116 blower failure diagnostics - PeachParts Mercedes-Benz Forum

kerry · #1 12-17-2008, 08:30 PM

My 79 SD blower has quit. Fuses are ok. Hitting the motor does nothing. Vacuum portions of the servo are working ok since I can hear the flaps moving. Blower was cutting in and out intermittently before it quit altogether. I plan to check the voltage at the wires to the motor. If I have voltage there, I'll pull the motor. If I don't have voltage at the blower, what's the next step?

kerry · #2 12-18-2008, 11:08 AM

Ok, whoever has cursed at the 116 blower motor, chime in. The wires are way on the right side of the motor and so far I haven't been able to trace them any further to get a meter on them to see if they are getting voltage. Damn, that area is tight! Did the people who removed the motor first remove the plastic ductwork to get access to the mounting screws? Did you pull the kick panel from under the glovebox? This is a more unpleasant job than I anticipated. One of the mounting screws for the blower is readily accessible but the other 2 are buried behind the ductwork.
Is the blower power fed from the amplifier? Can I check at the amplifier to see if it is sending voltage to the blower? The amplifier is easily accessible but I don't know what wires are what at the amplifier. Initially I was hoping it was the brushes in the motor but now I'm wishing it's the amplifier.

Graplr · #3 12-18-2008, 11:17 AM

Kerry,
I have the entire blower unit that I pulled from my 116 (duct work, blower, amp and all still assembled). I didn't drive it that long, but I do remember the blower working on hi and lo.

I can't help with info on how to troubleshoot as I just dissasembled mine.

But if you find that you need parts, pm me.
-Ryan

kerry · #4 12-18-2008, 11:23 AM

Quote:

Originally Posted by Graplr

Kerry,
I have the entire blower unit that I pulled from my 116 (duct work, blower, amp and all still assembled). I didn't drive it that long, but I do remember the blower working on hi and lo.

I can't help with info on how to troubleshoot as I just dissasembled mine.

But if you find that you need parts, pm me.
-Ryan

Ryan:
Thanks. Once I figure out what's going on, I may be in touch. Did you pull off the kick panels to disassemble yours?

Graplr · #5 12-18-2008, 11:36 AM

Quote:

Originally Posted by kerry

Ryan:
Did you pull off the kick panels to disassemble yours?

I think I took the entire dash out before I even got around to pulling the blower so I doubt you want to go that route.

I just pulled my 126's blower to examine the brushes and know I had to take off the kick panel for that. I don't specifically recall how the 116s kick panels are but I would imagine you already did that to gain access to the blower, didn't you??

kerry · #6 12-18-2008, 11:53 AM

More information: I was able to stick my meter probe into the red wire going to the blower. I have .02 volts on defrost and 2.5 volts on both hi and lo settings. So it's not getting enough voltage. Anyone know why this might be happening? I probed the wires at the amplifier. I don't know what those wires do but some showed system voltage of 12+ and others were in the range of 5 volts or 7 volts. Anyone know if a bad amplifier results in low voltage to the blower motor?
I took out the amplifier and there are a few connections on the board that are a darkish brown. Does this indicate overheating and failure? I have no idea how to test the amplifier beyond looking at it.

kerry · #7 12-18-2008, 12:10 PM

OK, more info. I disconnected my pointy probe from the meter, fed 12 volts to it and stuck it into the red wire at the motor. Blower motor ran fine. So--the problem is elsewhere. I assume there are three possible general causes. Either the servo, the push button unit or the amplifier. Anyone know how to narrow down these possible sources of the problem or suggest another possible source?

Graplr · #8 12-18-2008, 01:02 PM

On the 116, isn't the push button unit just a plate and have no circuit boards and such in it? Isn't everything in the servo?

I'm not 100% sure (I believe it did as I recall my blower changing speeds)my amp works, but if you want to pay for shipping, I can send it out to you. You can try it and if it works and solves your problem you can keep it and pay me then. If it doesn't help you, just ship it back.

I also have the servo from the 116, but I have no clue as to the state of it. I know the heat worked but the a/c wasn't charged so I could test that. I can send that as well although that probably isn't an easy swap out.

derburger · #9 12-18-2008, 01:38 PM

The blower motor has a vacuum switch on it. If this switch doesn't reach sufficient vacuum (i.e there is a leak in the vacuum system) then the blower will not turn on.

IIRC, the amplifier receives voltage from a potentiometer in the thumbwheel, which is sent back to the servo from the amp to open/close coolant pipes and control.

