Fan fail

[Helirich]

I just got Dave's fan Fail relay and his fan relay. (Thank you Dave) I just installed them. I have a couple questions on the whole system.

First weird thing, when I found the fan Fail socket, there was no relay there. Instead it had a wrap of electrical tape. Under it was a three wire jumper. I assume that was some kind of bypass, so I removed it and plugged in Dave's.

I left both fuses out and turned the ignition key to on. Then I turned the AC on and got the double flash of the fan fail. All seemed good, so I turned everything off and installed one fuse. I repeated the earlier test and got the single flash. That part was good, but I didn't hear any fan running.

I turned everything off again and installed the other fuse. When I turned the car and AC on, I had no flash and I hear the fan. I laid down on the floor and confirmed that one fan was not on. I know the fans both worked a few months ago, but I've driven quite abit since then. I'm assuming that one of my fans quit after 40 years. (The nerve)

Anyways, should my fan Fail light be on? What exactly does the fan Fail light tell you?

Funny, I have some new fans coming, but I hadn't planned to install them right away.

[Bitsyncmaster]

My first fan fail units measured the fan currents but I had so many users have problems because the fan currents were not consistent. Some would take some time to settle on a constant current some the start currents would be to high or to low. So I changed to just measure the voltage on the load side of each fuse. If that voltage is below 10.0 volts it will turn on the fan fail light. Even that test has had a few users work with me because the fail light would turn on. But that usually is a bad connection in the power to the fan relay or a bad alternator not putting out enough voltage.

These new fan fails also check if the unit is getting to hot. What produces most of the heat are the fuses. If you get the overheat warning first thing to do is remove and install the fuses again. This seems to be a common problem with fuses running near the rated current. I have counted about 10 owners that have had their fan fail jumpers melt and even start burning. So even if you run jumpers you should remove and install the fuses about once a year. I now ship silver plated fuses in hopes that corrects that problem.

[CFI]

What exactly does the fan Fail light tell you?



It tells you if one of your radiator fans has failed. IIRC it does so by comparing the current going to each fan. If current is lower for one side, it triggered the light.

In theory, it’s handy. In practice, it was poorly executed. The factory relays were garbage. Since power to both radiator fans passed through that relay, if it failed you lost both fans. And worst of all, it wouldn’t tell you that they had both failed!

Some of us have modified the system to be redundant; the fan fail relay is eliminated and each fan has its own relay. That way each relay now only has to deal with half of the load, and a failure of one relay will only stop one fan instead of both.

[Helirich]

What I don't get is, the lights come on in tests, but don't come on with a failed fan. Unless there are certain failures that won't trigger it. I haven't got a chance to see what's wrong with that fan yet. I drove through a ton of water on my way back from Delaware. So maybe it got shorted out or just unplugged.

Is that three wire jumper something that people did to replace bad FF units?

[Bitsyncmaster]

What I don't get is, the lights come on in tests, but don't come on with a failed fan. Unless there are certain failures that won't trigger it. I haven't got a chance to see what's wrong with that fan yet. I drove through a ton of water on my way back from Delaware. So maybe it got shorted out or just unplugged.

Is that three wire jumper something that people did to replace bad FF units?

That jumper was a recall to replace the OE fan fail unit because of high failures.

No my fan fail will only signal a failure if a fuse blows or the fan has low voltage. It does not test fan current. Note if you still have the 40 amp breaker installed the fan fail will not get power and hence no failure light if the the breaker opens.

[Helirich]

That jumper was a recall to replace the OE fan fail unit because of high failures.

No my fan fail will only signal a failure if a fuse blows or the fan has low voltage. It does not test fan current. Note if you still have the 40 amp breaker installed the fan fail will not get power and hence no failure light if the the breaker opens.

Ok, I guess that's better than my trucks fan Fail. It's the temp guage? It has an added warning where it blows steam out the front.

I need to look for the 40 amp breaker.

BTW, I love the fan relay. The delays are so much better!