Electric fans

[cycleguy55]

Sorry to revive an old thread, but I have a problem with my fans.

Setup: Dual fans (unknown manufacturer), with an adjustable controller. As I posted above, the controller drives the fans through a pair of 40 amp relays. The fans will run after I shut it off, presumably until it's cooled enough for the radiator probe to tell the controller it's cool enough. Like many of these, I have an override switch on the dash so I can cool it down a bit before getting to my destination and shutting it down. That switch has an light to indicate when the fan is running.

A couple of days ago I went to a Show and Shine and, when I got to my spot, the fans ran a LONG time - MUCH longer than they ever have to my recollection even though I had the fan override switch on as I waited for entry and access to my spot. Other than that, everything was fine. When I drove home, I turned the fan override switch on just over 1/2 mile from home. I didn't notice the fans running while driving, but they certainly ran normally once home.

Today, I ran errands and again, turned on the fan override switch for the last bit before going home, but no fans. After I shut the car off the fan override LED remained on, even with the ignition off. Hmmm.... very interesting. I've disconnected and reconnected the battery, and the LED comes back on when the battery is reconnected.

At first I thought the fans had failed - but they're dual fans and it would be a freaky coincidence if they both failed simultaneously.

Then, my thought turned to the relays but, again, dual relays. Regardless, why would the LED light up if were the relays? Unlikely.

So, my thought now is that the fan controller has failed. I haven't tested it yet, but it has power even when the car is off in order to keep the fans running, and the override switch is connected to it through the relay connections.

Does my logic compute? Are these simple fan controllers subject to failure?

P.S. I just turned the dial on the controller a few times, reconnected the battery, and the override switch LED is no longer lit. Turned on the ignition and the fan override switch and there's no fan operation. I haven't tested for power at the relays or the fans yet, but fully believe the problem is with the controller and I've ordered a replacement.

[patrickt]

Originally Posted by cycleguy55

Does my logic compute? Are these simple fan controllers subject to failure?

OK, without seeing a schematic of your setup I'm just shooting from the hip to a certain extent, but "yes" they do fail, and DC motor speed controllers that are PWM can fail more flakily, if that's a word, than say just a plain old big ass resistor. The latter just tends to burn up and not work at all while a PWM is just a big switch that turns on and off really fast. There's also circuitry involved that senses how hard the fans are pushing/drawing because moving hot air when your engine is running hard is completely different from when you just throw your switch on in the garage and proclaim "yep, the fans are working fine." Remember, you only have a couple of components in this little circuit: the fans, the controller, the temperature switch in your radiator hose, the relays and the override switch. Plus the connections everywhere and your little light. I don't think it's the little light. Dual fans can draw a good 30 amps and dual relays are good, and connections are important. If I were diagnosing this in the garage I would do a voltage drop test along the circuit to see if there was any unusual resistance and then I would immediately suspect the controller. I would bypass the controller so the fans were controlled by the temperature switch in the radiator hose and the manual switch exclusively -- and they only have one setting when running, "full blast." Then I would drive it a few times and if everything was fine I would just replace the controller. But if the temperature switch in the radiator hose won't trigger properly then check that it has a good ground and good connection to the relays and just replace it. You can always test it with a VOM and a pot of water on the stove if you are so inclined. But your problem is going to be one of those components. I promise.

[cycleguy55]

Originally Posted by patrickt

OK, without seeing a schematic of your setup I'm just shooting from the hip to a certain extent, but "yes" they do fail, and DC motor speed controllers that are PWM can fail more flakily, if that's a word, than say just a plain old big ass resistor. The latter just tends to burn up and not work at all while a PWM is just a big switch that turns on and off really fast. There's also circuitry involved that senses how hard the fans are pushing/drawing because moving hot air when your engine is running hard is completely different from when you just throw your switch on in the garage and proclaim "yep, the fans are working fine." Remember, you only have a couple of components in this little circuit: the fans, the controller, the temperature switch in your radiator hose, the relays and the override switch. Plus the connections everywhere and your little light. I don't think it's the little light. Dual fans can draw a good 30 amps and dual relays are good, and connections are important. If I were diagnosing this in the garage I would do a voltage drop test along the circuit to see if there was any unusual resistance and then I would immediately suspect the controller. I would bypass the controller so the fans were controlled by the temperature switch in the radiator hose and the manual switch exclusively -- and they only have one setting when running, "full blast." Then I would drive it a few times and if everything was fine I would just replace the controller. But if the temperature switch in the radiator hose won't trigger properly then check that it has a good ground and good connection to the relays and just replace it. You can always test it with a VOM and a pot of water on the stove if you are so inclined. But your problem is going to be one of those components. I promise.

While I've thought of going to a switch / sensor in the lower radiator hose (or tank), my controller has an attached probe that goes in the radiator fins, so I can't bypass the controller and use just the "temperature switch in the radiator hose". I'll take your suggestion to test it in a pot of water using a VOM, though.

Thanks.

[patrickt]

Originally Posted by cycleguy55

While I've thought of going to a switch / sensor in the lower radiator hose (or tank), my controller has an attached probe that goes in the radiator fins, so I can't bypass the controller and use just the "temperature switch in the radiator hose". I'll take your suggestion to test it in a pot of water using a VOM, though.

OK, I would suspect a probe that you stick in to the fins as well. I would think your controller would have some sort of port or plug that let you use a temp sensor in the hose like mine below. They're much more reliable.

[cycleguy55]

Originally Posted by patrickt

OK, I would suspect a probe that you stick in to the fins as well. I would think your controller would have some sort of port or plug that let you use a temp sensor in the hose like mine below. They're much more reliable.

I've thought about going to that setup. Will have to add it to my to-do list.