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AC Fan not working Part 2


SuiteSuccess
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I previously posted about my AC fan not working after coming home from a trip and turning off the truck then restarting after a brief period to reposition.  I originally thought it was a blown fuse but now discovered that fuse was on a different circuit and unrelated to the AC (ignorance and eyes getting old).  Anyway go over to work on truck, tear out half of dash, start up truck and fan blowing fine.  Turn off truck, restart in short order fan doesn’t work.  Shut off, wait ten minutes, restart and fan comes on.  So start listening closely and notice when I first start truck, turn the key to position one and normally hear 6 clicks.  When I shut it off, wait only about 15-30 secs only hear 3-4 and fan would not come on but truck starts.  This leads me to believe either a relay is sticking or is bad.  Haven’t tried changing the relay.  I will also confess my ignorance after 13 years driving this truck.  In picture 1 below of dials is where I normally positioned the fan switch after a trip, but in listening with just position one of the key before engaging the starter, I could hear the fan running after waiting several minutes after shut down.  In picture 2, I did not know the controls turned straight down and this was the real “fan off” position.  Turning the fan to that position seemed to allow a relay reset even after a short shutdown and the fan would come on.  I am also including the schematic for the AC fan if it helps anyone (thanks hatrack).  Any thoughts or ideas?  Am I on the right diagnostic track?TaMNV7Dl.jpg

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1 hour ago, SuiteSuccess said:

Okay got blower and resistor out. Having a hard time finding replacements for both. Anyone help?  Here are pics of the numbers. Fasco 2809-841-034M  E5762.  Resistor Behr 908.0016.12   (A3155 in black area)q8jO4whl.jpg

I grabbed a non OEM fan off Amazon and wired a physical switch in place of the resistor.

Good enough for a road repair,  provides high and off for now.

If I can find a proper resistor then great!  If not, I may just wire in a big PWM controller and call it done.

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Ok think my resistor (the U shaped thing) may be bad but want to make sure I’m checking it correctly. If you look at the picture there are four pins. If using a multimeter on the ohms setting and using pin 1 (furthest left) as ground and touching 2, 3, then 4 with red probe shouldn’t I show some ohm readings across each pin?  I’m showing nothing. I even repeated the process using each pin as ground. 

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2 hours ago, SuiteSuccess said:

Ok think my resistor (the U shaped thing) may be bad but want to make sure I’m checking it correctly. If you look at the picture there are four pins. If using a multimeter on the ohms setting and using pin 1 (furthest left) as ground and touching 2, 3, then 4 with red probe shouldn’t I show some ohm readings across each pin?  I’m showing nothing. I even repeated the process using each pin as ground. 

Not sure this will help :

https://i.ebayimg.com/images/g/JvUAAOSwbG5gPoZ9/s-l500.jpg

Edited by Pat & Pete
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On your picture above, I see one connector.  Is there one I can't see?  

Your testing is sound if this is a purely resistive component.  On the Gen 1, the resistor is simply a set of very large wire wound resistors.  Those resistors have to dissipate a whole lot of heat.  Therefore, I find it difficult to see that the relatively small "resistor" package will be able to do that.  The heat sinks on the back lean me towards something else is goin go.  I am thinking there may be active components something like some high power Zenner diodes that control the voltage to the fan.

Put the meter in the Ohms scale that has a diode next to it.  Touch the leads together to show that you have near zero ohms.  Do your test again and then reverse the meter leads and try again.   

Testing the motor should be straight forward.  Put 12 volts on the orange lead and ground on the black.  Should rotate in the direction of the arrow.  You can hold the motor.  Just tap on of the wires to see rotation.  Otherwise clamp it in something to hold it.  Those squirrel cage fans will present a lot of torque.

 

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Ok retested resistor with different settings. Will post results along with pertinent data. Unfortunately don’t know what the normal specs should be for the resistor but would save me $100 if I don’t have to replace it also. Using pin 3 as the ground according to Pete’s picture below I was only getting the following readings on 2000k ohms.  No readings on 200, 2000, 20k, or 200k.  The readings are as follows  Pin 1/3–nothing, pin 2/3-058 ohms, pin 3/4-338 ohms  No readings using pin 1,2,or 4 as ground,  Anyone able to interpret this?  Above my knowledge and pay grade.  Gonna replace fan motor regardless.  YTwJtuBl.jpg1XLeX5zl.jpg

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4 hours ago, SuiteSuccess said:

Ok retested resistor with different settings. Will post results along with pertinent data. Unfortunately don’t know what the normal specs should be for the resistor but would save me $100 if I don’t have to replace it also. Using pin 3 as the ground according to Pete’s picture below I was only getting the following readings on 2000k ohms.  No readings on 200, 2000, 20k, or 200k.  The readings are as follows  Pin 1/3–nothing, pin 2/3-058 ohms, pin 3/4-338 ohms  No readings using pin 1,2,or 4 as ground,  Anyone able to interpret this?  Above my knowledge and pay grade.  Gonna replace fan motor regardless.  YTwJtuBl.jpg1XLeX5zl.jpg

Carl,

I may be wrong but I believe pin 1 is 12vdc from battery, pin 2 is signal to trigger (probably scr pack) to determine the called for setting, pin 3 ground, pin 4 power out to motor. pin 1 to 2 should be open (power - ground) pin 2 to 3 would be across the signaling leg, pin 3 to 4 you are reading across the output to the motor, which would probably change based on signal on pin 2. Don't know what the reading should without knowing what is inside case.

Ken....

