Heat/cool fan won't turn on?

2017 DODGE RAM
120,000 MILES • TURBO • 4WD • AUTOMATIC • DIESEL
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DAVENOOB
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My fan stopped working and I replaced a few parts. The console with the knobs, regulator, and fuse. I hooked 12v to fan and it works. Also the console with knobs isn't lighting up. I'm helping a friend who isn't internet literate so kinda going off what he has told me. Tomorrow we are going to run voltage meter and see if we can find where the power stops. I'm unfamiliar with this car. Besides running voltage meter and following power what else should I be aware of? I realize the regulator and front control console panel probably aren't the problem if properly installed. Big if anyways any heads up pointers would be great. From there I'll run tests and update/ask as needed. Thanks

2017 dodge ram diesel 2500 6.7
May 31, 2026 at 1:03 PM
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STRAILER
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So first I would check the power and ground to the blower motor this guide will show you how.

https://www.2carpros.com/articles/how-to-test-an-automotive-hvac-system-blower-fan-motor-a-detailed/

Most of the time the problem is the blower module or did you replace that and you called it a regulator? Also, there is a blower motor and a run 1 relay in the fuse panel under the hood. While you are there check the #84 fuse 15 amp. Here is the wiring diagram so you can see how the system works. Check out the images (below). Please let me know what happens.
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Jun 1, 2026 at 10:55 AM
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DAVENOOB
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He called the regulator the part that regulates the power for fan settings. Low 4volts, medium 6 volts and so on. Like I said once I get into the car I can give more info. Thanks for the start.
Jun 1, 2026 at 11:06 AM
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STRAILER
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Yep yep, let me know what happens
Jun 1, 2026 at 11:23 AM
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DAVENOOB
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Ok that diagram is past my knowledge level. Where's the run 1 relay located? I'll let you know.
Jun 1, 2026 at 4:35 PM
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STRAILER
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No worries, here is the location of both relays. Check out the images (below). Please let me know what happens.
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Jun 2, 2026 at 7:29 AM
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DAVENOOB
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Only one picture. Are both relays in same spot?
Jun 2, 2026 at 8:15 AM
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STRAILER
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They might be internal to the PDC. I would check for power to the dr/blu wire at the fan motor when the AC is on and running first. This guide can help

