I have a 1987 300D. The old blower motor stopped. I pulled it out and yep, it's shot. I bought a replacement and plugged it in before a full re-assembly and it didn't work. I checked the main fuse panel and that was ok. I looked at a friends '87 300D and he showed me the fuse link by the strut tower, however my 300D doesn't have a fuse link anywhere. Any thoughts?
I tried a replacement blower regulator, still no luck getting the blower to work. Are there any relays to search and test?

If you stand facing the rear of the car, the compartment (about 4" X 6") directly aft of the fuse compartment holds the relay for the fan. I think there are eleven relays in there but I don't recall which one is in the fan circuit. Someone else will surely jump-in here with the answer.

Thanks. With winter coming I need the blower to work.

The box you mentioned. It's the one with the lid held in place by screws?

Correct.

Good Luck!

Check back-in after a while. You'll have some further help, no doubt.

Would anyone know why a new motor would not function when hooked up to an external 12V power source? I wanted to make sure the new part functioned for installing the "squirrel cages" and re-installing the motor into the car.

Should work fine with 12v applied, otherwise a bad blower motor.

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Gone to the dark side

- Jeff

I finally got the new motor to work with an external source.

Still no luck diagnosing why the motor won't work when connected to the regulator.

I mentioned earlier I couldn't find the 30 amp fuse link by the strut tower. I found what appears to be a fuse link behind the drivers side headlight. Anyone with any thoughts if this could be my missing blower motor fuse link?

First - I assume you mean the heater/AC fan motor, located under the windshield wiper. Right? In that case:

Only the late 1987 300D's have the external 30A strip fuse. Early models (like mine, built in May 1986) still have the 25A fuse in the fuse box. Yours probably does too. Check that first. Cars after a certain date (late '86, early '87) all have the external fuse, all the way to 1995. But 1986 and early '87 models do not.

There is NOT a relay for the climate control blower. It connects directly to the speed controller, aka "porcupine", named such due to the way the finned heat sink appears. That is located underneath the fan itself. If it was working OK before, it's not likely that it suddenly failed.

There are 2 relays behind the fuse box, but they are for the fan in front of the radiator, not the HVAC blower fan. There is no fusible link behind the driver's headlight, but there is a large ceramic resistor there, which is for the radiator fan "low speed" setting. That's probably what you're looking at.

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Dave
Boise, ID
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Thanks for the info. Yes, I'm troubleshooting the A/C, heater blower motor. I tried a salvaged motor regulator (porcupine) to no avail. All fuses in the panel are okay? The original motor failed due to worn out bearings. If fuses and regulator check out, is my next suspect the climate control unit?

One last item to check... after you start the car, turn the ignition key back gently - not enough to shut the car off. When the switch behind the key wears, it can kill power to the blower motor. I had this problem on my car, and it took me forever to diagnose the cause! For a while I just fiddled with the key to make the blower work, but after a couple of years I finally replaced the switch (which is a real PITA job.)

If that's not it... check for voltage from the 3-wire connector located approximately behind the brake booster, under the windshield drip tray. That leads to the porcupine. I'd also REMOVE the fuse and clean the sockets, not just trust a visual inspection.

How do I check the voltage at the 3-wire connector, i.e. red to a post and black to ground? What readings should I get at each post?

You said the last item to check is the ignition switch? Is that to say the climate control unit would not be a suspect?

Again, thanks for the info!

1) Check the ignition switch first. That is the easiest item to test.

2) Check for +12v at one of the connectors behind the booster. If there's no voltage, that's probably why it's not working.

3) Have you physically pulled the fuse yet?

4) Wouldn't hurt to unplug the aux heater pump below the washer fluid reservoir... these can short out, causing problems. Or set to max heat and see if it runs. I doubt this is the problem either, but it's worth a shot.

5) Last item would be the pushbutton unit... could be the problem, but I doubt it.

Yes, I have pulled the fuse and replaced with a new one. I'll check the posts in the connector by the booster and ignition switch Friday after work. I hate when work gets in the way of important things... Thanks for he advice!

Stay tuned...

On the previous mention of fuse locations on late/early '87 cars, one of my '87s was built 07/86, and both have the plastic holder between the left strut tower and the hood alarm switch. Is there truly another location for this fuse?

__________________

Gone to the dark side

- Jeff

Yup. All 1986 model year cars, and 1987's built before VIN A292112 (sedan) or F023505 (wagon), don't have the external holder with 30A strip fuse. Those early cars use a normal 25A fuse inside the fuse box. You'll even find a blank space at number 12 where that fuse normally would be. MB re-routed the circuit externally, but didn't use the old space for anything else. It's documented in the ETM,page 102/103.