Blower motor runs for 20 seconds then shuts off
 

Have a 94 e320 and the blower motor runs great for 20 seconds then shuts off and won't run again until the car has been off for 10 to 15 minutes. I'm thinking the motor is OK but maybe some type of relay is tripping. Any idea on where to start on this. ?

Make sure the blower fuse has power with the key on.

If that is OK, then most likely an electronic blower regulator issue.

where is the electronic blower regulator located? Is it in the blower housing? I just bought the car and I fortunately have a donor car of the same year and model due to getting hit by a high speed deer.

Fuse is ok, I have a donor car with good blower and blower regulator. Switched those with the current e320 and the blower will run with key on engine not running. With engine running blower goes from high to very slow after 20 to 30 seconds. If you turn off the blower switch for 5 minutes and turn it back on it will run for 20 to 30 seconds. Blower is on high, not auto

240diowa, not sure if a 1994 E320 has a 30-amp strip fuse for the blower motor, but if it does closely examine the strip fuse for a hairline crack across the fuse. That may be your problem.

Thanks to this thread I got my blower motor working again. I too found a hairline crack across the middle, just as I did for the rollbar fuse a few years ago. What I find curious is that these weren't blown (or melted) from shorts. They seem to be mechanical breaks. I'm no stranger to metal fractures, so I'm guessing it's from thermal fatigue. They are made of zinc and are held fast at each end. These strip fuses merit a redesign. Probably something with a bend in it, like most modern automotive fuses.

It has been suggested elsewhere in this forum that good preventative care would include changing all fuses on the older cars. I am sure mine has 26 year old fuses.

Perhaps. Though the failure mode of the strip fuse is different from the bullet fuse, the idea has merit.