Electric fan control question

Whaler · #1 (**permalink**) 08-24-2003, 10:29 AM

Hi all
Sorting out my car. Now has 345 miles on it and noticed it getting hot yesterday 100-105 C
So I was close to home and whipped into the garage to notice the electric fan not on.

Troubleshooting began

1) Overide switch had no effect, but isolated switch was good with a meter on ohms
2) Fan worked with 12 volts supplied to it directly sourced into the inline fuse
3) 30 amp fan relay worked well and also had the 12 volts supply to it.
4) 30 amp- inline fuse to fan motor was intact (load)

So after an hour, I went to the last and most obvious, the fan control fuse in my wiring harnesses fuse block. Sure as heck the 20 amp fuse in the block was open. Replaced it and fan worked both in auto temp control and manual overide.

So here's my question, the fan motor (load) has an inline 30 amp fuse, the seperate adjustable thermostatic control cct. has a 30 amp relay in it's block. But my wiring harnesses fuse block has a 20 amp fuse which opened.......

Is it undersized? It's there to protect wiring.
Why did it blow?
Can I go to 25 or 30 amps? To match the other components protection. This fuce that opened really is in the control side not the load side, am I correct? Therefore should it see higher currents? Could it open if the fan runs too much? Looks like the fan cam off when the temp got down to 80 C after replacement of the fuse with the car still warm

Lastly, I do not know what my 16 inch puller fan is drawing when on or what initial start in-rush current is either.

Thoughts?

Tim

petek · #2 (**permalink**) 08-24-2003, 10:56 AM

*IF* the harness wiring is consistant with the fan (probably 14 awg, maybe 12 awg) then going to a 30 amp fuse won't hurt a thing and will still protect the wiring. If it was me, I'd go with a 25 amp fuse and see if it holds ok.

Another option would be to use a 20 amp circuit breaker rather than a fuse. Most automotive circuit breakers work by passing the current through a bi-metalic strip. As more current is drawn the strip heats up. If too much current is drawn the strip is heated to the point that it breaks contact. The neat thing about thermal circuit breakers is that you don't have to worry about in-rush current (as the current doesn't last long enough to create enough heat to pop the breaker).

I've only once blown a 20 amp fuse with my fan. The fan had stalled (insulation holding the fan blade) and the fuse blew. Not having any 20 amp fuses on hand, I replaced the blown fuse with a 25 amp fuse. I don't expect the fuse to blow again ... unless I stall the fan again!

Whaler · #3 (**permalink**) 08-24-2003, 12:47 PM

Hello Pete
I am glad an electrical guy jumped in to answer this.
Here's something to think about. I went back out to the garage this morning to troubleshoot this a little more. I also had bought 20 and 25 amp fuses for trial.
For history sake I have yet to ever leave the car's battery hooked up on the positive if its going to sit parked in the garage. Well last night I left it hooked up.
Today I turn on the keyswitch to see if I can run the fan manually and I get nothing? I also notice my voltage gage hardly even budging. It usually jumps to battery voltage.

So surely I checked the battery with my meter and have 6 volts????? Optima redtop

Battery is on the charger for now.

Standing there and scratching my head I wonder where to start.
Obviously I have a load when the battery is connected. So for first test I hook up the charger to the battery cables on the car to chaeck for a current flow. With the key switch in off I show .35 amps. With the keyswitch on I show about .7 amps
Now I test that fan in manual and I get about 8 amps draw dropping to 7.5
I stab the brakes and I show a 5 to 6 amp draw for brake lights.

Next I look to the fuse panel and start to remove and replace fuses one at a time looking for a difference. Trying to determine what cct is drawing this current?

Is this a coincidence that my battery drained overnight just after replacing that fuse, or is it simply I have another small problem. Funny thing is the battery took little time to recharge to 11 or 12 volts. A load test may be another story when I go to start it

It has in the past been left connected overnight when it was in the alignment shop at a dealership for 2 days. No drain then.

How would you troubleshoot this Pete? Its pretty simple harness not alot of loads/ccts. What should a car be drawing if there really is nothing on parked and ignition off. I have no radio or clock. No alarm.

*As for the fan I have put a 20 A. back in and will see if it lasts. Forgot to mention that yesterday on initial checks for the fan, the 30 amp relay in the thrermostat unit didn't seem seated all the way. Thought imediately that was the problem, but it was the fuse afterall

Tim

Whaler · #4 (**permalink**) 08-24-2003, 01:38 PM

Went out to see if it started. It did.
Put a 20 amp fuse in ( original size)
Went for a drive.......fuse was burnt open when I got home.
took out the fuse and put my meter in to check current. It sees 15-16 amps on initial start of fan and then drops to 9-10 A when it's running. I guess I try the 25 amp next see if it stays?
Lastly I put the meter between the battery and the positive feed cable to see if there was a draw now. It showed 1.8 Amps with the car sitting hot and everything switched off, with the key switch on, it jumped to 2.25 A.

