Jeeezzzz...

i see car fire in someone's future...

 

Lol, any suggestions as to what he can check to get the fan to work property?

 

Repeat after me, I'll only do this with a fuse as the first thing closest to the battery. If you are not sure how to wire it up don't even try or it's likely you might cause a bigger problem than you are trying to temporarily fix !!!
And yes, no fuse can be a good starting point for a car fire.

Battery, fuse, wire running to inside of car to switch, switch, wire running to the fan. The fan should already have a ground but if it does not and you are connecting at the fans connector then you need to run the wire to ground. Remember to test it for polarity as it is direct current, meaning you can hook it up backwards and the fan will still work it's just turning the wrong direction (blowing from inside the engine compartment to the outside).

 

As for the gauge of wire, look at the wire going to the fan and go at least one size fatter, bigger. The reason for the relay is to be able to make a shorter run of the wire carrying the heavy current for the fan. Just like add on fog lights. They want to make the run for the wire feeding the fan as short as possible and then use much lighter gauge wire for the control circuit that turns the relay on to power up the fan. Since you will be making the circuit longer adding resistance to it you need to increase the wire size to lower that resistance which would also keep it from building heat inside the wire.

 

Thanks for the advice. I actually wired it up last night. 12-gauge wire from the battery to a fuse, from the fuse to a switch, and then from the switch to the proper polarity of the fan (blowing from outside to inside), with the other pole of the fan grounded. I do have extra wire I don't need, so I'll detach it for now and wire it up with the shortest distances later today.

I drove for about 45 minutes last night with the fan on. The temp gauge never got above the 3 o'clock mark, just like normal. It seemed to drive fine, too--no losses of power (although it was never a very powerful car), no smoking, no boiling over, and the coolant level stayed at the same place. Maybe I got lucky and the engine isn't warped.

I'll try it in the commute tomorrow and see what happens. This time if it overheats, I'll turn it off immediately and get AAA to tow me home.

Still no clue why the factory setup isn't working properly, but this takes some of the pressure off. Maybe I'll try the thermostat and the coolant temp sensor. All the troubleshooting seemed to indicate the relay, but with a new relay in there it doesn't seem likely that that's the problem.

 

BTW, the switch is under the hood of the car for now. If it looks like it's going to be there for a while, I'll redo the setup with a switch mounted to one of the blank switches in the dash, so I don't have to run the fan constantly while I drive.

 

I emailed FCP last night, detailing the problem and the tests I've done to isolate the relay. They called me today, and had no hesitation in saying that they thought the relay they sent me may have been a dud. They're sending a replacement.

I'll use the manual switch for the fan in the meantime, and update the thread when I get the replacement relay.

 

Would the switch make a difference? Wouldn't want you to get a light weight switch that would over heat.

 

How many amps does the fan draw?

 

I'm not sure but I would guess around 10 or a little less and I'd fuse it for 20 as it will spike when it first starts up.

 

OK, i went back and read this whole thread.

Based on what you said in post #1 and #9, here's my guess:

1. From post #1: This is first time you've driven this car in the summer (SoCal summer no-less) heat so you probably didn't notice before this event that your aux fan never worked.
2. From post #9: Sounds like you have pwr to the relay (clicks) and really doubt you've had two bad relays. Once you activate the relay (by grounding either ylw or ylw/wht wire) the fan should work. And since you've hot-wired the fan (proving it does work), that only leaves the wiring from the relay to the fan. PO probably dicked with it and messed it up. I would ck into that.

If you're going to do stuff like this yourself you really should get, at a minimum, a test light, and preferably a VOM, and learn how to use them. If you had, you would have had this figured out in about 10 minutes.

 

I have it wired up with a 20-amp switch, and a 25-amp fuse at the moment. I tried a 15 amp fuse, but it blew as soon as I flipped the switch--probably that power spike that Kiss is talking about. Ideally, it would be a 20-amp fuse, but I didn't have any of those handy, and neither Radio Shack or the local hardware store had any either. I'll pick a few up from O'Reilly later today.

I actually do have a volt/ohm meter, which is how I verified that I'm getting 12 amps (edit: this should say "12 VOLTS") to the power cord that goes to the relay. No test light, but I figured the VOM would do everything the test light could and more. Despite the VOM, though, I'm truly puzzled by this. I don't think it can be the wire from the fan to the relay, because I'm using the entire length of that wire when I have the fan hard-wired to the battery, and the connector plugs securely into the relay (it's such a good fit that it's actually kind of difficult to plug it in).

And although it is technically only 10 days into summer, it's been hot here for months, and I've commuted through worse traffic than I saw the other day in comparable heat. So it's not a matter of that being the first time the fan would have needed to come on to keep the car cool. Beyond that, the car stayed cool in traffic for a while, then suddenly spiked and overheated in a matter of about one-to-two minutes, just long enough for me to get off the freeway by the time it boiled over. So I'm pretty sure the fan failed mid-trip last week.

I agree that it's unlikely I've had two bad relays (unless you consider my luck, that is), but FCP already shipped out a new one, and I'll have it mid-way through next week. So I'll give it a try.

Just to recap, I get 12 amps through the power connector to the relay, the entire length of wire between the fan and the relay conducts power fine when connected to the battery instead of the relay, and grounding the ECU connection prongs should have ruled out the wiring from the ECU to the relay or the ECU itself. So that's where it stands now.

Again, I really appreciate all the help. I've used the site (and MVS) for all the other repairs I've done--including some complicated ones, like the timing belt and the odometer gear--but I've never started a thread until this one. The combined knowledge that you guys (and girls, maybe?) have is an invaluable resource to a car-owner-on-a-budget like myself, and I'm truly grateful to be living in the Internet Age when this type of long-distance discussion is possible. But I guess I'm preaching to the choir here

 

Well something is not adding up...

When you said "12 amps" did you mean "12 volts"?

Good, you have VOM. Do you know how to diagnose problems using voltage drop method? Here's a how-to link FYI:
Diagnosing Voltage Drops - Electrical Automotive Troubleshooting

and a vid:
http://www.youtube.com/watch?v=Ixe0hkcl6dw


You want most (virtually all) of the voltage drop across your load, the fan in this case.

 

I did mean volts. All the talk about amps earlier in the post must have tricked me. I'll go back and edit it.

But you're generally right to question my skills. I do have a VOM, but my knowledge on how to use it is limited to touching the probes to whatever I'm dealing with and watching the needle (it's an ancient analog model) jump. In this case I knew enough to switch it to "DCV 15" and it showed 12v.

Thanks for the links. I'll check them out before I get back under the hood.

 

I got the replacement relay from FCP today, and it solved the problem. Hooray for me! So they sent me a faulty relay the first time, which is a relief.

For anybody who might be interested, here's a link to my companion thread at MVS: http://www.matthewsvolvosite.com/for...247681#p247681

And a link to a pictured tutorial on how to change the relay: http://www.matthewsvolvosite.com/for...hp?f=1&t=37034

Thank again, to everybody, for all the good help.

 

You are welcome and I'm very happy for you.

 

Nothing worse than a bad new part because you end up looking everywhere else for the problem under your nose !!