300SDL heater stuck on and blower motor does not work. - Page 2 - PeachParts Mercedes-Benz Forum

Father Of Giants · #16 08-07-2017, 01:12 PM

Quote:

Originally Posted by sixto

I'm with TX, key switch is the next suspect.

Sixto
98 E320s sedan and wagon

How do I repair it?

86-300sdl · #17 08-07-2017, 03:05 PM

Could also be the blower motor regulator (attached photo) located in the fan motor enclosure. See photo.

Also could simply be a loose connection at the blower motor. Mine had a loose feed and showed no juice.

Also unlike '85 and earlier, the PB unit in the 86 SDL is non serviceable i.e. repairing solder joints.

On an '86 there should also be an outboard fuse line located on the passenger side of the fuse box that protects the PBU located exterior to the fuse box.

Also had the "loose / worn" ignition switch the guys are speaking of. Ended up replacing both the switch and tumbler.

Diseasel300 · #18 08-07-2017, 05:48 PM

Since none of the fuses have any power, your key switch is bad. 5, 6, 7, and 8 are all powered from the same auxiliary contact on the key switch. If it goes bad, you won't have power present on any of them. Hopefully you aren't driving the car, your brake lights aren't working either!

There are writeups on this forum (I think in the DIY section even) on replacing the ignition switch assembly. It isn't difficult, but does take some time. The part is not expensive either. It does require removal of the steering lock assembly.

Father Of Giants · #19 08-07-2017, 07:43 PM

Quote:

Originally Posted by Diseasel300

Since none of the fuses have any power, your key switch is bad. 5, 6, 7, and 8 are all powered from the same auxiliary contact on the key switch. If it goes bad, you won't have power present on any of them. Hopefully you aren't driving the car, your brake lights aren't working either!

There are writeups on this forum (I think in the DIY section even) on replacing the ignition switch assembly. It isn't difficult, but does take some time. The part is not expensive either. It does require removal of the steering lock assembly.

I'm very sorry, I mis diagnosed, there is power going to all the relevant fuses, and brake lights are functional. The engine block was dirty so I had to scratch it.

So that means the switch board and blower motor are last suspectsleft? Or could there be more?

Diseasel300 · #20 08-07-2017, 08:39 PM

If you have power on Fuse #5, you should be able to get the ACC to perform some functions. As a simple test, unplug the monovalve and insert your multimeter into the plug. You should read 0V. Go start the car and set the temp wheel to max cold and hit the center button. Go back out and read the voltage at the monovalve plug. You should read battery voltage (12V or higher).

If you do, the ACC is likely working. If you don't, the ACC is likely having problems. It is common for the solder connections to fracture around the pushbuttons. My SDL kept dropping out on rough roads and I found fractured solder connections on 4 of the 5 pushbuttons.

You could also have a failed fan or a failed fan controller. Once you diagnose the ACC, you can move on to those parts.

Father Of Giants · #21 08-08-2017, 10:27 AM

There is full voltage at the monovalve. 13.89v. Time for a new alternator soon?
Back on topic, where do I proceed from here?

Thank you because this help is invaluable.

Diseasel300 · #22 08-08-2017, 10:48 AM

13.89V is fine, means the alternator is working. Above 14V or below 13V is when you begin to worry.

Since you know the monovalve is working, you at least have partial functionality of the ACC pushbutton unit. Now you move on to figure out if your blower regulator or blower motor itself are bad.

I've attached a PDF of your blower power diagram. It has the early and late versions, not sure if your car has the fuse in #16, or the external strip fuse.

You will have to remove the lower dash cover on the passenger side. You'll see a big plastic cover over the fan chamber. The blower regulator and blower motor are inside.

The plug for the blower regulator is on the side of the plastic box. I believe it comes outside the closed area so you can get to it without dropping the blower out. It will have 3 pins in a 4 pin socket. The socket will stay up on the box with a clip, but you can disconnect it and pull it down for easier access.

With the car running, test across terminals 1 and 2. You should read battery voltage. If you don't, go check the fuse for the blower.

Put the ACC in some function mode (EC is good) and set the fan to MAX. Read across terminals 1 and 3. You should measure some value of voltage. Change the fan to MIN and it should change. If you don't read anything, or it doesn't change, the ACC is at fault.

If you do read voltage and it does change when you fiddle with the fan switch, the blower regulator or blower motor are at fault.

Mxfrank · #23 08-08-2017, 02:53 PM

Does this car have an aux water pump? If so, disconnect it's power and see if it makes a difference.

Father Of Giants · #24 08-16-2017, 02:01 PM

I checked the terminals 1 through 3.
With ACC set to O I was reading 0 volts in terminal 1, 13.84±.01 volts in terminal 2, and .100 volts in terminal 3.
With ACC set to EC I got the exact same results.

