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 8:03 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 5:55 PM
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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 6:06 PM
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STRAILER
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Yep yep, let me know what happens
Jun 1, 2026 at 6:23 PM
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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 11:35 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 2:29 PM
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DAVENOOB
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Only one picture. Are both relays in same spot?
Jun 2, 2026 at 3:15 PM
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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 3:25 PM
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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 6:54 PM
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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 26, 2026 at 12:49 AM
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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 2:10 PM
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STRAILER
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Yes, that is correct.
Jul 26, 2026 at 3:00 PM
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DAVENOOB
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Thanks will let you know what happens.
Jul 26, 2026 at 4:02 PM
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STRAILER
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Sounds good
Jul 26, 2026 at 5:49 PM
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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 8:06 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 4:16 PM
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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 4:59 PM
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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 5:33 PM
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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 6:34 PM
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STRAILER
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Both can be connected or not.
Jul 28, 2026 at 12:39 AM
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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 6:01 PM
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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 3:08 PM
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DAVENOOB
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I did already 6.85 volts
Jul 30, 2026 at 4:26 PM
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DAVENOOB
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Exactly half of the 12.7 volts you said should be.
Jul 30, 2026 at 4:26 PM
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DAVENOOB
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The voltage at the fan was 0.
Jul 30, 2026 at 4:50 PM
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DAVENOOB
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The resistor harness was 6.85
Jul 30, 2026 at 4:51 PM
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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 7:16 PM
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