Heater blower motor melting relays

[dieselnutjob]

A few months back the heater fan packed up in the 806.  It would sometimes start working again if you drove fast enough, and when it did there was a funny rattling noise.  Then it totally died.

 

So I bought a replacement fan, and fitted it.

 

This also didn't work.

 

After further investigation I found that the relay which feeds power to the thing had died and the relay socket was looking a bit burned.  I bought a replacement from Halfords and after bending the pins a bit to increase the clamping force on the most burned spade in the socket, it worked.

 

I think that the rattling noise might have been the relay chattering.

 

Six months later it died again.

 

This is the replacement relay.

 

 

The relay is fed by a 30 amp fuse which is correct and not blowing.

 

I think that the fan is pulling about 25 amps on full power which seems a lot.  My ammeter runs out at 10 amps, so I set it to draw about 10 amps with the relay replaced with a long bit of thick wire, and measured the voltage drop on the wire, then set to full fan speed and measured the voltage drop on the wire again which had just over doubled, but was dropping nearly two volts going into the fan, so with 20 amps at 12V I reckon 25 amps max at 14V ??

 

Is 25 amps a lot for a blower motor?

 

I put a different relay in from Halfords which clearly says 40A on it but it does get uncomfortably hot to touch with the blower on full power.

 

So now I am wondering whether it was a rubbish relay or two bad fan motors in a row, which seems unlikely.

 

I'm going to keep the old fan as a 350 watt 12V motor seems like a potentially interesting thing to have.

[twosmoke300]

Check your cabin filter . 307s melt the heater resistor wiring when the pollen filters get blocked

[2MB]

Does it work on all speeds when it works or just the higher ones? No idea if these cars have a resistor pack but a faulty one of those can cause similar issues

[Dead_E23]

25 amps sounds a lot, but the size of the fuse suggests that the motor's supposed to do that!    

 

I wouldn't be too astonished if I bought a relay from Halfords and it subsequently turned out to be of less than superb construction.   Might be interesting to open that up and see if the contacts look like big chunky 40A jobbies or weedy tinfoil.  Do relays have a duty-cycle type rating?  No idea.

[Bren]

I have had success in the past with bacofoil.

[castros_bro]

Hi Fans.

 

The big fuse is because when first switched on the fan motor is not turning so is a "dead short" to the power, but as it gathers speed it produces a "back EMF" because it is  acting as a generator the same time as a motor,  and the current reduces. The running current should be a lot lower then the starting current.  The usual reason a fan motor takes too much running current is something mechanical is restricting its spinning, ie  it is spinning slower then it should so not producing enough "back EMF" therefor taking too much current. Restricton in the airflow, filters,  blocked pipe work or extra motor friction of borked bearings or fan rubbing on housing will all cause it to spin slower and take too much running current. 25 amp running with 40amp start sounds ok but I check for some restriction - usually impossible as everything is built into the dashboard.