 01:20 PM
Hi, All,

Since PWM motor controllers are readily available on Ebay in a wide variety of power handling abilities, it might make sense to do away with that damned fire hazard of a resistor pack and convert to Pulse Wave Modulation(PWM) of the blower motor. Among other advantages, a continuously variable blower speed could be readily implemented.

To do such a conversion, I need to know the maximum draw of the blower motor and I seem too dumb to find it in the FSM.

Could some kind soul just tell me what the maximum draw is? Please??

TIA,

Larry
theogre MAY 18, 04:50 PM
High speed blower runs direct "12v" via a relay from Fusible link A.
ONLY Low speeds use the resistor pack.
You have to rewire the car and maybe the PWM "box" to make it work.

Blower low speeds has 20a or 25a fuse so should have 25a PWM control minimum. (20a heat only, 25a heat/ac.)
PWM handles 25a or more likely will need air to cool a heatsink. Little or No air = short life to your "upgrade."
Other cars have Mosfets or Transistors that are in Heater/AC box for same reason as resistor pack.
Blower may only use 10a but having PWM w/ higher amp rating means MOSFET should run cooler.

Plus OE Switch is on thin wire that eats power to the motor vs purple wire to run high speed.
Get FSM etc and See my Cave, Wire Reading

Resistor pack sets lowest speeds so AC won't freeze up blocking air flow at minimum. That might even cause AC system problems killing the compressor etc.
Blower w/o enough power will burn out too. Example: You turn down PWM speed after running higher speed may run "ok" but forget then start the car hours to weeks at lower speed won't start the blower is where you fry it.
IOW "continuously variable blower speed" 0 - 100% isn't a great thing for many motors and why likely have to rewire the PWM "box." (Is not like a train set etc where is easy to see a motor not turning.)

Some could likely PWM the blower but is not a simple PnP w/ any "standard" module.
Quick example: A small Arduino could PWM the low speeds using same OE switch etc. Can mount the MOSFET in the ac/heat box likely using same wires and board.
While not continuously, That allow you to adjust each low speeds of a given setting of the OE control switch. When on high runs blower on OE relay.

Blower likely need a "flyback" diode or whatever to protect the MOSFET.

Later Resistor packs have screens and thermal fuses to prevent fires. Google them and use image pages to see many types.
Is mainly a fire problem now for most people because has decades to suck in leaves etc. Or stored for months for mice to live there.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

imacflier MAY 18, 05:57 PM
Thanks, theogre,

I think you have given me all the info I really need.

I will report back as this lil experiment proceeds.

Larry
pmbrunelle MAY 18, 06:45 PM
This project is also on my to-do list!
darbysan MAY 19, 11:08 AM
Just for info, I installed an Electronic HVAC control from a 96 Roadmaster in my El Camino. It has a PWM controller with a large heat sink that is normally mounted with the heat sink in the airflow of the fan, just like the resistor pack for cooling. I mounted it in front of the AC condensor, where it will get airflow from the truck moving or from the fan. So far, it's worked out OK in that location ( 8 yrs+), so that may be an alternative for you.

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'87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)