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Old PB 100 Electric Radiator Fans

G

GGM63

New member
1989 PB100 with a VM Diesel. It has dual electric radiator fans which have quit. As a result it overheats. All the docs I have show this model (and everything close) with mechanical fan. Im trying to figure out how it was wired and what the problem is.There is no power to the fans on the current wiring. I have checked at start up and as the engine reaches temp. When I jumper the fans directly from the battery they work fine. I can't locate a switch or relay that obviously control the fans. Anybody have any information or ideas ? Thanks
 
I'm not familiar with Pisten Bullys, or with VM Diesel engines, so take this with a (large) grain of salt...

Generally, electric fans are set up to turn on and off based on temperature. On a computer-controlled engine those temperatures can be programmed in the computer. For example, maybe on at 186º and off at 176º. With two fans you would normally program one fan to come on at one temperature range and the second fan would turn on at a higher temperature range.

Without a computer, I suspect there is a temperature switch located strategically in the cooling system to turn the fans on and off. I think it's one temperature. That is, above the threshold value the fans turn on, and below that value they turn off. If that temperature switch is broken they won't turn on.

Electric fans can be relatively high-draw in terms of amperage, and it would make sense to use the temperature switch to turn on a relay rather than run all the amperage through the switch. But if someone removed the stock fan setup and installed the electric fans without much forethought, who knows what electrical buffoonery they're capable of...

My understanding is mechanical fans move more air than electric fans, but they take more power from the engine to do so. In an automotive application, once the vehicle is up to speed there is usually enough air passing through the radiator that fans aren't required. But in a snowcat application, that's not the case.
 
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