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willysmith 02-05-2012 09:16 PM

Heater/Air Con Fan died
First of all you guys are fantastic!! You solved a tail light issue for me earlier. THANKS. RAM1500 quad cab 2003 SLT 4.7 engine 4WD My heater fan worked fine in truck today and it never came on, no sound ,no fan! I checked the #4 fuse and it appears good. I just don't understand how it could die without any warning or noise? Any ideas? I wiggled the key switch alot too, but it didn't do any thing.

CdnoilRAM 02-05-2012 09:47 PM

I'm a firm believer in the sledgehammer repair method... But I have no ideas to help you on this one.

starquestbd22 02-05-2012 11:02 PM

I'm not sure what all that fuse covers but unless you are absolutely 100% certain that it is good, I would replace it. I don't know how many times I have checked a fuse and thought it looked fine only to replace it and solve the problem.

If it isn't the fuse then I would think it's either in the wiring/power to the fan control switch, the switch itself, the wiring/power to the fan motor, or the fan motor itself. The motor is easy to remove. Of course, it's visible under the passenger side of the dash and it only has one plug and three screws in a triangular layout holding it in. If you remove it and don't find anything obvious, I would probably test the wiring/plug that connects to the motor with a voltmeter or similar voltage checker. You can try a simple 12V checker but I don't know if the fan motor actually get's 12V or not. I would assume that it gets more voltage the higher you turn the speed but that's just a guess. If you check the power and have a voltage that varies as you turn the fan speed control or if you have 12V constant going to it, then I would say the motor is bad. If you have no power to the motor then obviously I would back up and start testing the wiring that carries power to the speed control switch. Just my thoughts....hope it helps!

willysmith 02-06-2012 12:09 AM

I will check these items tomorrow as I can and it is a very logical method you give here, I have top notch Fluke meters so I should be able to test the fan motor easily because I saw in another post a video link showing how to remove the fan. He was performing some type of modification to the filter, but I couldnt tell what the mod was...! Thanks for the help, I will get back with results.

willysmith 02-06-2012 09:44 PM

ok----Just got home....cold!! I tested the fuse under the hood and it was good, but I also swapped it with a different 40 amp fuse from another slot that I know was working. I tested the fuse socket to make sure I had power at the fuse block;;; all ok. I removed the fan motor and tested the socet and had power to the fan and tested grounds. Hooked fan direct to battery and it runs fine. Put back together....therefore it must be the fan speed selector switch as it is the only item left. I do not know how to access the back of the swtich behind the radio panel or I would have tested, replaced it. Have power to fan motor it runs when hooked to batttery, so must be the control swich, right!? :-) If you can tell me how to get to the switch for test and replacing, great, or else I have to do what I hate the most which is take it to a dealer! YIKES!

starquestbd22 02-06-2012 11:48 PM

Just stumbled cross something you might want to explains how the fan receives different voltages to vary the speed and it also could be your problem. Have you tried your fan in the truck on all speed settings (low-high)?

Also, here's a video on repair/replacement if this part on youtube.

And lastly, if you still feel the need to check the control switch I think this video might help you get it out. It's for stereo removal but it shows how to get the trim piece that holds the switches off. I think the dash should look like yours.

willysmith 02-07-2012 02:43 PM

Thank you Starquestbd22, I really appreciate these vids!! I will go from here and see what I can find out. How can I tell if the resistor is good or bad? Should I have current in that plug with turning of the fan speed selector switch that varies? I am going to go test for current at the plug now. :-)

starquestbd22 02-07-2012 06:40 PM

From what I have read, yes, you should have varying current on the plug that runs to the fan motor as you select different speeds. The control switch apparently selects a different resistor for each setting which would change the voltage and the fan speed. You should be able to test that. Also, apparently if the resistor board fails your fan motor may still work on the highest setting or it may run on high no matter what the selected setting is. I don't think that's a guarantee but it's certainly possible because if the circuit lost it's resistance it would deliver full voltage all the time.

I would say your best bet now is to test the voltage going into and out of the resistor board unit. If you have power in and none out or a constant voltage no matter what speed setting you have selected I would guess its the resistor. If you don't have any going in at all I would say it's the control switch. But you said you had power on that fan motor plug earlier so that makes me think the switch is working.

willysmith 02-07-2012 08:18 PM

OK, I took the dash apart to get the switch out and went to the dealer. He and I talked it over and he said that the switch is mechanical and it almost NEVER goes bad. He thinks it is prolly the resistor and (after I told him the fan plug was cracked and burnt like it got hot and there was corrosion on the ground wire in the plug) could easily be a bad wire/connection there at the fan motor plug causing the problem. Anyway, I ordered the two parts and tomorrow I will go at it again! I dont understand something....the power plug to the fan has two wires and I get voltage there(notwithstanding the corrosion /connection - it may not be going through the plug to the fan, but is present in the wiring), but when I check the resistor plug, it has 8-5 vdc on one leg(of four) and moving the switch doesn't change it, except for the full high position where I get zero vdc! Does the current go to the fan and then to the resistor and back into the fan? I would think the current should go to the resistor and then to the fan. oh well, learning as we go!!
Again THANKS for your help!

willysmith 02-08-2012 03:40 PM

OK Geat! I am all fixed! Thanks to Starquestbd22 and CdnoilRAM for helping me! I was a little taken aback at the dealer's prices for the resistor and plug....$122 and $40 respectively, but heck they have to make a buck too! Anyway, it was the resistor and bad plug at fault so now I am warm again! THANKS!

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