I have this 1993 Roadmaster with automatic climate control and the blower motor is full speed all the time even with key off, so I have to keep pulling the 30 amp fuse.
So the blower control module is continually passing power to the blower motor by way of a shorted semiconductor.
The module costs $96 so If I could repair it would help me a lot.

Has anyone ever worked on these modules?
The climate control module sends a variable voltage to the blower control module depending on desired blower speed and the blower control module adjusts the blower motor speed.

I never hear of anyone repairing this except by buying a new module. I have repaired several other modules on my Roadmaster, one for the automatic headlights, the other for the auto down driver window.

 

Its done with pwm to a Mosfet transistor, if you take pictures of the faulty item you might get better answers, you canmake your own motor speed controller,

Search 555 pwm motor speed

http://m.ebay.co.uk/itm/Brand-New-S...%3Adfd9a4ea1580a35713b180cafff4b407%7Ciid%3A6

 

Its done with pwm to a Mosfet transistor, if you take pictures of the faulty item you might get better answers, you canmake your own motor speed controller,

Search 555 pwm motor speed

http://m.ebay.co.uk/itm/Brand-New-Smallest-DC6-15V-4A-50W-PWM-DC-Motor-Speed-Control-for-775-555-motor-/291541610671?hash=item43e13bf0af:g:1icAAOSwjVVV0VWk&_trkparms=pageci%3A393d3070-bd7a-11e6-ac00-005056a07dc4%7Cparentrq%3Adfd9a4ea1580a35713b180cafff4b407%7Ciid%3A6

Thanks for that.
I will pull it off car in a few days and post some pics.

The blower motor pulls 15.5 amps on high speed.
If the blower motor drags or leaves stop up the air flow, the whole thing can overheat and or amps can go up I read, and higher amps and or moisture around this motor controller causes it to fail. One video showed a bad motor pulling 23 amps, and a new one 15.5 amps.

 

If you decide to by a pwm kit, you can always change the Mosfet transistor for a bigger current.

 

Does that controller have a conformal coating on it or can you get at the components fairly easily. I have a schematic for thst I think. There are a lot of places that fix HVAC controllers. Can you post really good pictures of the unit?

 

Well it is history, the way they make this is impossible to repair the existing parts. But might be able to use it as a form to make your own circuit.
Any ideas?

 

To get the heat sink plate removed, I used a propane torch.
They were all SMD and had a jelly like substance all over the inside.
The heat sink was glued with black epoxy on the edges and at the front where are the electrical connections.

 

Does that controller have a conformal coating on it or can you get at the components fairly easily. I have a schematic for thst I think. There are a lot of places that fix HVAC controllers. Can you post really good pictures of the unit?

Can you post a schematic circuit diagram?

 

http://www.ebay.com/itm/10-50V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V-50V-2000W-MAX/311469198861?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=38530&meid=6fac7d974b9c450ea15eee261d619454&pid=100005&rk=3&rkt=6&sd=111851538617

You can buy a 40 amp motor controller for cheap.
But how would you integrate into the existing climate control module which uses a paddle switch to adjust the blower speed versus this item which uses a variable resistor? ASFAIK, the paddle switch varies a voltage signal to the blower motor control .

I suppose a working circuit should take a variable voltage input and supply a much larger current with a variable voltage output linked together stepwise...depending on user input pushing the paddle switch back and forth. That part is already done as a feature of the climate control module, so a working circuit would mirror the other circuits voltage as the paddle switch is pushed but have available a much higher amperage to run the DC blower motor.

Here a person shows with a meter how the voltage changes coming from the climate control module from like 1.6vdc to 12 vdc. etc...

 

That's too bad. I fixed one on a Chrysler minivan once, by replacing a single MOSFET that had failed to a short as I recall, meaning the fan was on full blast all the time. I had to replace the next one that failed (different vehicle). Not sure why. But the price has come down over the years. Used to be $85 from the dealer and now I can get one for $20 or so. Shop around.

