Radiator Fans won't go!!???

JCoop · #1 (**permalink**) 08-21-2006, 04:59 AM

I finished a relay mod for my CAV ignition switch to alleviate a load problem that overheats the switch when the A/C and headlights, then the fans, go on during hot summer nights. It basically takes some load off the switch. However, when I did the mod, everything was good except the radiator fans wouldn't go at the designated temperature ( I have a programmable SPAL controller hooked up to 2 X 12" SPAL fans). Even with the override switch, I can only hear the fan relay clicking. I thought it was low voltage, I charged the battery, but still just clicking of the relay. Is that a symptom of bad ground? Or maybe a bad relay?

Thanks IA

mn12 · #2 (**permalink**) 08-22-2006, 08:13 AM

If you can hear the relay click I might suspect bad ground to the fans but you should be able to test the voltage coming from the relay easy enough with a multimeter to be sure

JCoop · #3 (**permalink**) 08-22-2006, 01:53 PM

What I meant by the relay clicking was not just 1 click, as in contact made; rather a continous clicking like the electromagnet doesn't get enough juice to make the contacts stick...

mn12 · #4 (**permalink**) 08-22-2006, 02:07 PM

Ahhh. Could still be a ground issue for the relay or even a low voltage on the positive side

Dangerous Doug · #5 (**permalink**) 08-22-2006, 03:08 PM

Sounds like the relay is turning off and on, and the fan doesn't get a chance to get started. Take a look at the signal you are using to turn the relay on. My money is on a low DC voltage with higher voltage noise "spikes" on the line. The spikes in the signal are turning on the relay momentarily. You'd need a low-pass filter on the switch, which is essentially a small capacitor in parallel with the switch. If you're using a DMM to look at the signal, the Vdc will filter out the spikes, but should be able to see the dc voltage. Switch it to frequency measurements to see if you're picking up an AC noise signal. Good time for an oscilloscope, if you've got one available.

Oh, and if your ground wire is exceptionally long (i.e. a small antenna), you may be picking up the noise there. Check the ground connetion and keep the wire short.

I used to be an Applications Engineer for Tektronix.

JCoop · #6 (**permalink**) 09-05-2006, 05:06 AM

Thanks Guys,
Problem solved...well sort of. When I first started troubleshooting, I saw the 30A fuse on the fuseblock designated for the fans was melting but not blown. After I installed the relay at the ignition switch, I replaced that fuse with a 25A. Yesterday, I just decided to replace it with a new 30A and viola, the fans worked, although I didn't go for a road test. This tells me there's something screwy with this circuit...and the fuse isn't doing what it's supposed to do.

Any ideas?

rlearp · #7 (**permalink**) 09-05-2006, 06:19 AM

Ray,

get out your multimeter and measure the currently directly when the fans are on. I've measured a lot of electric fans over the last couple of years on the race cars to make sure I've got enough wire gauge to handle the load. I've never measured one over about 9 amps continuous, and these are some 14" and larger good quality fans.

If you've got two fans find out why they are drawing so much current. Or, if it isn't the fans get them off the circuit they are sharing with other accesories that are drawing the current.

I know there was a thread on www.gt40s.com regarding the ignition switch sharing power with the AC compressor clutch etc. Your situation might be similar, it seems the CAVs have some screwy wiring in some builds.

I'd start checking those fans and find the true current draw. And if the fans aren't the problem through that circuit I'd find out what is drawing the juice. Might post again over on GT40s.com too, but put it in the electrical section, I bet it'll get more response. Not everyone reads the CAV section there.

R

JCoop · #8 (**permalink**) 09-05-2006, 10:51 AM

Thanks Ron,

Actually, I had posted on a thread started by Dave Briggs I think, regarding "...fun with relays" .
You're right, the guys at http://www.gt40s.com are very responsive. I'd be lost without that resource. I got all my missing wiring diagrams and more from Veeks, Bob Childress, and a ton of helpful responses with my CAV woes.

JCoop · #9 (**permalink**) 09-06-2006, 03:03 PM

Only the fans are hooked up to that fuse terminal.
So if a 25A fuse can't carry enough current to get the relay to work, and a 30A fuse will - but heat up enough to melt the plastic, that tells me the wiring for the circuit is marginal at best. But if I increase the wiring capacity (12 ga. instead of 16 ga.) That would blow the fuse everytime the fans kicked in, no? Sorry, my brain cells just aren't ampere-friendly.