W124 320CE rear window not working

[col320ce]

Cleaned and tested - no good

Shorted out the thermal overload and bingo!

Any ideas on the thermal unit - replace? or just bypass and keep fingers crossed?

Any idea what the specifications of the thermal overload unit will be? I would prefer to replace if I can get the part.

Thanks for all the help so far too ...

 

[Dec]

No idea from me on that, I often wonder how exactly a window motor knows when it is at the top /bottom of its travel and switches off (total closure)

As its faulty you might as well take it out and see what you can do with it. Personally I would try the bypass to see what happends.

Dec

 

[television]

The idea for the thermal trip is to stop the window motor from overloading and burning out, in the event of someones head sticking out and the window raised so that the head becomes detached from the body.

You know that the protection is not there so just take care with it, and it will be fine

 

[col320ce]

Thanks very much Malcolm and Dec

Sorted. Back in the car still shorted. All greassed up.

Will keep an eye out for a thermal overload unit but not too bothered, will just be careful.

 

[television]

It is only a current trip, and any type would do,,but you would need to know the regular current drawn by the motor, so if the motor used say 4 amps in the worst conditions, a 5 amp trip would do

 

[Dec]

Thanks for the feed back, that’s another one for the knowledge base. Out if interest, how dose the window behave when closed in the usual way… dose the motor cut out when the glass gets to the end of its travel or will it keep going while your finger is still on the switch.
Not suggesting that you burn out the motor but holding the switch for a tenth of a second after glass has reached the end of its travel wouldn’t do any damage.

Dec

 

[television]

I knew that you were going to ask this.

On the later cars with memories where the windows need to be re set,,they have a turn counter, on the early 208 cars,,the memory pack could loose count and they had to be replaced or programmed.

In this car and others like it,,the cut out overload is a device that re sets within 3 sec. there is nothing else. the stall current change on a motor with brushes is near instant.

Thats the way that I see it

 

[Dec]

I often wonder how exactly a window motor knows when it is at the top /bottom of its travel and switches off (total closure)

Thanks Malcolm, that seems logical alright, so because he now has no thermal cut out, Cols repaired motor will burn out if he continues to hold the switch, say for 10 seconds, after the glass as reached the top/bottom of its travel.
That would then explain a lot of other similar failures.

Dec

 

[col320ce]

If I was clever I would have measured the resistance through the motor - measured from the incomming leads. I measured the resistance through the copper coil (to check the copper was not broken) but this will have a relatively low resistance compaired to going through the brushes as well.

With the resistance I measured I get a silly result ... but with the correct resistance we could work out the correct current.

v=ir
v=~13 volts
r=0.9 ohms
=>i=14 amps!

far too high a current, but I would have to remove the trim to re measure the resistance ...

 

[television]

If I was clever I would have measured the resistance through the motor - measured from the incomming leads. I measured the resistance through the copper coil (to check the copper was not broken) but this will have a relatively low resistance compaired to going through the brushes as well.

With the resistance I measured I get a silly result ... but with the correct resistance we could work out the correct current.

v=ir
v=~13 volts
r=0.9 ohms
=>i=14 amps!

far too high a current, but I would have to remove the trim to re measure the resistance ...

This is not an easy calculation,,it comes under transformer design, you have to take account of the induced fields and many other things, the current will also vary with the load, hence windows stopping ½ way up

 

[col320ce]

Does anyone know how the convenience function works? I assume if I have the drivers door window down and lock the car using the convenience function then I actually could burn out the rear window without the thermal/current trip? Or does the convenience function know which windows have been used and only wind these up?

 

[television]

Yes there is the danger of doing this,,I will have a look to see if there is an add on type that you could use, do you still have the old one

 

[col320ce]

Thanks. Yes I still have the old one - still on the motor - I just shorted across the contacts ...