87 300D heater fan falure - PeachParts Mercedes-Benz Forum

reiraj · #1 10-20-2009, 11:01 PM

The fan suddenly lost speed control with semiconductor smoke, then runs at slow speed, even when dash controls disconnected. Is the problem located at the fan, and must the dash be dismantled to do so? The heat control quit working also with removal/replacement of climate module behind the battery.

babymog · #2 10-21-2009, 10:55 PM

The blower and speed control are beneath the wiper assembly, which must all be removed.

The 3-pin plug above/behind the brake booster feeds the blower speed control, 12v/variable/ground. If there is 12v / / gnd, check the voltage on the center pin. If no voltage, and the fan is running, you have a bad speed controller "porcupine".

a2t · #3 10-21-2009, 11:28 PM

mine did same thing. fan motor and resistor needed. you can either keep the squirrel cages or just buy a new unit complete with new squirrel cages on it. if you swap your cages onto new motor, it will take a while to line them up. the clearance between cages and shrouding is about .050" per side, good luck. took me about 2hrs to line it up right.

blower motor is down below the monowiper. theres a thread right now on how to remove the monowiper, its not too bad. few hrs job. you will marvel at size of resistor down there, looks like something out of a nuclear warhead. hell it might be... oh i guess technical term for it is "porcupine"

oh yeah, take the chance to clean the evaporator. you will likely find 10 lbs of crud in it. now my blows like a hurricane, i love it.

Graplr · #4 10-22-2009, 12:43 PM

I'm not sure if the 126 blower will work, but I pulled a blower and resistor out of a 87 420 SEL and a 89 300 SE at the pick n pull last week. If you want to buy either one, PM me.

reiraj · #5 10-23-2009, 01:50 PM

Thanks everyone!! Being an EE I figured Merz eng's did something like this. Haven't been able to find docs in any public libraries on this car. The heat control appears to be a sticky valve in front of the battery. Each time I fiddle with the wire connector heat comes back for a while and then quits. I'm told there's a cheap replacement kit, but haven't found one at the local auto parts.

reiraj · #6 10-24-2009, 05:28 PM

OK I checked the fan out. There was voltage on all three pins. I removed the fan connector and applied battery to the red & black pins. It ran at slow speed. Shorting the yellow wire to black stopped the fan, while shorting it to red made it run full speed.

The wires in the harnesses going to the CCU in the dash are not the same gauge as the yellow speed wire in the fan cable. Is there an intermediate control somewhere else, or is the problem in the CCU? Aggravation.

C Sean Watts · #7 10-24-2009, 06:05 PM

Quote:

Originally Posted by reiraj

The fan suddenly lost speed control with semiconductor smoke,

I know I often lose speed control when I smoke semiconductors....

Ditto babymog. Go to 'fastlane' above (in 'buy parts') and search 'blower motor resistor.' There's also another thread going about this.

When the resistor goes it can fail in three (generally) modes - NO fan what so ever, fan becomes possessed and runs at random speeds or it will only run at minimum speed.

C Sean Watts · #8 10-24-2009, 06:11 PM

Quote:

Originally Posted by a2t

oh yeah, take the chance to clean the evaporator. you will likely find 10 lbs of crud in it. now my blows like a hurricane

I did this earlier this year in the wife's gasser, I went through the troubleshoot and got to the 'jump power the blower' and I got the 10 lbs of crud in my face!

babymog · #9 10-24-2009, 06:19 PM

Where are you located? I have a used one if you want to go that route.

reiraj · #10 10-24-2009, 09:57 PM

I traced the fan speed (yellow) wire from under the hood to the CCU plug. It's pin 12 on the driver side connector. I tried the same gnd & 12V short and the fan did as earlier today. Next thing I'm going to try is a rheostat to see if I can get full control at the CCU plug. I've resoldered every last blinkin pad on the circuit boards and checked all the diodes and power resistors. I'm not convinced the CCU is working properly at the moment.

I'm in KC MO. I'm hoping I can do a work around for the winter. Inspecting the wiper assembly it looks like a nightmare to get apart. But it doesn't hurt to have a spare fan for this baby. Is the seal in the heater control valve a dealer only item? That's wore out.

sixto · #11 10-25-2009, 03:04 PM

If the blower controller/porcupine is bad, there is no getting power to the blower motor. Here are the steps to getting to the blower motor and the controller that sits beneath it -

http://www.peachparts.com/Wikka/W124BlowerMotor

If there's a pick-n-pull yard in your area, now is the time to go. Lots of cash for clunkers cars in fine shape are making their way to the yards. You can practice removing the wiper assembly on those cars before breaking brittle plastic parts in your car. Then you have a source for all the parts you break in your car

Note that 94-95 cars have a different air box. The blower motor and regulator should work in your car but assembly and disassembly is not exactly the same.

I don't know if monovalve kits are available for the W124. I don't see them listed, only complete monovalves. You'll have to check the EPC or the dealer if seals and repair parts are available. Note the monovalve is open without power and closes with power. It has something of a PWM function to regulate temperature. If you want full heat to see you through the winter, just remove the electrical connector. You might get less than full heat when moving if the monovalve has an internal leak. If so, bridge the input and output hoses for full flow to the heater core. There's an auxiliary circulation pump under the washer fluid reservoir for better coolant flow at low engine speeds. It might impede flow if it's not active.

Sixto
87 300D

babymog · #12 10-25-2009, 07:19 PM

Is it a monovalve in the 124? I was under the impression that it was just on when calling for heat and the airbox was a VAV system.

sixto · #13 10-25-2009, 08:23 PM

Good point. I call it monovalve out of habit. It does revert to full heat without power like an older monovalve.

Sixto
87 300D

Jeremy5848 · #14 10-25-2009, 08:35 PM

The 124 and 123 monovalves are very similar in that no power = full heat in both. A rebuild kit (now NLA) used to be available for the 123 monovalve but never was offered for the 124 version. The only option is to replace. Since they are expensive, I would try getting one or two out of a junkyard, you might get lucky and find a good one. A junkyard "water valve" would probably be priced at $10 or less.

reiraj · #15 10-26-2009, 07:29 PM

Finally finished checking the system. The valve plunger/shaft were scum coated, and the shaft seal is worn. I cleaned the scum off, checked operation, and then put an O ring below and above the seal with a little gasket cement, squished it tight and let sit several hours. Today the valve was cycling after it reached temp and seemed to follow the CCU commands by temp setting. The problem is coolant gets into the coil chamber and prevents the plunger from moving back up once its turned off.

The fan however will not adjust speed with a variable voltage on the yellow wire, so I know the "porcupine" is damaged.

Babymob, I believe I will buy that fan off you if it fits. I just don't know how I can replace it in this cold weather. It looks like it will take a couple of days. I couldn't figure out how the wiper arm comes off.