looking for ign on circuit for intercooler fan

I have my intercooler fan wired through a relay, with a switch on the signal side of the relay. I have the relay signal powered off the ignition on circuit from the ign switch that provides power to the in car fuse block. Problem is that everytime I switch on the fan, it blows the 60 amp underhood fuse. I'm not sure why the relay would draw enough current to do that, but does anyone know of a better ignition on circuit to go to?

I would need to know the year/engine size to look up the wiring diagram for your car. Also would you happen to know what the amperage draw of your fan is. If you have an amp shunt or amp meter in the 30 amp range you would be able to measure it. It would not suprise me if the fan draws somewhere around 15-18 amps in which case you should install its own fuse or fuse link. Throwing an extra 15 amps on that 60 amp circuit may be putting it over the top. I am assuming the load side of the relay (fan), is wired and fused by that 60 amp fuse that is blowing....

I just thought of something else. Check to make sure all the terminals on your relay are isolated from ground. Some relays come from the factory with a terminal already terminated to ground to aid in wiring it in. If by chance you have that kind of relay and dont know it, you can easily short B+ to ground when you wire it in. Throwing the toggle switch would immediately blow your 60 amp fuse. Just something else it could be that would be a simple fix.

The car is a 95 3.8. The power to the fan has its own fused curcuit from a free terminal on the high current box, as well as its own ground. The relay has four terminals: signal in, ground, power in, and power out. The signal in circuit is the one I am having trouble with. Only thing I can think of is that it is drawing too much current at the ground going back to the battery. That doesn't make sense to me though, because EVERYTHING grounds back to the battery, and all my gauges, PCM, and other electronics don't blow and they have a common ground.

Your electrical schematic (non SC model) shows the 60 amp fuse supplies power to the Intergrated Relay Control Module (IRCM) located in front of the passenger side wheel well. I would assume any unused terminal in the IRCM that is used for an accessory would add to the load on that 60 amp fuse. It would have too. I would temporarily hook the fan wire with fuse directly to the battery or just leave it off completely. Now if you Still blow that 60 amp fuse you have a *defective relay*.
I really would like to know if your relay has a suppression diode in it. Relay manufactures will enclose a suppression diode wired across the coil to clamp spikes caused by the release of the coil. Relays in their strict sense do not have a "signal in" and "ground". They just have 2 coil wires. The only time they will have polarity is if they have snubbers or spike diodes. Thats why I said *defective* relay. It just may be that there is a spike diode in it and the polarity is reversed-which would blow your fuse....

MN12 may still have some instructions on his site for the intercooler fan/relay hook-up. However, on mine (94) I took the relay power off the threaded buss on the inside face of the under hood fuse box (just pull up the sliding cover), so it was always hot. Then I powered the relay switch off one of the ignition controlled circuits on the regular inside fuse box. Worked fine for years, plus I also put a fuse in-line to the fan motor itself.

I used the sensor wire off the radiator overflow as a trigger because it's close. On my '94, it was the purple wire. I put the relay in front of the radiator upper support, next to the ground screws and a fuse from the bottom terminals of the fuse block, where the battery connects.

Jackie, the power comes straight from the battery. Nothing comes directly from the IRCM. The signal to the relay goes from the red wire out of the ignition switch that goes to activate the ign-on circuits in the dash fuse panel. My tap-in runs to a switch, then the relay, and the relay grounds to the common ground on the header panel just in front of the battery. the fan power comes from the battery, through an in-line fuse, to the relay, out of the relay, and to the fan. As soon as I activate it the buss fuse blows. I can check it with a different relay to see if it has an internal short. I doubt these relays have an internal diode, as they cost me 8 dollars at Radio Shack. Also, because my 20 amp radiator fan (aftermarket universal) keeps blowing 30 amp relays. it comes on a couple times without drama, then ceases to come on again. I assume it spikes when it shuts off and that blows the relay. I will go to the electronics supply store tomorrow and get a 30 amp diode for it to solve that problem.

Jim, I looked at MN12, his power comes from the ign circuit and his signal comes from EEC power. I think thats worse than my setup. Actually, mine is very close to yours. What circuit is your relay signal coming from and where does the ground go? Mine is on the same ground as the fan ground, but again I don't think that should matter since everything goes to the battery anyway. The whole car is a ground.

Do you have one of those directional diodes on your relay?

I can't rmemeber, its been awhile, but the wiring connector I got with some generic relays I bought on ebay. I don't remember what post it was connected to, but I eneded up removing them from all my relays.

The diode is to keep transient voltage from going back in the direction it came. I can't remember if the diode was on the enrgizing side or the energized size. You might try removing that diode if there's one there.

what kinda of IC fan is it? If its the 8" permacool, you should be fine...

Nope, no diode, but I will put one on the power side so I don't blow that relay when I get it working. And yes, it is the 8" Permacool.

