Heater control unit

[mb450]

Hi Folks,

Looking for some help with my heater control unit(s).

My first one burnt out - so I replaced it with a used - but in good nick one from a breakers.
I smelt burning on when I turned the fans on today and upon removing the dash top the second one has now suffered the same fate at the first.







With the dash off I tried jiggling the wires in the connector and I managed to get the heater fan to run again but within seconds the wire that coresponds to the burnt out part of the connector was too hot to touch.

Is this a symptom of someting else being wrong?
Partially seized fan or someting else?

Does anyone know if it's possible to get a replacement pair of connectors that I could then resolder in or is it more likely that this component is the one causing the grief:

:-(

Matt

[Cider Andy]

That's a common power transistor that's easily replaced, but I doubt it's the culprit. I think the motor is probably seizing and drawing an overcurrent, as per your suspicion.

Try running a feed direct to the motor to see if the wire gets warm and to see if the fan sounds healthy and fast enough.

It's also possible that both speed controllers were on the verge of failure and that it's just a coincidence.

[mb450]

I will try putting some power across the fan. Where is the fan located?

[Cider Andy]

It's a real pig. It's mounted in a housing that's riveted and bonded into place high in the passenger footwell. You should at least be able to find the wiring but if the motor is about to seize it's not the easiest place to access.

[mb450]

Thanks Andy, do you know what the blower is from if it does need to be replaced?

[mb450]

Hi Andy I think I'm being a bit thick - I've just had my head in the footwell and I can't see the blower at all - to be honest I'm not entirely sure when I'm looking for.

[mb450]

Ok found it! I've cut all the sealant off round the cover and I can see the blower if I lie in the footwell and prise the cover away. How is the blower attached - does the cover come off or is it just a flap?

How is the blower attached - I think it's knackered judging by the black marks (looks like something has burnt out in there)

[peebee]

Sorry to resurrect an old thread but I have suffereed the same problems with the plug on the heater control unit, it has melted around the two leads at one end (one melted completely and the other mis-shapen). I have cleaned up the connectors and plugged them into the contol unit directly and things are working again, but I'm concerned about them getting this hot in the first place. I have searched and found a couple of references to these connectors melting but can't see anyone saying whether this indicates a fault (potential fire hazard?!) or if they naturally run hot.

Matt, in this old thread you were investiagting whether the motor was seizing - did you resolve the issue? My fan sounds healthy enough when it runs.

All your thoughts will be welcomed...

[scotty_d]

I just cut out that burned out pin and by passed it with a heavier cable and it has worked great for the last year. Very easy cheap fix and does the job.

[bobfather]

The comments about this being the motor may be wrong. As I understand it the over heated connector results from a weak terminal connection the PCB. The subsequent overheating and spiking causes the transistor to fail.

Just replace the transistor (you can get them from Maplins) and remake all the terminals with something more robust. There was one PHer who posted that he simply soldered wires to the PCB and used male crimp connectors to remake to the loom

ETA Scotty d, I must be talking about you then!

Edited by bobfather on Saturday 14th February 16:56

[peebee]

Scott, I saw your pics on another thread, thanks. So you think it naturally runs with a higher current than the plastic plug can handle do you?

Sorry Bob, we crossed posting. The fan is now working fine but are you saying that perhaps I need to replace a transistor to stop it continuing to overheat?

Edited by peebee on Saturday 14th February 16:58

[scotty_d]

It does yes but make sure the motor is not sticking which could also cause it to draw more also.

I found if mine ran for long periods the plug would heat up too much so i just fead that wire in and its done the trick. like i said saved me buying a new unit so if i get a few years out it nothing lost.
if it does seize up it should blow the fuse.

Just seen your post Bob i was lucky my transistor was intact so i just cut the loom back to get healthy wire sodered the heavier cable straight on to the PCB and soldered and heat shrinked it.

Edited by scotty_d on Saturday 14th February 17:04

[bobfather]

peebee said:

Sorry Bob, we crossed posting. The fan is now working fine but are you saying that perhaps I need to replace a transistor to stop it continuing to overheat?

No peebee, if the unit works then the transistor will be OK. Sometimes the heat and power spiking that occurs when the connector is failing causes failure of the power transistor. You appear to have caught it in time so you should be OK

Edited by bobfather on Saturday 14th February 17:33