Extract fan failure

whazza22 · Jun 20, 2012

Hi everyone,

I have a fault on an industrial extract fan unit in a plantroom.

The unit consists on 2 fans, a pcb mounted on the side and an isolator. The fan is linked to a trend bms system.

When the fan unit is switched to hand on the control panel, one of the fans runs for about 5 seconds. Then one of the relays de-energise and the fan fail light comes on. The contractor and the other 4 relays stay energised. Therefore causing the fan to stop.

I have checked both fans and they aren't seized, however one is slightly stiffer than the other (not the one that starts running though).

Has anyone got an ideas what the problem could be? Someone mentioned a faulty flag switch but can seem to find one.

Thanks

snowhead · Jun 20, 2012

Air flow switch not detecting the first fan moving air and failing or PCB faulty causing the same symptoms

whazza22 · Jun 20, 2012

Where would the air flow switch be as I have looked in the unit and cannot see one? I have also looked along the ducting :S

whazza22 · Jun 20, 2012

Also, there is a light on the control panel for flow failure so I'm assuming that would be lit if the sensor picked up a flow problen

TheatreSparks · Jun 20, 2012

One thought is that the fan unit is shutting down due to a thermal sensor in the motor winding thinking that the motor is over temperature, this may feed back to the PCB and giving a fault output which is been fed back to the control panel, thus giving the fan-fail light.
Is there a change over system to switch between fan motors on a back-up type of arrangement which should cause the other motor to kick on?

whazza22 · Jun 20, 2012

There should be an automatic change over incorporated on the pcb for some reason it doesnt. The fans plug into the back of the pcb do cannot switch over manually. Both quick blow fuses for the fans on the pcb are fine. Possibly a faulty pcb but looks ok.

TheatreSparks · Jun 20, 2012

Just wondering what connections there are on the PCB? If there are some form of output connections then it is likely that is what is bringing on the fan-fail light. The fact that they don;t switch over automatically would possibly indicate a PCB fail or the other fan motor is faulty. Any indication what causes the change over to occur?