View Full Version : DC Fan motors

21-03-2017, 12:15 AM
Hi Guys,

Can someone please explain to me why DC condenser fan motors take out the outdoor
Control PCB when they go faulty?
Sometimes they check out fine on resistance readings. Is it something to do with the diodes in the fan motor?
I had one that was supposed to check at .5V DC and it was reading .001

And why do they take out the board even when it has not started up?

I'm no electronics expert, but why don't they have fuses to prevent this?


21-03-2017, 01:16 AM
Maybe they make more profit selling boards than the equipment?,yes we all know how to protect stuff but manufacturers don't adhere to common sense,they maximise profits on spares.

27-03-2017, 09:42 AM
Yeah true true

27-03-2017, 09:47 AM
But does anyone have a lot of experience with them and why they take out control boards etc?
Units are getting too expensive to repair with all these chain reactions from pcb board to pcb board.
They say this new technology is to save power and the environment but how does it do this when your throwing away 5-7 year old machines as its more economical to buy a new one with warranty.
This means the factories making these will be working overtime using even more power and pollution to make more units.
Just trying to self learn how to fault find all this electronics.

28-04-2017, 06:23 AM
this post was about a month ago, but I hope the following helps

a DC fan motor normally has a PCB inside that converts the 300Vdc to 3 phase, just like a common inverter that runs the inverter compressor.

so the plug depending on the brand would have 300VDC and a GND, a speed input (0-12VDC) and a speed output (pulses from a Hall effect sensor)
common faults are a short in the transistors that run the motor, if short on the input side you can sometimes measure it with a multi meter, other times they can go short on the output side, this would typically show as a stiff motor.

now it depends on the brands, some are more robust then others.
The fan motor will have 300 VDC applied and not run, until a drive signal is sent, it is at this point that it can damage the pCB eventhough it measured fine.
some manufacturers are so bad that they have developed a test kit that can actually test run the motor...

hope this helps

29-05-2017, 09:53 PM
Hi mate,

Could you tell me please which manufacturers have a test kit for checking dc fan motors?

02-06-2017, 11:34 AM
Thanks very much for the reply Steph, very helpful!