I don't really think it's worth messing around with. The system has three modes - fresh air, 80% recirc, and 100% recirc. It automatically runs in 100% recirc mode if the interior of the car is warm enough. I forget the exact value, but in Texas it isn't a problem getting there. Most of the time it operates in 80% recirc mode. Only when the demand for cooling is minimal does it operate in fresh air mode.

The recirc switch forces the system into 100% recirc mode. Rotating the temperature dial to full cold also locks the system in 100% recirc mode.

Based on my (admittedly limited) observations, it's common for the 80% recirc mode to fail (due to a ruptured vacuum diaphram), while the 100% mode still works. This is where my '87 124 is at. In this case manually switching to recirc mode makes a huge difference in how effective the a/c is. I would expect this difference to be amplified in Houston, where humidity removal is a key component of achieving comfort.

You don't want to run in recirc mode all the time - you'll have problems with the windows fogging up in cool weather.

Guess what I'm saying is live with it. If you're really concerned, have an MB-savvy mechanic check the vacuum diaphrams. It's not too difficult, just requires pulling the glove box to access the vacuum tubing/switchover valve and using a small hand vacuum pump (ala Mighty Vac). Replacing the vacuum elements is whole 'nother thing, but testing and diagnosis is quite easy.

- JimY