Blower Not Working

[geraniumtr]

Folks, My DD 94 E320 with 272K miles. HVAC was working normally. Blower motor changed 2 years ago, regulator changed 6 months ago. Monday morning I have no blower on any setting of the PBU. Instead I'm getting heat from the defroster vents at all times. I had a spare strip fuse so I threw it in --no change. Also have a spare push button unit so I swapped it --again no change. I pulled the blower motor ---worked fine with battery voltage applied. I also happen to have a factory regulator as a spare since there was a K.A.E. in the car so I installed the genuine regulator---no change.
I got access to the 3 pin connector behind the brake booster. I'm getting battery voltage from each pin when grounded but no voltage from pins 1 and 3 when jumped which I read that I should have. Also getting battery voltage from the strip fuse when grounded but no voltage across the fuse.
Then yesterday the blower came alive and on a short drive worked normally. But this morning no blower, just heat from defrost vents.
Any help would be appreciated.

Regards,

Peter Weissman

 

[geraniumtr]

Folks, problem appears to be solved. Fuse # 7 in the main fuse box. Looked OK but it wasn't. New fuse did the trick.

I should have studied the fuse listing placard more carefully.

Regards,

Peter Weissman

 

[gerryvz]

Glad you fixed it !! So often it is the simple things rather than the complex things.

 

[DL2]

I am having difficulty with my blower fan as well on my ‘93 500e. It seems to run on low only. I have checked fuses and strip fuse. Pulled the motor and it bench runs perfectly. Replaced the resistor… twice thinking I may have a bad one. I’m not quite sure where to turn next. Any suggestions would be greatly appreciated!

 

[Jlaa]

I am having difficulty with my blower fan as well on my ‘93 500e. It seems to run on low only. I have checked fuses and strip fuse. Pulled the motor and it bench runs perfectly. Replaced the resistor… twice thinking I may have a bad one. I’m not quite sure where to turn next. Any suggestions would be greatly appreciated!

Have you tired a spare PBU yet?

 

[DL2]

Have you tired a spare PBU yet?

 

[DL2]

Haha! I don’t even know what a PBU is, so probably not! Please tell me more!

 

[gerryvz]

PBU - push-button unit. THe button controls in the dashboard.

 

[gsxr]

I am having difficulty with my blower fan as well on my ‘93 500e. It seems to run on low only. I have checked fuses and strip fuse. Pulled the motor and it bench runs perfectly. Replaced the resistor… twice thinking I may have a bad one. I’m not quite sure where to turn next. Any suggestions would be greatly appreciated!

The "resistor" is the speed regulator. If you replaced it with a new one and there was no change, it may be receiving an incorrect signal.

The signal is received by the PBU (explained above) but PBU failures that keep the fan at low speed only would be very, very unusual.

What brand regulator did you install, btw? IIRC, signal voltage should be +6v to make it run on high speed, may be ~1v at low speed.

 

[gerryvz]

It’s a pretty classic failure of the blower regulator to fail in one of two modes — either complete failure so the fan doesn’t work at all, or failure in one speed mode but no others.

For the earlier cars, you have the option of a Behr regulator I believe, or the $$$ MB unit. Facelift car owners like me only have the option of MB or KAE, which is a somewhat iffy Chinese made aftermarket brand.

 

[DL2]

Thank you. I am pretty certain I did not buy a Behr, certainly not a MB part. Should have asked about this sooner!! Thanks.

 

[Jlaa]

It’s a pretty classic failure of the blower regulator to fail in one of two modes — either complete failure so the fan doesn’t work at all, or failure in one speed mode but no others.

For the earlier cars, you have the option of a Behr regulator I believe, or the $$$ MB unit. Facelift car owners like me only have the option of MB or KAE, which is a somewhat iffy Chinese made aftermarket brand.

Thank you. I am pretty certain I did not buy a Behr, certainly not a MB part. Should have asked about this sooner!! Thanks.

If you have a prefacelift car and you want to save moolah, sometimes you can find ACM regulators (power transistors) that are actually re-stickered OEM Bosch/BEHR units.

OWNER - jlaa (500E & w210 E320) | Owners and Their Cars

Not Evos... NEEZ! That's, like, turning the knob to eleven. :gsxrock: Oof. Just now understanding what you were saying Dave. Jlaa... my deepest apologies... My E500Eguru epaulettes will surely be taken now! Sent from my iPhone using Tapatalk

www.500eboard.co

 

[DL2]

Thank you… yes it’s a ‘93. Thanks for the info!

 

[DL2]

So the fan is always running on low if the key is on… PBU? Also could PBU contacts need cleaning? This car sat for a number of years, I had to push very hard to activate the window switches when I first got the car.

 

[gsxr]

The fan runs on low when the key is on, unless the PBU is set to "O" (Off).

If the fan runs on low in "O" position, either the PBU or regulator may be faulty.

 

[DL2]

Thank you. I guess diagnosing just requires throwing parts at it until something works.

 

[geraniumtr]

DL2, I'm sure other members will chime in here. . . never a good idea to just throw parts at a problem. I recently had a blower issue so maybe this will help. Dumb question but did you check torpedo fuse # 7 with a multi meter or just visually ? A visual check is not definitive (BTDT).

There is a 3 pin connector behind the brake booster to be checked. For access pull off the drivers side weather stripping bottom of windshield and remove the plastic water drain. You'll see the connector under the cowl. Red wire is 12V , black is ground, yellow is the control to the blower regulator. Yellow voltage will vary based on fan speed selected on the push button unit. With ignition in 'on' position check with a meter. Carefully open top of pigtail to connect test leads ( don't let pins slide out). Put the PBU in any position but off and check for voltage.

I'm not a pro at electrical diagnosis but others may assist or search the internet. There is diagnostic help there too.

Regards,

Peter Weissman

 

[nocfn]

that 4 letter word: TEST!

 

[DL2]

Thank you, these are exactly the kinds of suggestions I have been seeking. I hate just throwing parts at a problem. The 3-pin connector is new information to me. Thanks again!

 

[gerryvz]

There are only a very few things that can be the cause of a blower motor not working, or not working properly.

With a motor that is only working at one speed, it is very much the most likely thing that it will be the regulator. PBUs don't fail that often, and obviously fuses and such are working seeing that it is running in low speed mode. I recommend changing out the regulator. Since you have a pre-facelift car, you have a couple of options for quality parts. Or, you could try a used one.