Hi,
I’ve got a 2001 DRM 3500 (5.9) which, with the help of this forum, has taken me 10s of thousands of miles as a converted camper back and forth across this country several times in the last few years. Thank you for that!
My current issue is that when I run my AC the fan drops my charging voltage. Battery and alternator test fine and everything is good until I turn the AC on. At each fan speed the charging voltage drops more and more to just 12v at highest fan speed. I put in a new fan resistor and same thing. I disconnected resistor and ran fan at high speed and the voltage dropped to 12v again. When fan does run it seems fine- no burning smell or lag or struggle with speed- just the voltage drop which goes too low and runs the battery dead eventually and unable to crank the engine.
Any ideas are greatly appreciated- it’s midsummer and I’m in S. Florida.
Thanks

 

I'm of the mind it might be time for a new fan motor. A clamp meter on the wires would tell you what it's drawing, but it sounds excessive.

 

Might want to check the alternator, It may be putting out voltage but if one or more of the diodes in it are bad the output will drop. Wouldn't be a bad idea to check what the fan is drawling either.

 

Could be a weak belt tensioner, allowing the belt to slip and the alternator to not spin fast enough.

 

All good suggestions...I had this issue in another car I use to have and it was the compressor clutch that was pulling extra power. But thats probably a long shot...

 

Long story short it looks like my original in dash volt meter is screwed up. I'm using one that plugs into the cig. lighter socket for now.

Thanks for your responses.