W126 PBU relays clicking inside - corresponds with idle speed
 

I am uploading the video as I type this. The video shows and explains what is happening. Keep in mind, shutting the car off and turning the key to KOEO does not produce the same symptom.

JamesDean, are you out there? I would like to hear what you think of this odd issue.

I am always out there! Lol.

I've heard this before. I can't remember more specifics though. My first thought is a cold solder joint. Just because its a ProGramma rebuilt does not mean they did a good job on the soldering. I've seen a few rebuilt units from them (cruise) and they did only what was necessary to get the unit functional. They did not actually do all the joints or replace component that I do.

My second thought is a voltage issue. Monitor your voltage as you vary the engine RPM. You might be sending the PBU intermittent signals.

My third thought would be something in the temperature regulator unit but I am trying to remember the schematics. I dont really remember the TRU connecting back into the PBU for relay connectivity. I think PBU controls all flowed into the TRU and nothing in the reverse direction.

My guy says cold solder joints. I would not let that run like that for too long. You are right it could potentially wear out the relays but also cause current draw on the traces and end up damaging something else. I can't say with certainty though.

There appears to be some kind of common trend on these W126 units. I've seen at least three that needed or had a trace blow out and be repaired in the same sense that this unit (in the photo album)

W126 300SD (1983) Climate Control - Push Button Unit PS - Album on Imgur

I'd be happy to go through your unit if you'd like. Might be prudent to have the temperature regulator re-done too since the pbu will be out.. Drop me an email--JamesDean59@gmail.com--if you're interested.

Mine did some clicking like that at one time. When I opened it up, the solder connections between the boards had hair-line cracks. Cleaned and re-soldered with no further issues. Any movement,affecting the center console area, can cause the hair-line crack to be intermittent.

Even a rebuilt unit could have been damaged in return shipment.

Thanks for the suggestions, guys. It looks like I have some testing to do. I did notice that before the car heats up, the PBU does not make the sounds. I can attribute that to the 40C lockout switch, I assume. If it is not an obvious case of alternator or battery issues, I think I will go through the PBU and touch up the solder joints and see where we are after that. I also have spare PBUs, TRUs, and fan relays.

I am pleased to announce that I have found the problem and it is a simple fix.