 

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I gotta say, that it's looking like a switching device, rather than a resistor. Quick and dirty check? Use an old analog meter on the motor leads, and adjust the knob. Meter set to DC volts, of course. That drawing posted by Pat, and your pics, show simple "magic" boxes, not resistor symbols.

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Thanks Ken & Darryl.  Fortunately I have an analog meter and will try as suggested.  Darryl, every video I’ve watched refers to that part as a resistor. Interesting the schematic does not.  Good pickup.  Guess I’m going to just have to break down and take it to shop but not before “playing” a bit more with the above suggestions.  I’m learning along the way.

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For $100 it would be far less expensive just to replace it.  If I pop a code on a vehicle, I will not take it to the dealer.  They just swap parts.  If the particular part did not fix it, they won't take it off and put the old back on.  They charge you for all the parts whether or not you need them.  I can do that myself.  

New Navy technical solution:  Swap till you drop.  Had to borrow that from the Air Force.  Army still sends it back to the Depot and gets a new one.  Marines ask the Navy to fix it. ☺️

Now, about that "resistor".  If you look at the side of it are there not two diode symbols on it?  Now, let's count connector pins.  One is ground, One is 12VDC straight off the 30 amp fuse.  That leaves two pins.  One must go to the motor drive and one must go to motor ground.  How could you get speed control within the "resistor".  IMO, Speed control must be coming from the large Climate Control Unit to the left by dropping the voltage on the motor drive. Note that the schematic shows 5 wires going to the Blower Control.  Perhaps the ground or power to the motor are shared.  That would leave 2 pins for control.  Perhaps then a binary signal from Climate Control Unit sends signals such as"

00 off

01 low speed

10 medium speed

11 High speed

I really wish I was in TN!  This problem sounds like a hoot and a good learning experience.  

And still, you need to test the fan motor.  You stated you were going to replace it anyway.  But you need to know if it was the problem. 

1.  If it does not work then replacing it only would be a good option.

2. If it does work then you can believe it is a problem before the fan.  Replacing the fan on GPs and the resistor would be a good option.

 Carl, can you send pictures of the wiring harness to the resistor and motor?  That would help.

 

Edited by NeverEasy
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Chet,

I checked the motor and it ran fine. I connected to 12 volt multiple times and it ran perfectly normal every time. So I got bold went over to truck reconnected everything back up including resistor (or whatever it is) after cleaning the pins and connectors. Made sure all wires were seated. Started truck up and it worked normally with fan going from low to medium to high multiple times also. Repeated several times by turning truck off then restarting and everything works as it should. Buttoned it up, replaced dash and trim and will keep my fingers crossed I released the gremlins without spending several hundred $$.  Thanks so much for the help. 🤞🤞

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Damn, I wanted the resistor!  Happy to hear it worked.  I would not be surprised if it quits again.  Handling the motors sometimes jolts the brushes and they make contact until they wear down again.  On the positive side, the resistor is not likely to fail and then come alive again.  And it could have been just bad connector contacts.  Use some DeOxIt.

https://www.amazon.com/CAIG-LABORATORIES-D100L-25C-Contact-Cleaner/dp/B0000YH6F8/ref=sr_1_4?crid=1JNJMWSHW16H5&keywords=cramoline+electrical+contact+enhancer&qid=1655343304&sprefix=cramoline+electrical+contact+enhancer%2Caps%2C50&sr=8-4

 

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10 hours ago, NeverEasy said:

Damn, I wanted the resistor!  Happy to hear it worked.  I would not be surprised if it quits again.  Handling the motors sometimes jolts the brushes and they make contact until they wear down again.  On the positive side, the resistor is not likely to fail and then come alive again.  And it could have been just bad connector contacts.  Use some DeOxIt.

https://www.amazon.com/CAIG-LABORATORIES-D100L-25C-Contact-Cleaner/dp/B0000YH6F8/ref=sr_1_4?crid=1JNJMWSHW16H5&keywords=cramoline+electrical+contact+enhancer&qid=1655343304&sprefix=cramoline+electrical+contact+enhancer%2Caps%2C50&sr=8-4

 

If it acts up again, I’ll send it to you.

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22 hours ago, NeverEasy said:

Now, about that "resistor".  If you look at the side of it are there not two diode symbols on it?  Now, let's count connector pins.  One is ground, One is 12VDC straight off the 30 amp fuse.  That leaves two pins.  One must go to the motor drive and one must go to motor ground.  How could you get speed control within the "resistor".  IMO, Speed control must be coming from the large Climate Control Unit to the left by dropping the voltage on the motor drive. Note that the schematic shows 5 wires going to the Blower Control.  Perhaps the ground or power to the motor are shared.  That would leave 2 pins for control.  Perhaps then a binary signal from Climate Control Unit sends signals such as"

00 off

01 low speed

10 medium speed

11 High speed

 

 

The common practice in automotive electronic controls today, especially of things like motors, etc., is in fact digital, as you suspect, but not exactly as you imagine it to be.  They typically use pulse width modulation (PWM), where low speed would be achieved by the control module sending a series of brief intermittent pulses of electricity to the motor, resulting in low speed operation.  Medium would use slightly longer pulses, and high would pulse so frequently that the delivery of power would be nearly continuous, with the motor speed varying with the length of the pulses. 

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Thanks, Phil D.  I should have thought of that.  I use PWM to control the speed and output of a cat feeder I designed with an Arduino chip.  Sure would like to have put a o-scope on Carl's truck.  Could have gained useful info to pass on.

Cheers!  Chet

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