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I have a Pontiac Grand Am. After getting a hose replaced, I noticed that my fans don't come on now. I checked the fuses and cooling fan #2's fuse is burnt out, which (I think) should be for AC only. It's winter here, so that's not a big deal. So now I'm left wondering why cooling fan #1 isn't coming on when my car is plenty hot. The only thing I see for fan #1 is relays. How can I test these relays? Is it practical to do, or do some auto part stores test relays or anything?

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3 Answers 3

I had to do this recently, like Brian said you'll need a power source and a multimeter. Most relays have a wiring diagram printed on them and most automotive relays are 4 pronged. Two prongs will be your positive and negative power and the other two will be the bridge that is made. What I did, and this was a very very cheap method and suggest for possible risk of electrocution that you try a safer method...I took speaker wire and stripped the ends. I wrapped a wire each around the positive and negative prongs on the relay. Then while touching the multimeter leads (set to test for continuity) to the bridge prongs, I touched the speaker wire to the car battery posts (thus the risk of electrocution, I DONT RECOMMEND THIS AND TAKE NO RESPONSIBILITY IF YOU DECIDE TO DISREGARD MY WARNING). Maybe someone knows a set of clips that will fit a car battery on one end the small alligator clips on the other end. If the you hear a click and have continuity, then the relay is most likely fine. If you only have one of the above or have no click and no continuity, it is probably kaput.

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Why are you assuming that the fuse is only for the AC fan? It seems really strange that only one of the fans would have a fuse on its circuit. Replace the fuse, since you'll have to do it anyway - if the fan still doesn't come on, then start looking at other possible causes.

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Oddly enough, I replaced the fuse and now both fans work –  Earlz Dec 12 '11 at 15:43
    
Not odd at all. You have one fuse for both fans. Same as on my Honda. –  Mike Baranczak Dec 12 '11 at 17:09
    
Yet the fuse was explicitly labeled "COOL FAN #2 FUSE"... Even more odd was a fuse labeled "COOL FAN #2 GND FUSE" which wasn't blown –  Earlz Dec 12 '11 at 17:27
    
Maybe it's just badly labeled? The people who design cars have their off days too, just like everyone else. If you really want to know what's going on, try to find a wiring diagram for your model. –  Mike Baranczak Dec 12 '11 at 17:35

It can be done with a power source and a standard VOM. Apply appropriate power source to appropriate pins while listening for click and looking for the desired effect (could be presence vs. absence of voltage or continuity/lack of) on the VOM which would be attached to the appropriate pins.

You'll want a repair manual to find out what to replace "appropriate" with in the above, especially in regards to power supply and pins...

Also, you need to be very careful and make good connections that can't short out against each other while testing. A typical test involves 12v battery voltage, and it won't go well for you if you accidently short that out... Use good electrical safety practices and caution.

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A simpler way: find another relay of the same type, then swap it in. If that fixes whatever problem you were having, then you know the other relay was bad. Obviously you can't do it if you don't have an identical relay. –  Mike Baranczak Dec 11 '11 at 22:34
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@MikeBaranczak You also risk damaging/destroying a perfectly good relay if the original relay failed through too much current draw so... –  Treffynnon Dec 12 '11 at 16:15
    
Ah. Good point, I haven't thought of that. –  Mike Baranczak Dec 12 '11 at 17:35

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