Fan relay heating up

[AA-ron]

Hello everyone,
By chance I touched my fan relay in the fuse panel and found that it was very hot, borderline too hot to touch. I pulled it and did find it to be slightly bulged at one of the terminals. I replaced it assuming it was a bad relay and the new one is doing the same thing. The fan fuse is not popping so I don't believe the fan is drawing too much (20amp fuse and its a 40amp relay). Have any of you experienced this? Am I likely looking for a bad ground? Any insight would be greatly appreciated.

[rich grsc]

Sounds like corrosion of the terminal

[J R Jones]

IMO to create heat power is going through the relay. There are three paths:
* An energized coil. Is the thermal switch energizing the coil? That would indicate high coolant temperature.
* Normally closed (NC) contacts with power applied and have bad contacts (or a bad connection).
* Normally open (NO) contacts that are energized (by the coil), are powered, and have bad contacts (or a bad connection)
When you remove the relay does it click? indicating that it was energized.
jim

[BEAR-AvHistory]

How hot is too hot for a relay?

[egchewy79]

I had a factory relay go bad, leading to my system overheating when the fan quit in traffic and my radiator hose blowing off. Replaced both with AC delco parts

[sread]

I am going thru the exact same scenario at the moment with my car (33 hotrod). In my case I am using the American Auto wire harness and fuse block assembly. 2 weeks ago the fan failed to come on during a drive after running quite a bit because I have it set up to run continuous when the AC is running. I only noticed because I saw the temp start to climb while waiting at red lights after exiting the freeway. The manual override switch did no good so I just stopped for a while to let it cool. After reaching home , inspection revealed the 40A relay got hot and started to melt thru the cover adjacent to the load terminal and even allowed some plastic to drip down into the female socket where the relay plugs in. I have since removed the fuse panel and returned to AAW for inspection and repair. Hopefully it is just a matter of being a poor/loose terminal connection causing high resistance. I am running a Spal fan claimed to draw 25 A which should be no problem running thru a 40A relay.
I will say that AAW prides itself on being a hand made product in the USA and indeed seems to be high quality but I'll be damned if that particular relay doesn't say made in China right on the side. Am still awaiting to see what their inspection reveals.

[AA-ron]

I found the culprit, but its still a bit baffling to me. I cleaned up all the grounds and all is good there. I tested the fan and all is good there. I kept working my way back to where the relay is plugged in and all was good there as well. Then I looked at the short length of wire ( a 2" jumper) that goes between the relay output and the 30amp fan fuse. This wire was getting very hot as it had discolored. I de-pinned it and found that the wire had at some point in it's life, prior to installation, been spun to a point where the wire had become "unwound". Basically, within the insulation, it was a bunch of straight wires. I know from experience that that wire relies on being wound in order to pass current safely. I've seen this before in very short wires. It might only take 2 or three twists to unbundle the wire within the insulation-- especially in something as short at 2". This was apparently creating enough heat and resistance to heat up the relay. Its an odd one for sure. I guess it's been like this since day-one (2 years now) and it just hit the point where it was hot enough for me to notice.
The other scenario is that heat built up in this small jumper wire which caused it to "unbundle". If this is the case, then it's just a symptom and not the cause. I would expect to still see the twists, so I'm betting its the cause and not the symptom. Oh who knows...
I'm bypassing this wire and will test it tonight.

[michael everson]

I have stripped a lot of Automotive wire and have never seen them 'wound' Where have you seen this?
Mike

[AA-ron]

I have stripped a lot of Automotive wire and have never seen them 'wound' Where have you seen this?
Mike

In a previous life I was the Product Development Manager for Boston Acoustics. In one of our divisions we designed and manufactured automotive amplifiers. With out shorter leads (Jumpers) when stranded wire was used, you had to be very carful to not twist the wire because it would lose its ability to conduct current efficiently. If you twisted in one direction, no problem, if the other direction, it would essentially unwind the copper strands and increase resistance substantially. Interestingly, the amperage we were designing around is similar to what this fan draws (25 to 30 amps). I remember melting circuit boards because of this very thing.
I'm not entirely sure that is what happened here in this situation, but its certainly a strong possibility.
Here's hoping that this is all it was and that I don't have some deeper problem lurking within my wiring!

[J R Jones]

Ron, Your wiring methodology may be inspired by something but personally if your fan circuit is protected by a 30amp fuse, I would run the power through the fuse before the relay contacts and on to the fan. You are not protecting all the circuit the way you have described.
BTW on wire twist, I always assumed there is some twist as manufactured. It seems possible that straight strands have higher resistance than twisted strands. That said, the wire could get hot, I do not see how the relay is effected by that.
jim

[AA-ron]

Ron, Your wiring methodology may be inspired by something but personally if your fan circuit is protected by a 30amp fuse, I would run the power through the fuse before the relay contacts and on to the fan. You are not protecting all the circuit the way you have described.
BTW on wire twist, I always assumed there is some twist as manufactured. It seems possible that straight strands have higher resistance than twisted strands. That said, the wire could get hot, I do not see how the relay is effected by that.
jim

Agreed. I haven't changed the wiring diagram from the original Ron Francis configuration, I just ran a test lead temporarily to try to identify why the relay and 2" wire running to the fuse were getting so hot. Last night I replaced that short wire with 10ga and double checked all the connections surrounding the relay. I took her for a spin and the wire gets warm but not enough to concern me. This is a big improvement over the original factory wire (which was getting very hot). The relay still gets hot. I used my temp gun to take a measurement and it read 155 F. I checked the spec on the relay and it's rated for 125 C (257 F). I "guess" I'm comfortable with it being at 155 F, but I will be keeping an eye on it. In any event, I feel better about the larger gauge wire going between the relay and fuse. The wire from the fuse panel to the fan does not heat up, so I think I'm good.
I'd love to know if you all experience a warm fan relay? Its a super easy thing to check as you can reach down and touch while you're driving. My warm/hot to the touch relay may just be a normal thing-- and like many other things, I may have made too much of it. The wire on the other hand, absolutely need to be upgraded/replaced and I'm glad I caught that before it melted.

And it does not escape me that I may win the award for the most boring post of the month... :)

[Railroad]

Now is the time to match up a replacement, write FAN on it and throw it in the glove box.

[CraigS]

Also try different relay brands. At an autocross last year a guy had a dead rad fan due to a dead relay. Several had gathered around and some of those said they will only use Bosch relays. This was 2 guys of 5 so not a big sample but they were both old fa-ts like me so had years of experience messing w/ non standard cars. Slightly related was my experience adding a pusher fan to my car. Spal said it should have a 30amp circuit so I bought a kit supposedly rated at 30A. It kept blowing the fuse. So I upgraded the entire add-on wiring, relay etc to 40A. I went one wire size larger than the charts say to but I haven't blown the fuse yet this summer. I am 'assuming' that the problem was w/ fan startup current draw but not sure why Spal seemed to me to understate the amps required by their fan.