First, I still don't have deicers even though the temperature is well below what it should be to trigger the deicers as per the manual.
If you don't see deicers at below 4°C, you either:
1) Don't have the latest version installed. This includes the vehicle updates, which obviously comes with the latest full installer.
OR
2) You are trying to use an unsupported airplane and haven't configured it, indicating the two points over the wings for deicers
OR
3) You are trying to use a supported airplane, but with a wingspan less than 22 meters, which is not supported by the current version of the deicers vehicles.
Second, how do I get an air stairs to show up at an aircraft's service door?
You are not supposed to get any airstairs at the service doors if, with "service doors", you mean the doors on the right side of the fuselage.
Service doors are used only by catering vehicles, and if you airplane is too low to support a catering vehicle with an elevated platform, there will be no stairs, but just a catering minivan.
Airstairs comes only to passenger doors.
