I have a 1992 W140 body that is currently in the shop(local MB dealer) for evaporator core ,blower resisitor,and a dash push button unit.I found out that the Evap had been done in '97 by the previous owner. Is this common to be on the 3rd core? I was told by the dealer that all three of these problems are common. Cost to fix all three is 4900.00. THANK GOD FOR AN EXTENDED WARRANTY!!!

Sounds like why extended warrantees cost so much.

I have to be honest here. I have replaced over a hundred evap. cores, but NEVER a pushbutton control unit. The blower regulator is also common.

Good luck

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope :)
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

You are lucky that you are in Columbus and not in Cincinnati. I contacted Ed Potter MB dealership and they said they would do the evaporator on my 92 500 SEL for about $2600. Here in Cincinnati we have only one dealer that wants $4,000 alone just to do the evaporator. I am curious if the evaporator that was replaced in 97 is aluminium? I asked the parts shop and they had a German Aftermarket for $299 compared to the over $600 for the OE. Lee, is the $299 unit made of copper and possibly have a longer life. I would hate to spend $4K here and have to do it again in 3 to 4 years. Also what are the symptoms of a blown regulator resistor because I try to be on the lookout for the common problems of a W-140.

Thanks

The blower regulator is anything but a resister. It is actually more properly described as an end stage amplifier.

It is just a big transister. Basically with the three wires all transistors use: control wire (1-5v from PBC), incoming circuit (from blower), and outgoing circuit (to ground in the 140's case). The 140 also has a term 15 power lead (ignition hot).

As the control signal voltage goes up the connection to ground is made "like" an infinitely variable resistor, but it is done with transistor control.

As to evaporators, I think their problems are much greater in certain areas and certain climates. We don't seem to do as many as shops in large metropolitan areas. I have two theories to this: first is the possibility of air polution/acids facilitating the external corrosion process. Second is the feeling that many large city shops are swayed by the CSI concept I formulated in flourescent dye discussion.

Breifly respoken, many feel that in order to have a good CSI (consumer satisfaction index - no comebacks)it justifies replacing every posible problem. (this is the way I see the first post in this series; was it posssible that you let three major problems accumulate with your A/C ? - it sure is unlikely that they all happened at the same time).

I am seeing a severe decline in many repair skills in my trade due to this concept. How do you all feel about this senario:

Car is brought in with defective A/C manifold assy on a 300e with fuel cooler (a $600 hose). Shop A does the whole job and repairs the hose by cutting the crimped connections and welding new barb fittings and then recrimping modern barrier hose in its place. The job will be the same as Shop B who replaces the hose except the bill will be $500 greater and with a old style rubber hoses. Easy question but now comes the kicker 1 out of 20 welds will have a microscopic leak with a resulting comeback.

To many the possibility of such a comeback is the deciding factor on whether to use such skills and techniques.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician