Hydraulic Fan: Vovo G740B

[Championized]

The hyd. fan is running at top speed as soon as the engine is started, even when cold. I've disconnected each sensor (charge air, rad. intake, and hyd.) one at a time, but with no effect. If I disconnect the fan control unit the fan returns to normal speed, but I don't believe this proves it's the fan control. I suspect it could still be in the ECU. Has anybody else had this problem and if so, what was the fault?

Thanks, Steve

 

[Championized]

Apparently unplugging the sensors doesn't prove anything either as it turns out they are normally closed. Disconnecting creates an open circuit.
I've ordered the sensors and will have to change them out to determine which one it is.

 

[cps]

Hi there, Dont know much (ok any thing) about the graders, but on the loaders the hydraulic fans speed can be changed with the contronic units (Volvo tools) for differant climates! Has any one from the dealer been working at the machine lately and maybe changed by mistake??

Just a thought!

 

[Championized]

Hi, CPS No one has been working on it. Just decided to have a fit on it's own. Thanks anyway.

 

[MitchSA]

The fan will blow at rull rpm if one of the sensors fail, sort of a fail safe. The electronic side of the cooling is a stand alone unit with its own sensors which give feedback to the fan control unit. I can get the specs for the sensors from work if you have not solved it by now.

Mitch