SD Blower Controller - PeachParts Mercedes-Benz Forum

Brian Carlton · #1 11-19-2005, 06:44 PM

The SD has no functioning blower.

It has power on fuse #11 but there is no power at the blower. The blower runs fine when 12V is applied directly.

Anyone know where the blower controller is on the SD?

Anything else to check?

Johnhef · #2 11-19-2005, 07:09 PM

blower regulator controller up behind the passenger lower dash, the black box.

Brian Carlton · #3 11-19-2005, 07:37 PM

Quote:

Originally Posted by Johnhef

blower regulator controller up behind the passenger lower dash, the black box.

John, there is a black box attached to the back of the kick panel. It appears to be related to the sound system at some point in the past since it has a type of coax connector.

I presume the regulator must be attached directly to the firewall in some fashion. What size would it be???

Hit Man X · #4 11-19-2005, 08:04 PM

For some reason I believe the pre 86s to have a similar relay to the Klima of the '86+. I could have sworn I've seen it down there... unless it's in the fuse box

Pete Burton · #5 11-20-2005, 12:06 AM

Brian, did you check the cold engine lockout? It's next to the EGR temp switch. The wire to that switch needs to see ground or the blower won't work.

Brian Carlton · #6 11-20-2005, 01:26 AM

Quote:

Originally Posted by Pete Burton

Brian, did you check the cold engine lockout? It's next to the EGR temp switch. The wire to that switch needs to see ground or the blower won't work.

I definitely need to do that, Pete.

Can you confirm that the blower won't work on both HI and LO, in addition to AUTO? Hattie mentioned that the blower will function on HI and LO, independent of the temp switch, but I can't remember if this was true on the SD.

Thanks for the heads up. Especially since that switch was involved in the removal of the head.

Johnhef · #7 11-20-2005, 02:53 AM

I'll find you a part number or a picture tomorrow. I just took apart an 84 SD that used the same box as the 123's did. My 123's only worked on high and low, but only because someone had rewired the regulator box to work.

Brian Carlton · #8 11-20-2005, 09:17 AM

Quote:

Originally Posted by Johnhef

I'll find you a part number or a picture tomorrow. I just took apart an 84 SD that used the same box as the 123's did. My 123's only worked on high and low, but only because someone had rewired the regulator box to work.

Thanks. Maybe I'll get lucky and the ground switch will be the culprit. Seems very odd that the blower dies after a 5 month hiatus.

Johnhef · #9 11-20-2005, 10:03 AM

as promised:

Brian Carlton · #10 11-20-2005, 10:20 AM

Quote:

Originally Posted by Johnhef

as promised:

Fantastic.

Thanks.

#11 11-20-2005, 04:52 PM

Quote:

Originally Posted by Brian Carlton

Fantastic.

Thanks.

Now its time to go on an egg hunt

Defintily check that sensor first...but you SHOULD be able to put it into defrost mode (or the next one over from the left) and put the fan on max and have it come on.

If it still doesn't come on...I guess you get to track down the black box.

That sensor is expensive...mine was non working when I got it and now bypassed.

Brian Carlton · #12 11-20-2005, 05:50 PM

Egg hunt completed.

Problem remains.

I found the controller and I did confirm that the controller has power from the fuse box. I also could see some grounds appear and disappear on certain pins when the high or low fan switch was pressed. No amount of fiddling would get the blower to work.

Now, here is where it gets interesting.

I had purchased a complete heater box assembly with all actuators from Houston European. Got such a good deal that I couldn't pass it up. Low and behold, it has the controller attached. So, I figure I'm all set.

I swap controllers and nothing.

The second controller does the exact same thing as the first.

So, what's the chance that I have two bad controllers?

I have a suspicion that something else is the problem, but without a schematic of that controller, I've got no way to check it.

Anyone find any schematic of all those pins. The online manual only shows the 12V input.

I might just see if I can swap these two controllers into a known vehicle. They might fit the SDL. But, it will have to wait a couple of weeks since I'll be away.

sixto · #13 11-20-2005, 11:58 PM

The CD manual shows pin 3, 4, 5, 6, 7 or 11 is powered depending on which blower speed is selected. That pin sends power through a stack of however many resistors is necessary to reduce blower speed. If there is +12V at pin 6 on high and +12V at pin 11 (might be easier to check at pin 5 of the resistor pack) on low then I imagine you can acquit the blower controller. At that point I imagine the resistor between pins 2 and 4 in the resistor pack is open. I'd start at the resistor pack and work back to the blower controller.

Sixto
87 300SDL

Brian Carlton · #14 11-21-2005, 12:41 AM

Quote:

Originally Posted by sixto

The CD manual shows pin 3, 4, 5, 6, 7 or 11 is powered depending on which blower speed is selected. That pin sends power through a stack of however many resistors is necessary to reduce blower speed. If there is +12V at pin 6 on high and +12V at pin 11 (might be easier to check at pin 5 of the resistor pack) on low then I imagine you can acquit the blower controller. At that point I imagine the resistor between pins 2 and 4 in the resistor pack is open. I'd start at the resistor pack and work back to the blower controller.

Sixto
87 300SDL

Thanks Sixto.

Any idea where the resistor pack is on the W126? I seem to remember a toaster looking cube on the passenger fenderwell of the W123, but, I haven't noticed the pack on these two?

I suspect that you are right on the money with that diagnosis. The chance of two different controllers being non-functional is just about nil.

Can those coils be replaced, or do you need a completely new unit?

Pete Burton · #15 11-21-2005, 08:42 AM

Brian, the resistor pack is below the brake booster.