I have purchased an ACM evaporator with preassembled expansion valve for my 94 E320 (car equipped with factory installed 134A system). I would assume the expansion valve has been pre-torqued by ACM and the o-rings between the expansion valve and the evaporator lines have been moistened with either refrigeration oil or Nylog. But there is no such information provided with the unit. I am wondering if I should go ahead and pull the expansion valve off of the evaporator now and make sure it is correct before I begin the installation. I do not really see why it would ship “preassembled” if it was necessary to do the above, and I hate the idea of breaking the factory seal unless it is necessary. I know the expansion valve can be pulled afterwards if there is a leak at the evaporator lines, but I would obviously like to eliminate that possibility upfront. Can anyone here shed any light on whether this is necessary? There is nothing in the archives on this specific question. Many thanks. John Downey

Is it really possible to install the evap with the expansion valve on it? Or does the expansion valve have to be installed from the engine side after the evap is in?

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2012 E350
2006 Callaway SC560

I put an ACM evap in my 124 wagon late last year.

Don't pull the expansion valve, just leave it in place. It can be easily installed (well, maybe not easily, but it's not any harder...) with the exp. valve already assembled to the evap.

As well, the ACM evap is pressurized, the blocking plate on the other side of the expansion valve has o-rings underneath it. Presumably it is filled with nitrogen, or some other dry, inert gas.

So just leave it alone. When you pull the blocking plate off the exp. valve to install it, you'll have a rush of escaping gas. This will tell you that neither the evap nor the o-rings have a leak.

- JimY

Jim: Thanks for the response. I decided to loosen the backing plate just a bit to see if it was pressurized. I could hear pressure escaping, so the unit clearly is holding whatever pressure was applied at the factory. Therefore, I guess I'm good to go. Thanks again for the info! John

Brewtoo: The Mercedes service CD discusses removing the expansion valve from the old evaporator and transferring it to the new evaporator, prior to installing it as a unit. I'm sure you could do it after the fact as well, but I'm happy it came preassembled. BTW, the new evaporator includes a large 3x5 inch rubber seal mounted on the dashboard side of the expansion valve that apparently seals up a substantial hole in the firewall where the expansion valve protrudes. Hopefully, that means there is room to manuever the unit around a bit.

Yes, the hole through the firewall is pretty big. As well, the ACM has exactly identical dimensions to the original evap. It fits perfect; I didn't have to do any fiddling at all.

One installation hint. When reinstalling the heater box, watch the inlet/outlet pipes for the heater core. They too extend through (smaller) holes in the firewall. It's easy to inadvertently bend one of them. Don't ask how I know... Fortunately repair is equally easy - loosen heater box and work aluminum pipe back into position.

- JimY