I understand, and you have picked the problem on these old beasts that takes detective work AND some DIYer skills
Don't fret. See if you got power to the fan using a meter
turn ACC unit on off, hit fan button ect and see if meter reads, if it does then replace blower, if it does not, perhaps pushbutton unit or regualtor or or or...
we can takle that later.
Here is an article by George Murphy, the ACC guru you may find interesting
WHAT GOES WRONG...
Mono-valve: These valves frequently fail to operate because of internal leakage. Generally, the symptoms are no heat on DEF mode or full heat in all modes. Usually the rubber diaphragm inside the valve cracks and leaks. This is easy to repair--you'll need Mercedes-Benz part number 000 835 06 44, Valve Insert
The procedure for repair is as follows
First be sure cooling system pressure is released - allow engine to cool down, then carefully open radiator cap.
Find the mono-valve in the engine compartment on the firewall. Remove the 2- wire electrical connector from the coil, and undo the four assembly screws securing the top of the valve. You may have to loosen the valve mounting bracket to allow room to work on the valve.
Remove the coil (a) and shield (b). Grasp the valve insert (f), and gently pull it (along with washers c, d, and e) straight up and out of the body (g).
Make sure the internal seat inside body (g) is clean; flush with clean water if necessary. Place the new valve insert in the body, making sure the diaphragm seats into the recess in the valve body. Then place washers c, d, and e on the new valve insert in correct order as shown.
Replace shield (b) and coil (a), making sure that the notches between them align so that the coil seats properly. It may protrude slightly due to spring tension of wavy washer (d). Replace the 4 assembly screws and tighten them evenly but not too tight. The body is only plastic, and the threads are easily stripped.
Clean the contact pins and refit the electrical connector. Coil resistance can be checked using an ohmeter - it should read 10-20 ohms; or you can test the assembled valve by connecting 12 volts to the electrical connector pins momentarily. The valve should make a clicking sound.
Refill the cooling system and operate the ACC system through all modes. Check for leaks and proper operation.
Pushbutton Panel
The second most common failure that I have seen is in the pushbutton panel for the climate control.
NOTE: The repair technique outlined below for the printed circuit board has been successful in about two-thirds of the cases that I've encountered, but it is worth a try before replacing this expensive device (about $250 list price).
First, remove the unit from the car as follows: pull the knobs from radio and remove the radio molding. Remove the screws holding the lower edge of the wooden panel, then carefully pry out the lower edge of the panel to uncover the pushbutton unit.
Remove the screws holding the top of the pushbutton panel. You may have to loosen (but do not remove) the bolts in the slots on the housing. Slightly pull out the holder for the pushbutton unit at the top, and lift it out upward.
Pull off the 12-point plugs at the left and right side and the sockets for instrument lights. Remove the holder for pushbutton unit from the unit itself.
Disassembly
Remove the temperature dial by squeezing the plastic spring clips together to allow the clip to release from the pushbutton unit; carefully pry the dial unit away from the main body.
Remove the five pushbuttons from the main unit and the three pushbuttons from the blower switch by pulling them straight outward. If you need to pry with a small screwdriver, insert it under the bottom of the button and apply a counterpressue against the top so the button it is forced outward - it will snap outward off the shaft. Note which button goes where and how it is oriented (make a sketch). Remove the front plastic cover from the unit, held in place by spring clips. Remove the blower switch from the unit in the same manner as the temperature dial. Note how the light diffusers are mounted to the main unit.
Remove the bottom cover from the unit, held in place by plastic spring clips.
Carefully pry the printed circuit boards upward at the rear of the main unit so it will clear the rear of the housing. Slide it upward and out to the rear. The black side panels will probably fall off; note how they are keyed to the grooves in the main housing.
To repair the printed circuit boards, you will need a pencil-type soldering iron of no more than 25 watts, plus a small amount of fine resin core solder wire. These can be obtained at Radio Shack for a few dollars.
