This is about my '84 Euro 500SEL. When I purchased it some months ago, the A/C wasn't blowing at all. Not that it wasn't cold, but no air was coming out of the vents. Same goes for the heater. So, naturally, I thought the blower motor was the problem. Before I even started diagnosing the issue, I had the opportunity to purchase a used blower motor for a very good price of $20. So I did. A few days ago, I removed the old blower motor. I tested it by connecting it to my car battery and the thing blew strong! So it was working. I connected a voltmeter to the power connection to the blower motor and there was no voltage flowing to it. At that point I started suspecting the push button control unit (PBCU). Is there another step I should take in the diagnosis before I decide to replace the PBCU? Some additional info: (1) the current PBCU was actually a used one that the previous owner used to replace the original one in 2002 (just 15,000 miles ago) when the original one stopped working (2) I already replaced the fuse (3) at night, all the buttons on the car light up except the buttons on the PBCU.

Any help would be appreciated. I did several searches but most results deal with units that work on and off. Mine has NEVER blown air at all, yet the blower motor works.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver