Chevrolet heater fan issue

[Svslow]

I have a 76 that is completely stock besides this Chevrolet heater fan motor upgrade. Every 5 or 6 days it’ll pop the fuse. I have it grounded two times. Once from the fan to the dash and the other from the fan to the stock ground wire. Any ideas ?

 

[m_m70]

I know mine draws enough amps to make my alt belt squeal bad if I have it on when I start the motor. Learned to make sure its off before and turn on after motor is warm.....hoping serpentine will fix!

I know not much help but good luck with the fix! Someone will chime in with the answer!

 

[gnpenning]

Does the motor spin freely or can you hear it dragging??
Which cage are you using, stock or the gm?

When does it blow?

Have you checked your power wire and switch??

More information is needed

 

[chuckyb]

I'm assuming that the wiring harness is original based on the OP and it sounds like grounding is not the issue. The Chevy motor creates more of a draw than the OEM motor. Assuming the cage is spinning freely as gnpenning suggests, it seems likely that the original wiring to the heater switch and / or motor is the culprit, and getting too hot under load.

 

[SHX669]

what chuckyb said ^^^^ . I had no issue with the Chevy motor conversion and factory '68 wiring --- so I also suspect it's a bad motor or and issue with the supply wiring .

 

[Timmy390]

No issues with my 74 stock wiring and the motor upgrade.....

Tim

 

[DirtDonk]

I've seen this several times over the years. Put the bigger motor in, blow the fuse every now and then.
Answer is the opposite of what we've been taught over the years. Just put a bigger fuse in.

And no, I'm not kidding. If you have a 20a in there now, then install a 25a instead.
The extra 5amps is not enough to melt any wires in the system, and is usually enough to stop the blowing. If a fuse rated at an extra 5a blows though, then you do have to look for more issues. Such as too many accessories on that circuit, failing connections and splices, motor drawing too much current, fuse contacts corroded, etc.

Since you've been replacing fuses the fuse is not corroded, but what about the old contacts in the fuse panel? Are they pristine, or somewhat less than that? If less, then it's time to at the very least take a wire brush to them. If you can twist your neck around enough to see the backside of the panel, look for rust, dust and fur-balls building up. Clean it out the best you can and look for any signs of over-heated wiring like brown areas up near the terminations.

If this is a '70 or older you'd have other issues, but since it's a '76 the fuse panel is slightly more protected up in the glovebox. But it can still get rusty and dusty, so check it out.
In fact, check it all out before you up-rate the fuse just in case. But if all else is in great shape still, those extra few amps won't hurt anything. And you can even go up slightly if you can find fuses rated at different increments. I think they're all 5a increments at that level, but could be worth a look for a 22a or so.

Good luck.

Paul

 

[DirtDonk]

I forgot to "x2" what was said about the old switch too. Sounds like it gets used, so not from sitting is it corroding, but they do get old and might be adding it's own resistance value to the circuit.
While you're twisted around under the dash, reach up and pull the connectors off of the blower switch and inspect for said brown areas of overheating. Then clean the connections and reinstall. That alone could be enough to cure your blown-fuse issue if that's the culprit in the first place.
Saves you from worrying about a higher rated fuse.

Paul

 

[DirtDonk]

And perhaps an alternate work-around until you can fix any old worn out components that might be causing excess drag with the new more powerful motor, would be to swap the wires around on the switch so that LOW speed comes on in the first ON position and HIGH speed comes on in the second ON position.
Stock had the heater blower coming on full blast in the first position and that was always thought of by me to be a way of getting an old tired motor up and running cleanly without drawing too much power. Applying full voltage at first seemed a sensible way of speeding up the starting process. Even though no other vehicle I'd ever seen did it that way.

You could try swapping the Red and Orange wires to see if the problem goes away, remains the same or even gets worse.

Good luck.

paul

 

[Svslow]

Thank you for all the great input. I’m going to clean everything up tomorrow.