How do you know if you have air suspension?

Nope, 4 wheel air suspension was not available on any of the 1992-99 S-class w140 chassis. In 2000 it became standard on the New S-class series in the US. Most S420's were not equipped with the $940 optional Automatic rear-axle level control that consisted of hydropneumatic rear shock absorbers. And never have I seen S420 with the $2700 Active Dampening System shocks (ADS). I am sure there is one out there, but it would have been a special order, most wanting those options opted for the S500 where the level control is standard or the S600 where everything is standard. To know if you have ADS, you will have a selector switch with a picture of a shock absorber on it, just below Climate control, and just above the seat heater switches (if you have the option).

Thanks very much. I didn't think I had the air suspension, but I couldn't figure out how to tell.

Sure, you are welcome.......As a previous w140 (S 500) owner myself, all I can say is, its just one more thing you wont have to worry about having to repair