Bad ACC?

Also upon pulling out the lower dash cover there was this device with a torn wire at the very end of it's connection. It's in the first attachment below.

I'm not too familiar with electronics, but I'm 99% sure I'm supposed to testing this thing in the 2nd attachment correct? If so, then my test is valid.

Should I pull the ACC unit out and see if the wires went south?

Father Of Giants · #25 08-20-2017, 11:02 AM

I took a look at the strip fuse inside the car and it is heavily corroded. So I'll order another one.
Also where is the relay for the blower motor located?

And how exactly do I jump voltage to the blower motor to see if it will spin?...I'm guessing I'm going to have buy some small alligator clip jumpers.....I presume it's like jumping voltage to a car battery only this time it's the motor you want to direct current to.

I would like to mention when I first purchased the car the blower motor worked fine. It would blow out hot air....but as I tried pressing other functions on the ACC the motor starting switching on and off by itself accompanied by this clicking noise. And within seconds it eventually died on me. This leads me to believe the ACC is perhaps toast...I'll upload pics of the ACC's wires and circuit. Along with pictures of the blower motor so you guys can give your opinions on the state of the system.

Something interesting also is that the paper that lists the fuses has the fuse for the blower motor highlighted for some reason. It's the only fuse that's highlighted so it's safe to say that the blower motor may have been a problem in the past.

If I can jump some voltage on the blower motor and it doesn't spin, I'll oil it, dust it, then replace the brushes and see if that helps.

Diseasel300 · #26 08-20-2017, 11:53 AM

The reason #16 fuse is crossed out (not highlighted) is because your car has the external 30A fuse holder for the blower. It will be outside the fusebox, likely zip-tied to the wire bundle near the brake booster. It'll be a square looking box. Open it and the 30A strip fuse is inside it.

There is no relay for the blower motor. Power is switched from the ignition switch directly to the blower motor controller. The blower motor controller is the heatsinked module (porcupine) inside the blower housing.

If the blower worked before, but stopped when you started pushing buttons on the ACC, you likely have one or more broken solder joints on the ACC board. Mine had broken joints on 4 of the 5 mode buttons. Before resoldering, the blower would randomly cutout and back in as the car was driven. Fiddling with the buttons would usually bring it back for a while before dropping out again.

The blower motor can be tested with jumper leads. If you drop the cover to the blower compartment, you'll see the 2 wires plugged into the blower motor itself.

Stack86’300sdl · #27 10-25-2019, 11:39 AM

Good morning all,

Long time reader, first time posting. I have similar problems as mentioned in the thread with the exception of not having power to the #16 fuse. It is still intact and the inline fuse does not appear to have been added. That said, I tested the motor and verified operation. The other fuses power up as they should when the ignition is switched on, but now the auxiliary fan (to monitor temp) only powers on with the defrost button. Does this mean the ACC unit is bad? Could that be the reason there’s no power to the fuse?

Thanks for any and all input.

Stack
86’ 300sdl

Diseasel300 · #28 10-25-2019, 11:55 AM

Sometime in mid 1986 they switched to the in-line fuse holder. If your car is made prior to June 1986 it should still have Fuse 16 populated for the blower. You'd be well advised to mod the power setup to an external fuse holder since the Gen II blower draws a lot of power for those crappy torpedo fuses.

The sampler fan for the climate control is powered from Fuse 5, same as the ACC itself. It should be running any time the key is turned on, regardless of the state of pushbuttons on the ACC.

Power to the blower fuse is from the ignition switch (it has its own dedicated circuit). If you have no power to the fuse clip, the switch is bad or you have a broken wiring connection between switch and fusebox. Pretty well end of diagnosis there. Since you have the original torpedo fuse for the fan, lift the fusebox and look for burnt wiring behind Fuse 16.

Stack86’300sdl · #29 10-27-2019, 07:46 AM

Thanks for that response. I will check and change the fuse to the inline strap fuse type. I’ve been looking online for how to actually pull the fuse box. I obviously don’t want to screw anything else up, can you tell me how to remove the fuse panel? Also, is there anything else on the switch connection besides the blower? Anything else to check to rule out or to help make a positive determination that the switch is the culprit? Thanks again for the help.

Diseasel300 · #30 10-27-2019, 11:35 AM

The fuse box is held in by a few phillips head screws. Look between the fuses, you'll see them. Undo screws, lift up. Make sure the battery is disconnected first!

The blower has it's own dedicated contact on the ignition switch. If you get no power at all to the fuse for the blower, that contact has likely failed.