So I am still having issues with the heat.

I just received the new blower motor regulator and I tested it with both the old and new PBU. It didn't change anything.

I did a short video that I posted on youtube here. https://youtu.be/55VRBFSrry0

Any new suggestions would be helpful.

Thank you

I'd suggest getting the correct PBU and trying again. The original clearly has some sort of problem, the replacement with different part number doesn't appear to be compatible with your car, or it too has some sort of issue. The 124 like the 126 had a change in the late 80s or early 90s where some discrete functions got moved to the PBU, so there may be some wiring incompatibilities if the new PBU is from a newer car.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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

Hey Diseasel300

Thanks for the idea. Do you think that the ignition switch could also be the problem because I have to play around with the key to get the system to work? I was thinking of replacing the ignition switch and get a new PBU.

What about the heater control valve? Does it usually make a bit of noise? I assume that it would not blow hot air at all if it didn't work.

Thanks

If wiggling the ignition switch has ANY bearing on whether or not the blower runs, replace it. The ignition switch has a dedicated contact for the blower and it does wear out. Wiggling the key should have no bearing on whether the blower runs or not.

The heater control valve does make a clunking noise when it engages. It's a solenoid after all. It shouldn't be sitting there clicking like you have in your video though. That is a function of the PBU doing something it shouldn't. The PBU should be opening and closing the valve according to the temperature of the heater core and the sensed temperature of the cabin. Repeatedly clicking on and off like in your video is not normal behavior, especially with the engine off like that. If it were calling for heat, the valve would be disengaged, if it were not calling for heat, it would be engaged (energized to close).

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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

Ok ignition switch will be changed. I should have thought about changing that a while ago.

And I just ordered a new PBU. I'll update once I receive the parts.

Thanks