Window motors need help.
 

I have a 83 240d none of the windows work. I have replaced the switches and the relay. I have voltage to the door when motor is disconnected, but when I connect it I get nothing. Haven't quite been able to figure this out I'm not that good with electrical work.

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In my '79 (not sure if it's the same in other years), you have both wires going to the motor getting 12v when the key is on. My driver side window wasn't working and I found that I had no ground at the switch.

Again, not sure how later 240s are wired, but IIRC I had the hot wire to the window switch that provided power to the entire switch, and sent constant 12v to both sides of the motors. I was missing a ground on my driver side switch, but the rear window still worked because it grounded out from the window switch in the back door.

Where are you measuring voltage?

You are not mentioning the condition of the 2 high amp Fuses that go to the switches and motors.
I had a good looking window fuse until I pulled it and found that the tip was burned or eroded off. The strip was not melted but it was not making contact due to the tip being gone.

Note that the Relay also has a separate fuse. On my year and model it is #12 on the fuse chart.

Also check to see that one side of the fuses is also getting + voltage.
I had a situation where one of the wires that went to a whole row of fuses had become unsoldered. That whole row did not get voltage on either side of the fuse.

There is a fuse chart at this site for an 82 240D: https://www.autogenius.info/mercedes-e-class-w123-240d-1982-fuse-box-diagram/

Right at the door connection.

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Are you measuring voltage across the 2 terminals at the door connection? Those should both be 12v hot when the key is on, so measuring across those two will net you a 0v reading. You should ground out your voltmeter to a known ground, like the door check strap or the door latch.

Digital volt meters pickup stray voltage and can cloud diagnosis. Always use a incandescent test light not a LED as LED can pick up strays.

Basically there is a high resistance in the circuit that makes it look like you have voltage without a load but when a load is placed on the circuit, there isn't enough amperage.

Think of a garden hose that has a kink, the pressure will be high when the nozzle is closed but as soon as you open it, pressure drops and flow is minimal.

As was mentioned, the two leads normally have 12V, measured to a good ground. If one wire is cold, it's probably broken in the door post.



When the switch is flipped, one or the other lead will be switched to ground. If this isn't happening, then either the switch is bad or it has a bad ground.

Our guy has high resistance in the circuit, that is why he has voltage with the motor disconnected and no voltage when the motor is connected.

I don't think he's measuring correctly. The motor has 12V on both leads. So how would voltage go to zero? I think Maximan's post was to the point.

I am working under the presumption that, with the wire unplugged / plugged in, the OP is measuring across the harness that connects to the motor , is cycling the switch and observing a reading on his test equipment.

I will give that his statement " but when I connect it I get nothing. " is a bit vague and the " I get nothing " could mean no motor operation. Given he is testing for voltage, I take it as the voltage goes away when the motor it plugged in and switch operated.

Applying + 12V ( Or - 12V though I don't ever recall seeing this ) to both sides of the motor when in a non operational state then lifting one and grounding it when in operation performs 2 functions.

First it makes switches slightly less complicated because only one circuit needs to change state for a function.

The second less obvious function is shorting motor leads just after dropping the switch stalls the motor to prevent coasting / overshoot. As a motor is coasting down, it is acting as a generator so applying an electrical load creates mechanical load.

I'd apply power / ground directly to the motor terminals and see if it operates, reverse polarity to change direction as well . Use long wires so you don't get caught in the linkage and just brush the final connection in case there is a dead short. A fused / circuit breaker in the test leads is a god idea but sometimes we cheat.

OP should pull up the wiring diagram to better understand it. But what you say is what I also recall. (Here is link to one for my 85 300D)

On my car, the problem was that an internal thermal fuse in the motor had blown. Should be able to test by feeding 12v to motor directly. It is a special fuse that is not easily replaced. But can be. A junkyard motor may be easier! There are threads here about those fuses and the motors.

http://www.peachparts.com/shopforum/diesel-discussion/318503-repair-your-failed-w124-window-regulator-motor-maybe-others-too.html

http://www.peachparts.com/shopforum/2956367-post16.html

This is true in the case of a fan or blower, which have considerable momentum and can coast for some time. But when a window motor reaches the end of it's travel, it's stopped dead, so it can't become a generator. At that point, it becomes an inductive load which consumes electricity and produces heat. The heat will trigger a thermal switch which breaks power in case the switch isn't released. When the switch opens, stored energy in the motor winding is either dumped back into the harness as a reverse spike or released as heat.

You are forgetting about a partial window movement where motor becoming a generator is relevent.

Think about the person that wants the now closed window open just a crack for air. Down , overshoot , up overshoot to fully closed, down . . . . Darn car. . .

A stalled brush type motor powered by DC is a restive load rather than an inductive load. It would be inductive only at initial power up / power off.

If this same stalled motor was powered by AC, there would be an inductive as well as a restive load. If this was a permanent magnet brush motor, the inductive load would go away once the " permanent " magnets became demagnetized. Winding failure might occur prior to this happening though.

