the blower normall has a strip fuse inside a small black plastic elongated "box" about 2 inches long. Mounted on the L fenderwell near the shock towers as I recall. I can take pic if you need one.
There is also a speed regulator ie controller that may have blown. It's a triangular shaped module mounted at the fan housing at the firewall.
I don't know about troubleshooting it, it has a bunch of solid state in it. Most shops use a test module and by substitution find out if its bad. Having a parts car to get test modules from is the cheapest way to go in a situation like this, if you bought a new speed controller and it turned out not the problem you are stuck with it beca seu electrical items are generally not returnable.
Find the fuse first then take it from there. The climate control pushbutton unit iis different in the diesels, I have p/n 1248301885. Don't buy one from a gasser and expect it to work properly, but the fan might run ok if you swapped the gasser module in just the vacuum pods may not be the same, so flaps won't work properly O/W the fan ought to run on and off if you did use a temporary test module in your car from another donor vehicle. YMMV

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!