Replacing Evaporator on a 420SEL
 

My '87 420SEL A/C (R12 system) stopped working due to a low charge and the trouble was traced to a leaking evaporator. The question I have is: How difficult is it to replace the evaporator and is this a DIY project? Are there any resources with pictures showing how it's done? Thank you. T.C.

very hard, dont bother, either drive it off a cliff or drive w/o A/C

I put some Dura-Cool stop leak in my older 96 S600 and it was still holding fine 2 yrs later.. about 20.00 but well worth it..

oh now you telling us that? i sold mine '94 E420 cause of it, for $3k that was it

wow. are you sure its a leaky evaporator? My mechanic told me it is very rare that
an evaporator leaks on a w126. I seriously thought it was my evaporator leaking inside my car, but it turned out to be my expansion valve.

Great advice :rolleyes:



There's a write up in the Diesel section from R.Leo, he did the one in his old SDL. Not hard, just very time consuming.

Be 100% sure it's the evap core to be bad, as stated it's very rare for the 126s to have this issue. It's more of an early 140/late 124 deal.

Replacing Evaporator on a 420SEL
 

I used an electronic leak detector inside the car. About 5 inches from the front of center vent the indicator would go off consistently. You mentioned that it could be the expansion valve. On other cars I've worked on, the expansion valve is fitted to the evaporator unit. If this is the case, wouldn't it be just as hard to get to the expansion valve as the evaporator or are you saying that the expansion valve in a more accessible area? Also, I've heard that this is one of the weak points in these cars. IIRC, Mercedes changed from a copper evaporator design and went to an all aluminium unit in the mid 80's. Any acid that formed in the system would eat away at the aluminum and cause pinhole leaks in the evaporator.

I had to replace the evap on my 90 560SEL.

Get thee a sniffer and see where the freon is leaking from. For my car, it was alarming whenever I held it in front of the vents.

The expansion valve is under the dash on the left hand side outside of the HVAC plenum, so a leak at the EXP valve will not show up at the vents. You can exchange the exp valve without dissassembly of the HVAC unit.

It's a tedious job, but no harder than the W124 evap I had to exchange on my wife's 95 E320 wagon....

Jim

Exp valve is on driver side, above accelerator pedal. Not hard to swap out, just a PITA

very much so. i had to get line wrench crows feet to do it after trying for three days. I had dye in my system so it was very easy just to look and see it was leaking at the expansion valve. perhaps its possible to sniff the condensation on the ground to see if it comes out positive for refrigerant. it would be worth while to remover the bolster under the steering wheel and check the expansion valve, as it got dye all over the carpet and surrounding area. it seems unlikely that the sniffer would detect refrigerant at the vents if it was only the expansion valve, but stranger things have happened, and as expensive and involved replacing a evaporator is i would check everything before i dove in to that.