1997 E420 A/C Expansion Valve stuck open?

[Steve M]

1997 E420 with around 125,000. Spring perches sagged around a year and a half ago, resulting in the radiator support scraping and breaking. After a lot of welding, I started to repair A/C problems which I believe were caused by the broken rad support. But after replacing almost everything, I still don't have A/C.

Last May, various diagnoses of leaking condenser, evaporator and compressor shaft seal. System ran well enough to get refrigerant with UV dye into it.

Started last August with a rebuilt compressor I bought on ebay, and had installed, along with a new receiver drier, by a local indy. Even though the original compressor had not failed, he flushed the system anyway. The A/C worked for about a day. The hub on the compressor was spinning, but it wasn't compressing. The indy removed the refrigerant, and said that about 25% of it had leaked.

Ever since then, I don't think the low side has been lower than the high side. In the fall I DIY'd a new condenser, and sent the rebuilt compressor back to the guy who rebuilt it, and he insists it works perfectly (and I don't doubt him). But even though the hub spins, I can add some refrigerant, but it doesn't compress. Without compression, I'm not even creating enough pressure to leak dye.

A few weeks ago I jumped 12 volts directly to the compressor, and kept putting refrigerant in. Both high and low gauges climbed together to about 70 PSI, but no compression, even with the hub spinning. The compressor guy told me it spins a little to circulate oil, but doesn't compress until it sees pressure on the low side (I guess relative to the high side). Suspecting the expansion valve might be stuck open, I also verified old UV dye in the evaporator drain hoses, and decided to bite the bullet.

Bought another drier, evaporator, expansion valve and drier-to-condenser hose (apparently a change MB has made) from Phil. Right now the new parts are in, the dashboard is sitting on the dining room table, but I still don't have A/C.

I harbor suspicions about all of the electrical components, so I am still jumping the compressor to the battery, with the Push Button Unit set to low and the EC light off. I only got a vacuum down to about minus 20 (which holds close to that overnight), so I suspect something may be loose somewhere, but I think I should be able to get enough refrigerant in there to run. But the high pressure reading climbs up right alongside the low, and even though the hub on the compressor spins, there is no compression.

At this point I have replaced all the major components, one of the four hoses and the low side port. I think that covers every single o-ring, unless I'm missing something.

The way I figure it, the high and low sides can only be the same if the expansion valve is stuck open, the compressor is an empty shell, or there is some short circuit or whatever in the manifold gauges. The latter two seem unlikely.

Could a brand new expansion valve be defective? Am I missing something else?

My A/C experience is limited, but I did buy the tools and succcessfully replaced the condenser and drier on the 1996 C280 last fall, so I'm not completely lost