I believe your problem is vacuum related, since it seems the ACC electrical system is in order.

In my case, there was a leaking diaphragm in my system, which lowered the vacuum in the ACC system so the vacuum switch on the blower wouldn't flip on.

I would test your vacuum actuators in the ACC system with a mityvac, since if one ruptures, nothing in the ACC will work. You have defrost, center vents, fresh air/recirc flap, legroom flaps to test, George murphy sells the replacement rubber for inside them, if they are ruptured. If you find a leaky one with your mityvac, plugging the line with a golf tee should make your blower work again while you wait for the replacement diaphragm. Replacement diaphragms are around $5, you take apart the pod and replace the rubber inside.

kerry · #10 12-18-2008, 01:39 PM

My servo was replaced in the not too distant past so it's not likely that it's the servo. The servo is responding to vacuum change commands and it is passing heat through the heater core. The only problem seems to be lack of proper voltage to the blower motor. I don't know what controls the voltage to the blower. It seems odd that the voltage is so out of wack. I'd anticipated a complete failure somewhere, not just way low voltage.
Anyone know what voltage I should be getting at the blower at various speeds?

Your amplifier may be the next best and simplest testing sequence? Do you have a paypal account? How much do you want for it? Any idea on shipping?

kerry · #11 12-18-2008, 01:44 PM

Quote:

Originally Posted by derburger

The blower motor has a vacuum switch on it. If this switch doesn't reach sufficient vacuum (i.e there is a leak in the vacuum system) then the blower will not turn on.

IIRC, the amplifier receives voltage from a potentiometer in the thumbwheel, which is sent back to the servo from the amp to open/close coolant pipes and control.

I believe your problem is vacuum related, since it seems the ACC electrical system is in order.

In my case, there was a leaking diaphragm in my system, which lowered the vacuum in the ACC system so the vacuum switch on the blower wouldn't flip on.

I would test your vacuum actuators in the ACC system with a mityvac, since if one ruptures, nothing in the ACC will work. You have defrost, center vents, fresh air/recirc flap, legroom flaps to test, George murphy sells the replacement rubber for inside them, if they are ruptured. If you find a leaky one with your mityvac, plugging the line with a golf tee should make your blower work again while you wait for the replacement diaphragm. Replacement diaphragms are around $5, you take apart the pod and replace the rubber inside.

Do you know where that vacuum switch is so I can try jumping it? There's no evidence of vacuum problems anywhere. Car shuts off fine, doors open and close fine. I can hear the flaps operating in the climate control system. I suppose it's possible that there's a leak in the climate control system that is not manifesting anywhere else.
How does that vacuum switch work? Would the lack of function in that switch reduce voltage like I'm seeing?

Graplr · #12 12-18-2008, 01:57 PM

PM sent.

kerry · #13 12-18-2008, 07:03 PM

I found the main blower vacuum control switch (it's above the blower and green colored) and jumped it. Made no difference. I am now concluding that since the voltages at the blower are very low and the purpose of the 'amplifier' is to amplify the signals from the temperature control sensors, that the amplifier has failed. Once I get the amplifier from Graplr I can test the hypothesis.

By the way, even though I posted a separate thread on this topic, if people need the service manual for the servo system, here it is. The fact that it's a Chrysler Imperial site, tells you that the relationship between MB and Chrysler goes back a long ways.

http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm

PanzerSD · #14 12-19-2008, 12:30 AM

Quote:

Originally Posted by kerry

My 79 SD blower has quit. Fuses are ok. Hitting the motor does nothing. Vacuum portions of the servo are working ok since I can hear the flaps moving. Blower was cutting in and out intermittently before it quit altogether. I plan to check the voltage at the wires to the motor. If I have voltage there, I'll pull the motor. If I don't have voltage at the blower, what's the next step?

was it making any kind of noise before it quit? I had a blower that quit, turns out one of the magnets inside the case fell apart and jammed the works.

it's probably easier for you to remove the whole fan housing, then there's less space requirements to pull it back.

a new motor is some heavy $$ I couldn't find a good replacement for less than $200 here, so I fanagled a nissan motor in there. everything was good except the screw hole locations were in the wrong diameter, so I cut the flange off the old motor and welded it around the new motor and voila!

my blower story...

kerry · #15 12-24-2008, 04:00 PM

It was the amplifier. Blower is now blowing. Thanks to Ryan (Graplr) for supplying me with a replacement.