fan fuse keeps blowing - '87 300E - PeachParts Mercedes-Benz Forum

raysea390 · #1 06-10-2008, 08:07 AM

Its 100 degrees here and my fan keeps blowing a fuse, and hot air is coming out of the side and foot vents. My AC doesn't work and I had no intentions of fixing it.

The last month or so i have heard a flopping noise behind the dash like a vent flap opening and closing every second or so. Could this cause the fan fuse to blow and if so, is there a fix for this?

On a realted note, no matter the position of the climate controls, no air ever comes out of the center vents...is this because my AC doesn't work? If I get my AC fixed (might just need recharging) will air come out of those vents?

raysea390 · #2 06-11-2008, 08:41 AM

See my original post...has no-one had this problem before?

mbdoc · #3 06-11-2008, 08:48 AM

Is the blower motor fuse (30A) the one that is blowing? or is it fuse # 7 that blows?

raysea390 · #4 06-11-2008, 11:53 AM

its fuse # 7...I believe there's a whole bunch of other items on that fuse.

raysea390 · #5 06-11-2008, 02:44 PM

Wow - I just pulled out the card from the fuse box...on that one blown fuse is:

back-up lights
heating water valve
water pump (electric? auxiliary? disconnected a long time ago)
engine fan (electric? disconnected a long time ago)
heating system for washer jets
climate control system
relay aux. fan term 86
automatic transmission electrics
blower motor inside temperature sensor
AC compressor (AC hasn't worked since i bought the car last September)

I need to find out what's blowing that fuse pretty quickly...the heat in the car is unbearable enough but without that fuse theres a lot of things affected. Go any clues anyone?

JimFreeh · #6 06-11-2008, 02:56 PM

Looks like you are going to have to eliminate the items one by one.

Some are easy.

Check for a dead short before replacing fuse.

If no short, then start cycling each load, while checking for a short.

Remember to have key in #2 position when checking, since these are switched loads.

Jim

LUVMBDiesels · #7 06-11-2008, 03:02 PM

Does it blow regardless of where the CCU is set or only when the inside fans are operating? You might have a stuck 'blower motor inside temperature sensor'

I did on the SDL and it blew that fuse. On the W126 it is located on the passenger side kick panel directly under the glove box. Disconnect that and see it it helps...

BTW, a lot of WD40 and electric contact cleaner got mine running again

raysea390 · #8 06-11-2008, 03:03 PM

Jim...how do i check for a dead short? Presumably I replace the fuse and then what?

raysea390 · #9 06-11-2008, 03:08 PM

My blower fan runs all the time no matter what button I push...the 'off/on' button only shuts off the fan when i hold it in...when i let it go the fan starts up again. My fan speed buttons seem to work fine though. This is how the car was when i bought it.

I still think the problem has something to do with that flopping noise behind the dash somewhere...like a flap is cycling open and closed.

JimFreeh · #10 06-11-2008, 04:45 PM

Quote:

Originally Posted by raysea390

Jim...how do i check for a dead short? Presumably I replace the fuse and then what?

Dead short is where you ohm meter goes to zero resistance.
The flapping may be your recirc door.

In any event, your HVAC control unit sounds like it's flakey.
I've got a few laying around if you'd like to swap one out and see if it helps. I'm about 25 minutes south of downtown P-town.

Jim

raysea390 · #11 06-11-2008, 05:05 PM

If it is the recirc door flapping I wonder if that would cause the fuse to blow. I am going to replace the fuse (again) and see if the flapping goes away when i press the recirc button. Then I'm going to look for anything obvious wrong with all the other items on that fuse, plus check out that suggestion to remove the kick panel under the glove box to see if a fan is sticking.

I think the whole car is flakey...but I still love driving it, even when scorching hot air is coming out the vents in 100 degree weather!!! I'll let you know if I want to mess with the CC controls Jim...thanks!

JimFreeh · #12 06-11-2008, 05:10 PM

Quote:

Originally Posted by raysea390

If it is the recirc door flapping I wonder if that would cause the fuse to blow. I am going to replace the fuse (again) and see if the flapping goes away when i press the recirc button. Then I'm going to look for anything obvious wrong with all the other items on that fuse, plus check out that suggestion to remove the kick panel under the glove box to see if a fan is sticking.

I think the whole car is flakey...but I still love driving it, even when scorching hot air is coming out the vents in 100 degree weather!!! I'll let you know if I want to mess with the CC controls Jim...thanks!

Ummm, you've got to pull the wiper mechanism to check the blower....

Jim

raysea390 · #13 06-11-2008, 08:54 PM

Remove wiper motor to get to blower motor...I don't like the sound of that.

luvMBdiesles wrote that on his SDL it was a stuck blower motor inside temp sensor which is located on the passenger side kick panel directly under the glove box in a W126...its not that easy on a 300E is it?

May be looking for a buyer instead...

Arthur Dalton · #14 06-11-2008, 09:10 PM

Your problem is not in the blower. That is a different fuse. If the blower fuse was giving you a problem , then you would have to get to the blower.
Your problem is on the CONTROL side of the blower circuit..that is what fuse 7 protects.

LUVMBDiesels · #15 06-11-2008, 09:35 PM

That fuse does operate the small temp. sensor blower which is located under the glovebox in the W126. The main circulation blower runns off a different and much bigger fuse. In the W126 that bkower is also located under the glove box and can be removed in a few minutes.