Here is my step by step version with pics of the evaporator replacement:

1. Notes
___A. I have a 1992 300 TE 4matic. Model 124.290 Engine 103.984.
___B. Sources
______1. Mercedes W 124 Repair Manual
______2. Thread on evaporator My turn for the Evaporator Party
______3. A post on vacuum pods W124 climate control vacuum pod replacement including pictures of pods: http://www.w124performance.com/images/W124___dash/
______4. W123 AC evaporator replacement http://www.peachparts.com/Wikka/W123Evaporator
______5. http://www.peachparts.com/shopforum/showthread.php?p=870494
___C. Steps below in ALL UPPERCASE come from MB Repair Manual on CDROM.
___D. The rest are my addition to the original steps, some of which were derived from other threads on this forum.
___E. All connectors such as screws and nuts were replaced in their original position during disassembly unless a numbered Bag (e.g. Bag3) is noted below. In that case, connector goes in the numbered Ziploc bag and is set aside.
___F. a magnet for retrieving dropped parts is helpful
___G. my system was converted to R134a and I decided to keep it that way for now
2. Parts
___A. R 134a
___B. Nylog blue for R134a system
___C. Vacuum Pump
___D. Initially planned PAG 46 compressor oil / Denso ND8 oil - Q1130001 but since the oil in the current system is unknown, switched to NAPA ester100 oil with dye since it is compatible with PAG and residual mineral oil.
___E. antifreeze
___F. coolant thermostat
___G. Aluminum Mag Wheel Cleaner (acid)
___H. 10” of Tubing ¾” ID 1” OD for AC drainage
___I. Ace Hardware #51278 Open Cell Rubber tape 3/8” x ¾”. Need 5 ft
___J. NAPA #MS 4196 Glass Butyl Tape 3/8” x 15’ for sealing heater core to firewall. Need about 5 ft.
___K. liquid nails
___L. Orings set for heater core A1248350498 (EPCNet 124.290 83 060 26) – ended up not using this as could not get pipes off heater core to replace o rings.
___M. AC
______1. ACM Evaporator A1248300758 (EPCNet 124.290 83 060 104) with attached expansion valve A1408300484 (EPCNet 124.290 83 060 107)
______2. Receiver / Dryer A1248300283 (EPCNet 124.290 83 195 47)
______3. Pressure switch A1248213651 (EPCNet 124.290 83 195 65)
______4. Aux fan Temperature switch A0048206810 (EPCNet 124.290 83 195 56)
______5. AC Oring Kit – only used 4 Orings
___N. lights
______1. Nozzle lights and light for illumination of headlight control N000000001061 x 4 (EPCNet 124.290 54 395 158. Also A0008250094) “air nozzle lighting and rotary switch lighting”
______2. Foglamp indicator bulb: A0025440194 (EPCNet 124.290 54 640 11)
______3. Instrument cluster backlight x 2: N072601012240 (EPCNet 124.290 54 585 53) 3W
______4. Gear shift light N072601012230 (EPCNet 124.290 26 075 116) 1.2W
______5. Climate control unit light x 2. Original is 1.2 W so use gear shift light N072601012230 (EPCNet 124.290 26 075 116) 1.2W
______6. ashtray light N072601012110 (EPCNet 124.290 68 270 53) 2W
___O. Vacuum elements
______1. Right main airflap without dust filter A1248001175 (EPCNet 124.290 83 060 152)
______2. Left main airflap without dust filter A1248000475 (EPCNet 124.290 83 060 143)
______3. Defroster airflap A1248002675 (EPCNet 124.290 83 060 125)
______4. Cold Air airflap A1248000375 (EPCNet 124.290 83 060 140)
______5. Control of shutoff airflaps A1248000275 (EPCNet 124.290 83 060 137)
______6. Legroom airflap A1248000975 (EPCNet 124.290 83 195 152)
3. Job 83-554 (C:\Program Files\MB 300 CDROM\Program\Climate\83-554.pdf )
___A. Have Indy Drain AC (per EPA cannot vent)
___B. Adjust seats all the way back and all the way down
___C. Open sunroof for space and point light from there
___D. Open all windows for ventilation while working
___E. Telescope steering wheel
___F. Disconnect battery and remove
___G. Remove cover on computers to give access to right heater core connections (Pic014). Later hooked up automatic battery charger on 2 amp setting and rolled down windows as had forgotten to do this before – don’t know whether this is ok for electrical system.
___H. Remove grill on air inlet 83-040 (I do not have this PDF)
______1. take off water seal along lower edge of windshield – just pry it off with fingers (Pic001). It is attached by pressure joint (Pic002) in 3 places.
______2. take off seals between engine compartment and hood and between air intake cowling and hood (Pic003)
______3. take off 2 screws from each lateral water drain below windshield, remove white clips by pulling forward (Pic004), and remove water drains. I broke both – part #A1246280228.
______4. unscrew sound proofing between engine compartment and air intake – 4 large plastic nuts/screws (Pic005) and pull soundproofing out then down (Pic006)
______5. remove 2 screws holding sides of air intake assembly (Pic007)
______6. remove 4 tiny screws into molding holding edge of semicircular rubber cover next to base of windshield wiper (Pic008). On assembly be sure to get end of circular molding under adjacent molding (Pic009).
______7. remove critical 2 screws holding air intake assembly down (Pic010). Screws are concealed by engine sound proofing. Also note in picture how lines travel between soundproofing and air intake assembly.
______8. Unclip on both sides (Pic011) and lift out air intake assembly (Pic012).
______9. Need to do all this to get good access to remove power for blower motor, and helps access to evaporator connections and Left heater core connection (Pic013) as well as right heater core connections (Pic014)
___I. DRAIN AC – already done by Indy.
___J. DRAIN COOLANT and replace coolant thermostat. Run at 1500 RPM to refill heat exchanger according to another post.
___K. DISCONNECT HOSES TO HEAT EXCHANGER (2 on right side, 1 on the left. Blow out with compressed air or seal to keep from dripping coolant in car (Pic014) R (Pic015) L. Removed seal from R before pulling BOX. (Pic016).Bag6
___L. DISCONNECT AC LINE CLAMP (Pic017) Bag1
___M. REMOVE MOUNT FOR CHECK VALVE - skipped
___N. PULL PIPES OUT OF EXPANSION VALVE BY LOOSENING NUT. This step delayed until ready to pull BOX (Pic018) Bag7. Had to use 10 mm ignition wrench. Cap the ends with plugs – used those from MityVac. Close R134a filled system fast as compressor oil absorbs moisture However have also read that drawing vacuum pulls moisture back out of oil. During reassembly use new gaskets on AC evaporator fittings and coat with Nylog. My old O rings were black so no O ring swap was done with conversion by dealership. Fill evaporator with 40 ml compressor oil 83-525 (C:\Program Files\MB 300 CDROM\Program\Climate\83-525.pdf ).

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1991 300TE 4matic 205k miles (bought 2000)
1992 300TE 4matic 200k miles (bought 2000)
1992 300TE 4matic 150k miles (bought 2004)