Regarding why your relays may not last more than a few cycles, it could be because of inrush current. I am not trying to make something more complicated than it really is but when you make your relay selection you need to factor in "inrush current". On something like a DC fan with brushes, when power is first applied, the current sky-rockets until the fan blade starts to turn. The inrush current could easily be 3 times the running current. This inrush only appears for less than a second but the relay sees it. So a relay rated at say 30 amps may handle 30 amps but it may not be able to withstand a higher inrush. Take a look at this automotive cube relay. Go to Mouser.com and in search field enter 653-G8JN1C7TMFRDC12. Then click on the Mouser part number. Now Click on "DATA SHEET" . Nice small cube automotive relay with an insulated bracket. This is a 35 amp automotive cube relay that has an inrush current of 100amps. Pop the cover on one of your burned out relays and look at the contact arms. If they are blue or twisted from heat, it may be from inrush current.

I got the relay problem fixed today. I finally found a strong enough diode and installed it. The fan would turn on, but would spike current back to the relay and burn it out when the fan shuts off. I also went ahead and gave my intercooler fan it own circuit. I turned it on and blew the same 60 amp fuse again. now I am very confused since I drew power for the switch from an empty terminal on the underhood fuse box that is separate from the fuse that blew.

Sorry you have not resolved your problem yet. Lets back up. Earlier I thought: [The car is a 95 3.8. The power to the fan has its own fused curcuit from a free terminal on the high current box, as well as its own ground.] also: [the power comes straight from the battery] but today you gave the intercooler fan its own circuit? I thought all this time it had its own circuit. When you say "high current box" what exactly and where is this box. We must be thinking of two different boxes. Since the fan has its own inline fuse you can tap upstream at a point that is not fused. What you want to do is select a non fused point. Install your inline fuse at that point. Proceed and run wire from fuse to relay. Then from relay to fan. Dont install the fuse close to the fan. If you do, you won't be protecting the wire from the inline fuse all the way back to your tap point. No shortcuts here. Always install the fuse at the tap point. This way it protects anything downstream that can go wrong. It protects the wire, and relay from burning up if something should go wrong. This is very important. If the fuse is at the fan, with no upstream fuse, keep a fire extinguisher in your car because your asking for trouble.

Unless the relay your buying is a Solid State relay, a diode is not doing anything to protect your relay. It doesn't work like that. Diodes are placed in parallel with the coil of the relay to clamp spikes created by the relay itself and to prevent damage to sensitive electronic relay controllers. You should not have to clamp the fan motor for spikes. The relay is already protecting itself along with upstream devices. Once the relay releases or opens, any motor spikes from spin down are going nowhere,... because the relay is Open.

Would you have the Radio Shack part number of the relay your buying. I will look it up and see why this is not working for you. I have a feeling your taping in downstream of that 60 amp fuse somehow. Whats messing us up is I don't know exactly what you mean by "high current box" and I need to see what relay your using. Review the Data Sheet at Mouser Electronics. Inrush currents are important.

I can get carried away at times because I use to teach electronics. Its important to understand "why" when things go wrong. Hang in there. The painful journey makes the goal even better.

Jackie, sorry if I was unclear earlier. I'll draw up a picture of the way I have it now and get it on here in a few minutes. My radiator fan problem is fixed, the diode took care of it. Now I am just working on the intercooler fan.

Here is a diagram of how it is set up. As a side note these connections are accurate per the diagrams that came with the components, and I verified power at all the terminals and continuity at all grounds. A thought I had, I wonder if it has something to do with having both grounds going to the main ground. Shouldn't, but I will move them to their own body ground and see what that does.

The reason why your blowing the 60 amp fuses is because your switch is miswired. Disconnect the ground wire on the switch. There should only be two wires going to the switch, Load and Power. The switch your using is SPDT. It has 1 terminal more than you need. By grounding that extra terminal you dead shorted power to ground.

That will resolve the fuses blowing for now and it will look like your good to go but actually you need to apply some of the other points that were brought up
otherwise in time you will be back working on this same circuit.

Jackie999 said:

The reason why your blowing the 60 amp fuses is because your switch is miswired. Disconnect the ground wire on the switch. There should only be two wires going to the switch, Load and Power. The switch your using is SPDT. It has 1 terminal more than you need. By grounding that extra terminal you dead shorted power to ground.

Click to expand...

Yep, this sums it up and will fix the IC fan problem.

Actually, it just dawned on me that you might be using a lighted switch. If it is a lighted switch, you will need to ground the switch. In that case, I'd lean toward the relay being bad.

Yeah, sorry, I forgot to mention it is a lighted switch. I picked up a a new relay the other day. I'll go ahead and stick it in there and see what happens. Before I risk blowing it again, do you think I should go ahead and re-wire the grounds to another location, or am I correct to think that wouldn't matter on a ground?