Heater Blower Switch

[blackbirdxx]

Hi,
I've got the popular problem of both the air con and heater blower motor only working on high rather than on the variable settings. I'm lead to believe that the likely problem is the transistor behind the rotary blower control on the dash. I have removed this blower control and soldered in a new TIP 3055 - T0218 transistor to replace the existing one. After plugging verything back into the dash and after about a minute of operation, smoke starts to appear from the unit and the transistor and metal heat sink gets red hot. The question is, where do I go from now to address the problem. Any assistance will be gratefully received.

[Brucey]

the other common fault is the larger transistor that is mounted near the motor itself; it might be this that is at fault, and causing the other transistor in the rotary control to fail; the two work together and can fail together too.

hth

cheers

[Pod]

+1 on that. Also, make sure that the bearings on the blower motor spindle are well lubricated. They can often dry out. It should spin freely without dragging.

[blackbirdxx]

Hi,
I have a new Bosch fan motor and a new uprated transistor on the bulkhead next to the blower motor. I understand for the motor to only blow on high for aircon and heat is a blower switch problem. Grateful for any replies however!

[Chris Wright]

They are saying something is pulling too current, the likely suspect is a dragging motor/failed heater motor transistor, but you have a new motor/transistor, so check for shorts to ground in the wiring. Pull the harness at both ends and check for continuity to ground in the wiring.

And not to be Capt. Obvious, but you did check that the newly installed transistor is not shorting, right?

[Ed Lyerly]

I'm thinking what Chris said .... something causing too much current to be pulled. Could something be in a bind with the reinstall, so that the blower fan is not free to turn easily ?

[blackbirdxx]

Hi,
Stupid as it sounds but I've now found the cause of the smoke coming from the blower switch. Its the heat sink getting so hot that its melting the plastic case. To recap, I have replaced the failed transistor in the switch to a new TIP 3055 of the same size using the same metal heat sink which is getting so hot it now melts the case and there doesn't appear to be a way I can keep the sink away from the case in order to stop this. I could of course use some heat reflecting tape or something to protect the case but is this a usual problem? Should this transistor and sink get so hot? The blower now seems to work correctly on full and variable speed so the transistor is operating OK.
Anyway, as usual, any assistance gratefully received.

[Ed Lyerly]

Should this transistor and sink get so hot? The blower now seems to work correctly on full and variable speed so the transistor is operating OK.
Anyway, as usual, any assistance gratefully received.

No, it definitely should not get so hot as to melt the case. My best guess is that your variable speed won't work for long ..... and your new TIP 3055 will be ruined, putting you right back where you started
You need determine what is causing the extra amp pull (which is causing the transistor to overheat). Did you somehow put the new fan motor in a bind whan you replaced it ? Blower cages installed incorrectly or possibly rubbing against something that would cause an extra load ???

[horsetan]

Thermal compound paste may also be helpful between the transistor and the heatsink.

[jon-]

I have the same issue, both the air con and regular fan only work on full.

Before I order the wrong bits, is this what I need?

http://cpc.farnell.com/jsp/displayProdu ... 2660286347

Thanks in advanced.

[nick88highline]

I have the same issue, both the air con and regular fan only work on full.

Before I order the wrong bits, is this what I need?

http://cpc.farnell.com/jsp/displayProdu ... 2660286347

Thanks in advanced.

Here are some pictures of a brand new part from BMW showing all the components used. This is the part that sits near the blower motor in the air duct. Someone had butchered my board before and the only thing on it was the transistor. I had to replace it every couple of years, but hopefully this new one will last a bit longer. I also replaced the blower motor control unit behind the control on the dash as this had melted.

<img src="http://farm7.static.flickr.com/6067/605 ... c354_z.jpg" width="640" height="426" alt="IMG_6744">

<img src="http://farm7.static.flickr.com/6193/605 ... 1174_z.jpg" width="640" height="480" alt="IMG_6747">

[Chris Wright]

I have the same issue, both the air con and regular fan only work on full.

Before I order the wrong bits, is this what I need?

http://cpc.farnell.com/jsp/displayProdu ... 2660286347

Thanks in advanced.

Yes, Here is the PDF detailing it:
viewtopic.php?t=14791&

The first link is broken, scroll down to the PDF download.

[pistonboy]

Let me revive this thread with my problem. I have a RHD 1981 635CSI with aircon and my blower control works only on MAX, for both aircon and normal fan. So that means the blower switch is the culprit and probably the transistor needs changing.
The info on this thread relates to a switch that my car does not have. If I can find a clever person to help,I will post pics of my switch.
Can anyone help with info that guides me to fix my switch?