Inspect the printed circuit boards for burned-through copper foil. The foil side is a network of thin copper foil conductors soldered at each end to lugs or wire leads of the various parts on the opposite side. The control unit generally fails when one or more soldered connections on the foil side loosen due to vibration or heat. If you are careful, it is possible to resolder the connections and get the unit working again. For this, you'll need a steady hand and the 25-watt soldering iron (and possibly a magnifying glass to inspect your work).
Solidly position the printed circuit board, foil side up, in a well-lighted work area. Starting at one edge of the board, carefully apply heat with the tip of the soldering iron to each solder joint on the board. Caution: apply only enough heat to cause the solder around the connecting wire or lug to momentarily melt, then remove the soldering iron and allow the soldered joint to "freeze". Make sure no solder flows to an adjacent connection, or you'll have a short circuit. If the joint appears to lack enough solder for a good connection, add a small amount. Solid state devices cannot tolerate excessive heat, so use care with the soldering iron.
After you resolder each connection on the board, closely inspect for solder "bridges" between connections, which can cause a short circuit. The connections may appear slightly discolored from your resoldering efforts, but no harm should occur if you were careful with the heat. Be sure to re-solder the fillets between the "side" boards and the "bottom" board - most cracked joints are found here.
Dis-assemble the blower switch and resolder the connections inside. Note how the plastic rocker fits between the two switch halves.
Reassembly
Place the two black side panels on the printed circuit board assembly, and slide it into the main unit at an angle so that the side panels fit into the grooves in the main housing. The assembly will snap into place in the main housing.
Replace the bottom cover. Re-attach the blower switch to the right side of the main housing, then position the light diffusers and attach the front cover to the main housing. Press each pushbutton onto its respective post using the sketch you made during disassembly. Reinstall the unit in the car.
Blower motor: This climate control system operates the blower continuously whenever any button except OFF is pressed. Consequently, after 80-90,000 miles, or 5-6 years, the heater blower motor brushes usually wear down and no longer make good contact with the commutator. This is generally evidenced by a delay of several minutes before the blower starts or it suddenly starts when you hit a bump or hit it with your hand. A new blower can be expensive, so it's worthwhile to remove it and install new brushes. The brushes are fairly soft and can't be purchased from Bosch. (Don't use power tool brushes - they are too hard and will cut a groove in the commutator.)
ACC System Response Sluggish or Operates Too Cold
In M-Bs with automatic climate control, system response can become sluggish as the car (and the system) ages. This can be due to a leaky air tube for the in-car temperature sensor. The sensor is located either adjacent to the right side radio speaker or in the center of the dashboard under a small intake grill. In both cases there is a small (about 1/2" inside diameter) tube connecting the sensor housing to the suction side of the heater blower. The tube allows air to be drawn from the passenger space into the sensor housing to continually expose the sensor to inside air temperature variations.
A portion of the tube consists of foam rubber-like material which, over time, disintegrates. This allows air from under the dash to be drawn directly into the blower, bypassing the air temperature sensor.
You can check air flow around the sensor by pushing the AUTO HI (1977 to 1980) or Blower HIGH button (1981 and up) while the system is running. Place a tissue over the sensor air intake and see if the paper is drawn onto the grill - if no air flow is present, the foam hose is probably disintegrated and needs replacement.
The fix is simple - use 1/2" inside diameter foam insulating tubing for water pipes. It is usually sold in 6 foot lengths and costing about one or two dollars at most hardware stores.
Remove the glove compartment first - it is held in place with 6 or 8 plastic pin assemblies. First remove the inner pin from each assembly, then withdraw the outer pin. Snap the glove compartment light out of its hole, then carefully withdraw the box from the dashboard. Locate the sensor tube and check the foam rubber section for disintegration or blockage. If the foam crumbles easily when handled, it needs to be replaced with a new piece of foam tubing. Use rubber cement will help keep it in place.