This is going to be interesting, will go back to pulling individual fuses at the block and looking over the wiring

Whaler · #5 (**permalink**) 08-24-2003, 02:16 PM

All fuses pulled and no diff. Last thing I went to pop off was the 4 pin plug on my external voltage reg and that was it. No more drain.
Its showing 2 amps now with the regulator plugged in
Likely stuck on and its one of the cheap ones not a Ford OEM
Tomorrow I will go get a Ford jobbie.
I guess these guys are solid state not mechanical so tapping it shouldn't unstick it. Charging was/is fine at 13.8 to 14 volts.

Tim

Jack21 · #6 (**permalink**) 08-24-2003, 05:22 PM

Petek is great with electrical issues.

The fan control relay takes power from the battery, through a breaker (I also like breakers better than fuses), and powers the fan. A control circuit turns the fan on/off based on the fan thermostat "completing the ground" when ON temperature is reached, and OFF when the water temp falls below a preset limit. It's also a good idea to include a manual fan ON in concert with the thermostat so the fan can be turned on manually. (I like having the fan stay on when I'm stuck in traffic on a hot day, so it doesn't cycle on and off). This control circuit carries just enough amperage to turn the fan relay on and off. Very little. If you're blowing fuses on the control side, check for shorts along the wiring length.

The only thing that uses electricity with the power off should be the sterio settings memory. Not very much. If more, you have other problems. A sticking alternator regulator leaving the alternator energized with the power off. (I used a Delco 12SI alternator to avoid this).

petek · #7 (**permalink**) 08-24-2003, 05:32 PM

Tim,

Looks like you've got this stuff figured out! The way to find a current draw is to do what you did, remove fuses and see what happens.

(Great description of the fan electrics, Jack.)

A bad voltage regulator would explain why the battery went dead and maybe explain the fuse blowing. If the regulator was shot it wouldn't be out of the ordinary for the electrical system to go to say 16 volts or so. Greater the voltage, the greater the current to the fan (resistance staying constant).

I'd replace the v-reg and go with a 25 amp fuse and see if everything works out.

Whaler · #8 (**permalink**) 08-24-2003, 07:27 PM

Hi guys thx for the replies.

Out there kicking this around again in the garage. Seems the highest I recall seeing on the voltmeter while driving was 14 plus volts.
With the battery resting, it's 11.7 volts this moment. When I start the fan manually I have seen 17 to 18.5 amps repeatedly on inrush or initial current but once running though it's 10-11 amps draw. So theoretically we could see 22.7 amps when using the 14 volts running How long would a 20 amp fuse last then?
11.7V/18.5A =14V/ xA
x=22.7 amps

Isn't the rule of thumb to oversize fuses for about 20% or 1/3 more than normal draw? So if it spikes to 18.5 amps with 11.7 volts what will we see at 14 volts driving?

As for tracing out the wire it looks ok. Nothing obviously damaged or compromised.

Last question.

Can a voltage regulator suffer if plugged in under power (with the engine running). I ask this because 2 weeks ago, I had low voltage on the gage and had a look under the hood ( lucky hunch) and sure enough the wheel alignment boys had bumped off the 4 pin plug to the regulator. I plugged it back in while running and it showed good charging to 14 plus volts. Could this have spiked it?? Its also the same weekend it managed to be left overnight with the battery hooked up at the dealership. Problems since??

Tim

trularin · #9 (**permalink**) 08-25-2003, 05:03 AM

Sometimes I select a fuse based on time. A fuse of higher amperage will take a little longer to blow and can allow things to settle.

This should not be run with as overheating wiring can burn down a car.

Just my $0.02

Whaler · #10 (**permalink**) 08-25-2003, 09:01 AM

I would love to be able to use a slo-blo, do they make slo blo style fuses for these type of fuses? I agree I prefer a 20 A slo blo too
Heading out now to buy a new voltage reg.
Tim

petek · #11 (**permalink**) 08-25-2003, 09:08 AM

Yup, you can fry a v-reg by plugging it in while power is connected. Kinda a luck of the draw thing, sometimes ok, sometimes all the magic smoke comes out.

A slo-blo fuse would be perfect, but a 25A fuse should work just fine.

Whaler · #12 (**permalink**) 08-25-2003, 09:08 AM

I would love to be able to use a slo-blo, do they make slo blo style fuses for these blade-type of fuses? I agree I prefer a 20 A slo blo too. How about using a cct breaker in a spade type that replaces the 20 amp original

http://www.bussauto.com/products/circprot/

Heading out now to buy a new voltage reg. and look into this too
Tim

trularin · #13 (**permalink**) 08-25-2003, 09:30 AM

If you are going to replace the regulator ( sounds like you need to ), try to get an electronic one over the discrete component one.

The new electronic ones seem to regulate better and are more forgiving.

I would use the 25 SloBlo or 30 regular.

Just a thought.

Whaler · #14 (**permalink**) 08-25-2003, 09:20 PM

Hi guys
can u belive our ford dealership did no t have a reg in stock....so its here tomorrow.
I have located a 20 amp CCT Brkr for the fan cct.
My cost was 9 bucks ( Cole Hearsey)
I am hoping it can tolerate a spike before it will actually open. If it keeps opening then it's over to a 25 amp fuse.

Thanks again guys for the input...helps alot to kick it around
Tim