When I had fans a long time ago I noticed the drop any time the fans kicked onto high, whether it was from a stop or from low speed. It wasn't quite as bad when they were on low, but it was still there.

I bought a soft start / PWM fan controller from dccontrol instead of using a normal on/off harness and it helped tremendously.

 

They are on my 95. With them in series it will suck a sheet of paper against the grill from a foot away. The stock clutched fan all but didn't spin it was so worn out and the AC always blew cold then and it never ran warm. I think running in series only will be plenty.

 

Just like Thunder550, I only notice a dip in voltage when the fan/fans come on high, when they come on low I wouldn't even know it if it weren't for the led I wired in. The voltage dips for a second then comes right back up.

 

No dip on low, darn. So, do the fans ever go directly from stopped to high? Oh also, how are your fans controlled? 2 pins to the PCM? 1 to the PCM 1 to the A/C clutch?

 

I have the Nelson harness, which uses 1 pin to the PCM and one from the AC clutch. The 2 fans never come on high by themselves, only when they are already on low and the AC compressor engages. When the AC compressor clutch engages and the fans aren't on low, only one fan comes on high. Doesn't seem to affect the voltage too much from what I remember (haven't driven my truck in a few months since the trans broke )

 

Thanks for the help, my condolences on the truck. Hopefully it will be back on the road soon.

 

Upgrading the alternator to a 140a or 180a would help a lot too i think. I have a 2500HD which I think comes with the 140a alternator already. I have mine wired with 2 pins and really dont notice when they come on at all....high or low.

 

Mine was with the 140 alt..helped some but never took the drop out completely.

 

The 2 pin setup is what GM uses right? With a 145a alternator, correct? We never hear to much complaining from the people who have the factory GM fans. I'm wondering if most of the complaints about the voltage dropping is coming from the people with the 1pin A/Cpin harnesses or the people who wire it up to control manually.

I would think that by spinning them up in series mode, then switching to parallel once they are up to speed would minimize the shock to the electrical system considerably, probably why GM did it that way. Anyway, just a thought.

Do you run yours as the 2pin hookup? Series/parallel system that GM uses?

Just trying to see who is has problems/complaints with their electric fans and why, especially when you don't hear too much from the people who they came stock for.

 

I'm not sue how GM does it, but initially I ran the Nelson harness with A/C causing one fan to come on high, temp causing both to come on low, and temp and a/c together causing both to come on high.

With the dc control unit they were both wired together. a/c only caused them both to come on 50%, and the speed was variable based on temp.