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester/

Please go over this guide and get back to me.
Jun 2, 2026 at 8:25 AM
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DAVENOOB
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Alright so did all sorts of tests. Fan works when relay is bridged, power seems to end in the resistor which has been replaced. I checked the relays(new and old) and was at .5. The one test I forget what it was but only pulled 8 ohm or volts when should 12.6 ohms/volts or there is a power overload issue I belive it said. Sorry I can't be more specific but was testing old and replacement parts for the whole thing so sone of the tests run together. Let me know if this makes sense or if you can make sense of it. Thanks
Jul 25, 2026 at 11:54 AM
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STRAILER
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IT sounds like you have a bad ground can you please check the G910A which is the black wire at the blower motor module. Let me know.
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Jul 25, 2026 at 5:49 PM
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DAVENOOB
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No black wires just blue wires with colored stripes on them. What's the blower motor module? The resistor? So test the ground wire on the resistor?
Jul 26, 2026 at 7:10 AM
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STRAILER
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Yes, that is correct.
Jul 26, 2026 at 8:00 AM
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DAVENOOB
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Thanks will let you know what happens.
Jul 26, 2026 at 9:02 AM
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STRAILER
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Sounds good
Jul 26, 2026 at 10:49 AM
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DAVENOOB
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Ok so all the wires for harness going into control module are closed lines except the ground. The ac compressor engages when ac turned on. The wires in harness going to resistor(db/yel, db/blk, db red, db/pur) they were all close circuits except the ground. The harness to the fan has power as closed circuit but not the ground. The lines out of the control module are thin blue, blue/yellow, black, blue/pur,blue orange. I think I tested resistor correctly. Find ground wire and do continuity test for closed circuit and that was fine. Let me know if this makes sense.
Jul 26, 2026 at 1:06 PM
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STRAILER
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Yep, that is good the ground is working. Now, with the system on, check both dr/blu wires at the blower motor and the speed control for power (12 volts), and let me know.
Jul 27, 2026 at 9:16 AM
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DAVENOOB
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Car running or just accessory with fan turned on? So turn on and test 12v at resistor with resistor off, then same but with fan unplugged? Or the control module with knobs?
Jul 27, 2026 at 9:59 AM
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STRAILER
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Yes, the car must be on with the HVAC system turned on as well with the blower motor at any speed.
Jul 27, 2026 at 10:33 AM
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DAVENOOB
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Ok so test 12v at the resistor harness with the resistor unplugged then the fan motor harness with resistor connected and the fan not connected?
Jul 27, 2026 at 11:34 AM
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STRAILER
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Both can be connected or not.
Jul 27, 2026 at 5:39 PM
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DAVENOOB
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Voltage from control unit to resistor was 6.85 no matter the fan speed. 0 voltage to the fan. Also the control unit lights would go out over low speed. Both control units same results. Doing a system reset by unhooking batteries and turning the key to acc for 10 min.
Jul 29, 2026 at 11:01 AM
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STRAILER
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Can you give me the results of the 12 volt test to the wires in the post above?
Jul 30, 2026 at 8:08 AM
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DAVENOOB
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I did already 6.85 volts
Jul 30, 2026 at 9:26 AM
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DAVENOOB
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Exactly half of the 12.7 volts you said should be.
Jul 30, 2026 at 9:26 AM
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DAVENOOB
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The voltage at the fan was 0.
Jul 30, 2026 at 9:50 AM
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DAVENOOB
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The resistor harness was 6.85
Jul 30, 2026 at 9:51 AM
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DAVENOOB
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The hard reset by draining battery didn't help. Didn't think it would be couldn't hurt to try.
Jul 30, 2026 at 12:16 PM
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STRAILER
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Then you found the problem, the dr/blu wire should have 12 volts, it is supplied at the blower relay which is located at the fuse panel under the hood. I would swap the relay out and test again. Also, please test pin 30 for 12 volts at the relay.
Jul 31, 2026 at 8:35 AM
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DAVENOOB
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Checked 2 relays plus 2 from the truck already in use,same thing. So the old one, a new one, and 2 currently used and working from the fuse box. Checked the voltage with these relays. I'll check pin 30 and let you know.
Jul 31, 2026 at 12:12 PM
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STRAILER
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Okay sounds good.
Jul 31, 2026 at 7:00 PM
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DAVENOOB
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Engine off is 12.23v engine on 12.17v
Aug 1, 2026 at 11:20 AM
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DAVENOOB
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Is this part of this system? Passenger side side kick panel.
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Aug 1, 2026 at 11:22 AM
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STRAILER
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That look like it i a radio antenna. So the blower motor and speed control has power and ground correct? IF so lets check for power and ground at the HVAC controller. Here is where to check for power and ground.
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Aug 2, 2026 at 8:23 AM
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DAVENOOB
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Ok that makes 0 sense to me. Don't have any idea what I'm supposed to be looking at. What part located where?
Aug 2, 2026 at 8:37 AM
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DAVENOOB
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Ok so the console control. Are those different wiring harnesses?
Aug 2, 2026 at 8:40 AM
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DAVENOOB
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I'll Google it.
Aug 2, 2026 at 8:43 AM
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DAVENOOB
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Google is all over the place. Are you referring to the Heater control module behind the glove box or the part that is visible in the console to switch from heat to cool and fan speeds?
Aug 2, 2026 at 8:50 AM
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STRAILER
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The part that is visible that you turn the knobs at which is not lighting up.
Aug 2, 2026 at 9:04 AM
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DAVENOOB
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Ok power going to controller 12.43 volts. Power going out of controller couldn't get any voltage with and without the 5 wire harness plugged in. Also tried with old and new controller the voltage would hit .2-.3 but no real voltage. Stuck wires in back of harness while plugged in and tested and same results both controllers.
Aug 2, 2026 at 1:15 PM
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DAVENOOB
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The controller lights up until fan is turned above low speed power stops. Hazard lights work and knobs light up.
Aug 2, 2026 at 1:16 PM
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STRAILER
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It sounds like you have a and controller, plus please go over the testing again. Also go over all wiring, here is a guide use the diagram above.

https://2carpros.com/articles/how-to-check-wiring/
Aug 2, 2026 at 4:19 PM
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