At old job, we were stall testing 1 to 2 HP 90 VDC motors on 180 VDC. Every once in a while, the permanent magnets would flip polarity and motor would run in reverse.

From what I recall, some motors would run faster after a test due to field weakening but lose torque in the process.

IIRC, the gearbox that goes on the window motor is driven by a worm gear, so the window motors literally cannot act as a generator in these cars.

For what it's worth, I've never encountered a car where the window motor acted as a generator before.

You are forgetting about armature inertia.
Granted, window regulator / track friction can be high enough to limit travel so we are not talking about inches of travel.

Why do you feel that 12 V+ is supplied to both terminals of the motor when no movement is requested?

Hopefully Turbo has or will soon just trouble shoot his window electrics. This thread has gone off track with very unlikely scenarios.

Check fuses, relays, motor, switches, wiring using meter, 12v supply and wiring diagram. Many here have done that.

Not sure about the 240D, but on my 300D, the power supply to the switches/motors is connected in pairs. Front left & Rear right and vice versa. So if passenger rear works and driver front does not, at least you know that power is being supplied. Moves trouble shooting to next step.

Your theory is correct, but it’s not relevant to this application. The window motor produces a tiny fraction of a horsepower, turns at maybe 500 rpm, and drives a complex mechanism with high friction loads. There isn’t enough residual motion to provide much generated power, so essentially no braking force. The problem you describe is one of hand/eye coordination.

If the mechanism stops due to friction braking, so does the armature. When there’s no motion, no current is generated. All the mechanical energy is dissipated as heat.

As for 12v+ on both leads, it’s the way every Benz is wired. It reduces by one the number of conductors over the next simplest scheme. It also snubs the inductive kick which occurs when the motor stops dead due to mechanical braking.

Just to be sure 240D is same as my 300D, checked 240D wiring diagram. As can be seen below, Fuse Fb feed both sides of motor when switch is in neutral position.

Meter across motor terminals should read ~zeroV with switch in neutral. Then +12V or -12V when switch is actuated up/down. Same if wires are first disconnected from motor.

If you do see +/- 12V and motor doesn't run, take motor out. Replave or open it up and check the thermal overload fuse. Then test motor while out with fuse jumpered. Some have left fuse jumpered and re-installed. If you do that be careful not to hold switch down too long!

Can someone tell me how many gear teeth on the rear window motor in a coupe (1983 300CD)?

Okay so I fixed my windows, broken wires in the doors, but now I can't get my hood open I already tried manually opening the latch through the hood. The drivers side released but the passenger side won't give. Any ideas on how to get it open.

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On a 97 E320 / W210 I've used a long screwdriver ( like 3 ft long ) to pop a latch from under the car.

I am just going to throw this in. I don't like to use incandescent test lights because when the time comes to use one the bulb is often shot and it is often difficult to find good ground for it near where you are using the light. I prefer a volt meter because it tells me how many volts I am getting. I have found that to be of the most use most of the time.

I admit I had a Car battery fail and it showed 12 Volts but had so little current that it barley would spark if you shorted a cross the Battery Terminals and that is how I found out it was no good.
In that particular case a working test light would have helped.

What exactly did you do to fix the windows?

All 4 Doors had broken wires?

There is some threads on the hood not opening issue I remember none of the details. It has been several years since I have seen someone post with that problem.

Using a volt meter on an electronic circuit board fed by a well regulated power supply will work. However , a car has a unregulated supply and long wire runs. This makes for " yep, the voltage is slightly low but is it due to a fault or normal resistance? " .

Some thing amiss here as there's only _one_ hood latch on a 1982 W123 so how can only one side of the hood be opening / .

-Nate

My knowledge is only from actual experience. I have no theory or other electronics knowledge.

I mean if I was checking + wire to the Window and I had 12 volts instead of 12.50 volts due to wire resistance I would deem that enough voltage ao allow the window to work.

However, I recently had a problem on my Chevy Van Window. In this case there was some but not all of the wire strands broken (about 1/3 of the strands broken on 2 different wires) and that apparently caused enough resistance in the Window Switch and I eventually had smoke coming out of the Switch. The Window only worked intermittently and finally not at all.

Since the broken strands were near the connectors I ran a bead of Solder on each wire to the connector allowing a good circuit and an New Switch and that fixed it.

In that case although it was trouble shot without an Meter or Test Light I would have been showing good voltage and it is likely the Test Light would have also worked fine as the Test Light would not need a lot of current.

"The drivers side released but the passenger side won't give" I believe that the inside hood release is the drivers side and the front hood release/tab is on the passenger side."

On mine once you pull the inside hood release of you go outside and pull up on the hood the Tab/release extends making it easier to grab.

In the past some have had the mechanism that operates when you pull the tab malfunction.

You can look it up on this forum where you buy parts. I wouldn't count on a new motor matching your regulator because any 123 regulator ccould have been swapped it.


@Turbo, try pushing down on the hood above the latch that won't release. You may need a helper to pull from inside. You need to releive the pressure so that the latch can retract.