I am in the midst of replacing the evaporator and 6 vacuum servos on my 1993 400E. The dash and cross brace have been removed. The clips holding the top and bottom halves of the ac/heater box together have been removed. Although the two halves of the ac/heater box have separated on the cabin side of the box, the firewall halves still seem firmly joined. How does the box come apart? Does the heater core need to be removed for the evaporator replacement. Thanks.

Attached Thumbnails

 

The procedure is to remove the entire HVAC box from the car, including both the heater core and the a/c evaporator, then disassemble the box. You will have to drain the engine coolant and remove the heater hoses from the heater core inlet/outlet pipes. Also disconnect the expansion valve.

The box itself is retained by five nuts. Four are on the firewall, one is underneath the box (kinda in front of the radio). Much prying is required to break the sealant used between box and firewall.

Once everything is disconnected and out of the way, the entire box pulls out and is serviced on your workbench. This includes the evaporator, heater core, and all vacuum elements.

- JimY

I was onced faced with replacing the evap on my 320E. Instead I sold it. I had the MB CD ROM shop manuals at one time. These are exremely helpful in cases like this. Try to attact the attention of one of our fellow members who has a manual. You can purchase this software from an MB dealer for around $120.

Thank you, Jcyuhn, your advice got me back on track and the heater box is out! I had removed the sides of the box while it was still in the car, the sides that connect to the ducts going to the outer dash vents. Should the entire box have been removed with the sides still attached?

MB used foam around several of the flaps and around the sides of the heater core. On my car that foam is badly deteriorated. Should I blow away the flaking remnants or do I need to take some other remedial action?

I very much appreciate your taking the time to answer my SOS yesterday.

Frank

Yeah, the box comes out first, then gets disassembled. Suggest you do all the evap/heater core/pods work on the bench. Get a small hand vacuum pump (Mityvac) and bench test the pods.

By removing the sides first, you may have been able to pull the box without removing the ignition cylinder and lock. It blocks the left hand side of the box just enough. I don't have my shop manual handy - ran out of disk space on my office computer - but I think all you do to pull the ignition is insert the key, turn it to position 2, and remove a single allen head bolt. The whole ignition assembly then detaches from the steering column. My memory is a bit fuzzy on it, that's probably close but not exactly right.

Re: the foam, take it all off. I went after it with a shop vacuum. No need to attempt a replacement, the HVAC system works fine without it. You need it to get that perfect, German seal on the doors, but really, you won't miss it. Actually, you're wife or girlfriend (possibly both ) will appreciate not having little black specs of foam deposited on her clothing while riding in your car.

- JimY

Jim, Your memory is just fine; the ignition switch removes pretty much as you described. Even with the sides of the box off, I had to take out the ignition switch to get it to clear. I couldn't find many threads about W124 heater core failures so I am not planning to replace mine. Did you replace yours? What did you do about the disintegrated foam around the heater core? I am wondering if there is a possibility of the core rattling in the box. Thus far, I have spent about 12 hours over 5 days and am going to resume Monday. In the meantime, I occasionally walk out to the garage and gaze at that heater box contraption and pile of interior parts laying on the floor.
Frank

I didn't replace the heater core. Have heard of only one leak - Larry Bible did his within the last year. So I wouldn't worry about it.

I don't remember any foam around the heater core. Guessing that it was completely gone on my car! Sure didn't miss it. Nothing rattled.

Took me about 20 hours total to replace the evap and vacuum elements. Sounds like you are on track for the same.

- JimY