I have read many of the threads on the PBU, BLower, Fuse 7.....

I thought that the issue was the PBU because it would work every now and then, when warm. I would have to wait for the car to warm up and then cycle the key from on to off then back on, usually while driving, and the heater system would then start working. The blower would pump out hot air and when I turned it to cold it would cool down, no A/C it was disconnected by the previous owner. So I finally got my hands on a newer PBU, plugged it in last night and nothing . I can hear the blower when outside the car, it is very quite and blows just a little bit of air, if I change the temperature it adjusts the heat but still only a little bit of air. When I turn it to full on no change in air speed.

Does anyone have any idea where I should start?

I also hear a clicking noise if I turn it to all the way cold, once again no a/c and I can see on the air recirculating button that the red light is flashing in tune to the noise that is heard under the glove box.


Thank you for the help

What car? Year? It matters when diagnosing this type of problem so you know where to look

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Sorry, it is a 1987 300td wagon

You shouldn't be seeing the recirc button flashing. Was it doing that with the previous CCU?

I'd suspect your original CCU has bad solder joints on the switches for the pushbuttons and possibly for the ribbon cable for the fan speed switch. The fan in my SDL would randomly drop out or get stuck in low speed, then finally died completely. The solder connections on the CCU board were the problem. Re-soldered and has never given an issue since.

Other things to check:
- In-line fuse to blower module. 1987 could have the fuse outside the fuse box. If it's like the 126, it'll be a 30A strip fuse like the defroster uses. They can crack.
- Blower control module (porcupine). When they fail they can cause strange issues.
- Motor brushes. If worn down, they can cause problems with lack of torque in the motor
- Ignition switch. The blower has it's own set of contacts in the ignition switch. If you leave it in one position and wiggle it a little bit and the blower comes on or speeds up, you likely have an issue there.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Ok, a bit of an update.

I was taking out the new PBU and when I disconnected only one side(right side when looking at the dash) the blower motor kicked in at full speed. So I know that the blower is getting power, that confirms that the fuses are working(30A as well) and the blower motor is working and bushings are not shot. I also unplugged the three-prong Red, Yellow and black connection behind the brake cylinder, when I did this the little bit of air that was coming out stopped completely. The center prong has 11.85V going to it. Any other suggestions?

I found that when I plug the Right side in on the PBU pin number 12 is the one that cuts off the blower motor. Not sure if that helps. Also the new PBU part number is 124 830 24 85. I can see that it is interchangeable with 124 830 22 85 but not 124 830 18 85. I am not 100% sure what part came out of the car because there are no markings on it.

Thanks for the help

Does this sound like a blower regulator problem?

Sounds like the new Pushbutton Controller is part of the problem, now. Your year/model calls for the 124 830 18 85 88.

With the original problem, was the blower working but just no heat? If so, it may be the Heater Control Valve is hanging up.

1987 Mercedes-Benz 300TD Base Wagon - Heater System - Page 1

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

With the original, the heater was blowing hot air when the system would work. But I would have to wait a bit for the car to warm up and then cycle the key on/off/on for the system to kick in. Once it kicked in heat and cold would work. There is power going to the Heater Control Valve as well. And I did hear it moving.

There is a coolant temp sensor in the system that cuts the blower motor until it reaches a certain temp. Is this what you're seeing?

If that was the case why would I have to turn the key to get it going again? But it could be the case. Where is the temp sensor and how do I test that? Oh, that is on the return housing for the coolant. How can I test that it is working?

If you stop the key and wait before turning it again, it's possible that the sensor in the head is warming up enough to close and allow heat. There is a delay from a cold engine, but it shouldn't be more than a couple minutes. As soon as the engine begins to warm up, it should start blowing heat. It certainly sounds like your current problem is the CCU. I'd put the original back in and troubleshoot the heating issue. Try setting the temp wheel to max cold and see if the fan turns on. If it does, you know the delay is probably due to the temperature sensor in the head.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

I do not think it is a heat issue because when the blower motor turns on it blows hot or cold. It is getting the blower motor to turn on that seems to be the problem. Sometimes when the car is warm turning the key on and off does nothing, blower motor stays off. Also when driving, as the car is warming up, there is heat blowing out of the defrost vents, this stops only when the blower motor starts running ie. turning the key on and off, but like i said that doesn't always work.

Someone mentioned that it might be a motor regulator issue because with the new PBU(CCU?) installed there is a little bit of air that is blowing out of the defrost vents and i can control the temperature of that air with the PBU.

Thanks again guys

It's starting to sound like it may be just the blower motor starting to go out. Turning the key off/on probably just "unlocks" it when it hangs up. Sometimes connecting the blower directly to a 12V source can even be deceiving.

Have you pulled the blower motor and just inspected the armature and brushes? I'm not sure how much of a job it is on your car (mine comes out in about 15 min. or less) but it should be less trouble than pulling Pushbutton Controllers.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

I have not pulled the blower. I just ordered a new blower regulator and will open it all up when that arrives. If it is the blower then I will know then.