 

That's too bad. I fixed one on a Chrysler minivan once, by replacing a single MOSFET that had failed to a short as I recall, meaning the fan was on full blast all the time. I had to replace the next one that failed (different vehicle). Not sure why. But the price has come down over the years. Used to be $85 from the dealer and now I can get one for $20 or so. Shop around.

The new ones are a better design and can be repaired, I bought one for another Roadmaster Wagon a few years ago.
Cheapest I have seen is $91 on ebay.

 

The new ones are a better design and can be repaired, I bought one for another Roadmaster Wagon a few years ago.
Cheapest I have seen is $91 on ebay.

RockAuto.com has them for $20 if you need the type for a heater that just has a knob speed control and the red/blue knob for temp control. It you have a thermostat (dial-a-temp) type, the GM OEM is the only option for about $90.

I'm guessing there is a Microcontroller in it so be careful if you try to open it.

 

I have read about PWM circuits driving DC motors.
They turn the motor off and on at full voltage to turn the shaft at various RPM.
Probably using a timer like 555 chip and a mosfet to drive the DC motor.
I can wait on buying the module, so if someone has a schematic that would work using the input from the climate control module...versus a potentiometer. See you want the Automatic climate control feature to control the blower, otherwise it is no longer automatic.

So far every circuit I see shows a pot to adjust the speed.
How would you change the circuit to use a varying DC voltage to adjust the speed instead of a pot?

 

http://www.theorycircuit.com/dc-motor-speed-control-using-ic-555/

For example here

Could the varying voltage coming from the Climate control signal wire be attached to one of the 555 pins? Probably not.

 

http://www.pcbheaven.com/circuitpages/Voltage_Controlled_PWM_Generator/
Finally found a voltage controlled PWM generator that does not use a microcontroller.

Am I on the right track?
Except that this seems to be inverted, higher input volts, lower duty cycle.

 

Hello,

Have a look at post #4 of this thread:
http://forum.allaboutcircuits.com/threads/more-555-pwm-questions.49060/

The control voltage is here done by the potentiometer, but should be between 1/3 Vcc and 2/3 Vcc.
Also the power stage is missing, but a mosfet will cover this.

Bertus

 

See you want the Automatic climate control feature to control the blower, otherwise it is no longer automatic.

So far every circuit I see shows a pot to adjust the speed.

I think you'll have a hard time retaining original ATC with a DIY solution. In my Chrysler, I think some of the smarts of the ATC are contained in the fan control module itself. It's not nearly so simple as receiving an analog voltage or such on a wire and converting it to PWM for the fan.

If you can find reference information that proves this wrong, that there is a signal you could use to control a PWM circuit, then never mind what I just said.

 

I think you'll have a hard time retaining original ATC with a DIY solution. In my Chrysler, I think some of the smarts of the ATC are contained in the fan control module itself. It's not nearly so simple as receiving an analog voltage or such on a wire and converting it to PWM for the fan.

If you can find reference information that proves this wrong, that there is a signal you could use to control a PWM circuit, then never mind what I just said.

Its a GM. The signal voltage varies up and down as you press the paddle switch up and down. So it seems simple.

 

Hello,

Have a look at post #4 of this thread:
http://forum.allaboutcircuits.com/threads/more-555-pwm-questions.49060/

The control voltage is here done by the potentiometer, but should be between 1/3 Vcc and 2/3 Vcc.
Also the power stage is missing, but a mosfet will cover this.

Bertus

Thanks, seems like it could work. She said it could be configured with a variable input voltage, how would that be done? Simple attach the variable + DC outptut from the climate control module to the + on the LM339?

I can get some more accurate DC volt data from that signal wire for various blower speed settings.

Ok, linking to an LM339 for info purposes.
http://www.engineersgarage.com/electronic-components/lm339-datasheet

 

Hello,

As I said, you can use a control voltage on the +input of the comparator in stead of the drawn potentiometer.
The voltage should be between 1/3 Vcc and 2/3 Vcc.
You will have to adapt the voltage from the controller to this range.
(there might be an offset and gain needed).

Bertus