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Cooling Fan Relay burning out


chip's Avatar
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07-25-03, 03:55 PM   #1  
chip
Cooling Fan Relay burning out

My car is a 1995 Mercury Tracer. I’ve had to replace the cooling fan relay twice in one year. The relay has four terminals: two on one side are labeled “coil” on the opposite side are a “comm” and “no” terminal. In both instances through a process of elimination I settled on the relay as the problem. Last year the coolant temperature sensor failed a few weeks before the relay. Both last year and today when I pulled the relay, the comm terminal was blackened and the plastic case around it was partially melted. I’m assuming they are shorting out internally. This time around the Ford dealer supplied a relay of a different design. I showed the two previous terminals to the counterman and he shrugged his shoulders, said he had never seen that before, but agreed they must be shorting internally. Is this just bad luck with new parts? Anyway, the fan works again, I can hear the relay click, but it does feel hot to the touch. Should it heat up? Am I overlooking anything here? I don’t subscribe to Alldata so I don’t know if there are an service bulletins pertaining to this. Thanks in advance for any information. I appreciate th great service you provide on this forum.

 
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07-25-03, 03:59 PM   #2  
Joe_F
Alldata's cheap, suggest you for for the 25 bones--a service manual will cost you 3x more.

You don't need a subscription to check bulletin titles--go check and see if anything pertains to your car. If you find one, subscribe or have a Ford dealer print it out for you.

Check the wiring closely, also make sure the fan spins freely. The fan could be putting a drag on things and burning out the relay (high resistance).

 
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07-25-03, 04:44 PM   #3  
chip
Just subscribed to Alldata--nothing there. Wiring looks in good shape. The fan turns freely, compared it with my 2001 Escort. Wait and see I guess. Mya be pure coincidence for two relays to fail in identical ways.

 
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07-25-03, 04:51 PM   #4  
Bad parts do happen sometimes.. How about 4 Mopar fuel pumps into 1 Jeep before it ever left the rack???

 
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07-25-03, 08:37 PM   #5  
i would double check the fan motor even though it functions fine it is often the cause of burning up relays due to pulling to much amperage than what the relay is designed to handle, another spot to check is the actual terminals the relay pushes into to make sure they still fit tight and clean of all corrosion that could also cause excessive heat build up due to high resistance at that connection.

 
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07-25-03, 09:22 PM   #6  
chip
Bejay, actually the terminal the relay pushed into is very corroded or blackened. I just wasn't sure which came first--the burnt relay or the corrosion. I cleaned it as well as I could with electronic spray cleaner and compressed air. I bent the terminal prongs with a small screwdriver to snug them up and put a film of dielectric grease on the new relay ends before pushing it in. The terminal is part of the engine fuse block and I would replace the single corroded terminal if there is a way to pluck it out. Is there a prong inside that releases with a small screwdriver or something like that? Thanks.

 
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07-25-03, 09:45 PM   #7  
replacing the terminal usually isnt an option due to a couple of reasons one being usually the plastic around the terminal is melted and once removed the new terminal if you could find one exactly the same would probably not lock back into place due to the melted plastic locking tab that holds the terminal in place.
a better way of repairing it short of just replacing the fuse box would be relocating the relay outside of the fuse box simply by buying a universal relay in wich you could mount to the fender of the car and you could either use insulated female spade terminals to attach the wiring to the new relay or you can buy a pigtail wich is available for alot of relays that include the connector and about 6 inches of wiring to solder the original wiring into the new connector. if you was going to do this just be sure to buy a high enough amp rated relay to handle the load of the cooling fan.

 
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07-26-03, 06:36 AM   #8  
Joe_F
I can't believe Alldata has NOTHING on your problem.

Have you looked at the electrical schematics for the cooling system? You will likely have to trace out the circuit and look for any anamolies there that might be causing the excess load.

I agree with MSA about the part, but after 4 OEM parts, something's likely wrong .

 
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07-26-03, 05:21 PM   #9  
chip
Thanks to all for the input. Even if a corroded terminal is the root cause of the problem---which I doubt because the fuse block is pretty well sealed---the wiring needs to be examined and tested for what will probably be the underlying problem. I know my limits, so I'll take it to a pro.

 
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07-27-03, 03:24 PM   #10  
trendar
Once that terminal connection starts developing high resistance, it generally turns out to be a vicious cycle of sorts with these high current draw circuits, getting overheated and even higher contact resistance. The second relay probably stopped working because of the poor connection at the terminal- Were you able to bench test the relay to see if it was really bad, and not due to the terminals?
As Bejay mentioned, checking the current draw would be a good idea to make sure that isn't the underlying cause of why it started developing high contact resistance in the first place. Either way, sounds like that connector may have to be sectioned off to restore a tight connection.

 
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07-29-03, 06:30 PM   #11  
chip
I hope you'll humor me with a followup and a dumb question. I took the car in to the shop and the technician determined the fault was the corroded terminal causing a high resistance situation. He opened the fuse block and replaced the burnt terminal. Today I got home after driving with the a/c on for about 40 minutes and the relay was hot to the touch----but then so was the fuse block itself. So I wonder, is it normal for the relay to get hot? I did pull it out and it’s not burned or melted. How much heat does the relay normally generate? Am I overly obsessive, after all the fan works fine.

 
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07-29-03, 07:40 PM   #12  
trendar
Was he able to check the current draw of the fan during operation? If it's normal, and he was able to restore a clean solid connection at the terminal, then it's probably fine-
Some of the heat may just be added from being in the engine compartment, assuming that's where the relay is-
The relay has to pass a lot of current in normal operation, so it'll heat up to a certain extent. If you're able to keep your hand on it it's probably okay.

 
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