I am having a rather annoying issue with my heater blower. It stopped working completely so I changed the fan speed controller and it all came back to life. On testing the faulty unit I found the output transistor to be blown. After a few days the replacement unit died the same death and again found the output transistor to be blown.

I replaced the output transistor with a higher rated component as the original fitment is now an obsolete part and even then it has died 5 days after fitting it.
Does any one know of any other issues that could be causing the units to blow the transistor?. The relay can be heard to click in but no life from the fan. I am now stuck and its not the easiest part to get in and out as it is buried far back behind the dash.
I would be very grateful if any of you guys have come across this issue and could shed any light.

Thanks

 

Assuming vehicle in question is petrol powered with auto A/C

If the power transistor keeps blowing, I would suspect the blower motor is the problem or possibly a problem with the A/C control panel.

Here are the relative sections of the MY10 Impreza Auto A/C system wiring diagrams






Not sure these will be any use at this juncture but does list the fan voltages for each switch setting
A/C Diagnostics pdf

 

Hello Don thanks for the great information. I will first remove the blower motor and check that out for current draw and bearing smoothness as it was very dusty and the previous owner had no idea of what a cabin filter is judging by the crap that was on it when I changed it.

Thanks again for the great info Don. when I have had some results I will post back just in case people are having the same issue

 

Ok problem solved. well touch wood everything still works. Turns out the current draw from the motor was very irregular but on inspecting the motor brushes they were fine. The problem was the crimps in the power connector for the blower had oxidised quite badle and had slightly spread. So I chopped them out and fitted new spades and hey presto smooth current and working well. Thanks again for the wiring information Don.

 

Glad to hear that it's fixed.

 

So far its worked so i am a happy bunny and in the same day got the steering wheel controls working with the chinese android stereo so a successful (be it minor stuff) kind of day 😁