Derale 16749 question

[Kaptain Kadian]

I am running dual electric fans on my 70 c10 with a derale 16749 thermostat. Today, I went to start my truck for the 1st time in a while, and noticed that 1 of the fans came on immediately when I turned the key to on. It isn't supposed to come on until the coolant has cycled and the truck has warmed up. The next problem was that the other fan never came on. I adjusted the setting in the thermostat to see if I could get it to come on and it never would. They both had been working properly the last time I checked them. I had another sensor that you insert into the fins of the radiator, so I hooked it up to see what happened, and neither came on. This was what I expected since I didn't insert it into the radiator. So, I figured I have a bad temperature probe, but seems weird, because I have had it for about a year and have barely driven it. So, do you think it is just a bad probe? I don't have time to strip the wiring on the 2 fans to hook each up to a battery to test them tonight, but that will be my next step. I don't know the voltage if the fans, but I am wondering if the thermostat is capable of powering both of them. It had ran both fine for a while, so I am not sure. Any other ideas of how to check them? I hope a while just came lose or something with the other fan.

[Ruscal]

You could check the fans by just jumping them. If they are all right you would expect something in the controller or wiring. I have the Derale PWM controller on mine. I elected not to use the radiator probe sender due to inconsistent contact possibly causing issues. Instead I used a temp sender mounted into an inline radiator hose temp sender mount mounted down near the lower radiator outlet. It has been working well now for about 7 months. You have to remember to ground the sender adapter since it is floating on the hose.
Russ

[davepl]

I don't know your truck, but does it have modern AC? If so it could have an AC trinary switch in the system that kicks at least one fan on as soon as the compressor starts. It's a longshot, but easy to overlook, so figured I'd mention it...

[Kaptain Kadian]

Originally Posted by Ruscal

You could check the fans by just jumping them. If they are all right you would expect something in the controller or wiring. I have the Derale PWM controller on mine. I elected not to use the radiator probe sender due to inconsistent contact possibly causing issues. Instead I used a temp sender mounted into an inline radiator hose temp sender mount mounted down near the lower radiator outlet. It has been working well now for about 7 months. You have to remember to ground the sender adapter since it is floating on the hose.
Russ

Thanks. I have pm'd you before about issues I have had with it. I have a little more info. I stripped the wires to the fan that wasn't working and jumped it to a battery and it came on. They both also came on when I wired them back together and jumped the green override wire to the battery. I don't have the ac override wire hooked up right now. I also have mine hooked up to an inline radiator adapter on the inlet radiator house. Mine is not grounded though. I didn't see a way to ground it when I installed it.

[Kaptain Kadian]

Found the grounding threads. I guess I will ground it and see what happens. It is weird that it worked fine for a while and now is messing up if it is just the ground on the adapter. Thanks. I will report back. I have to get a new battery 1st. After 6 years of barely driving it, it bought the farm.