- Make two models: one has no options, the other has only Climate Control, schedule both alternately
- Make an assembly line that runs through a single Fit AirCon slot with climate control upgrade purchased
- (Optionally) set Fit AirCon slot to import AirCon module from Local Only, but don't produce any locally --> this will make the bug more obvious
When the upgraded model (with Climate Control) gets there, it fits a single climate control module. When the base model gets there it normally just releases it without doing anything, which is correct. However, the requirement on the base model still shows up as 1 AirCon unit.
This creates two weird scenarios depending on whether or not you told it to use Only Local Aircon modules. If you did, the base model will stop at the slot and refuse to release the car because it can't get any AirCon modules.
The more subtle and expensive behavior, if it can get AirCon modules, is that it will order 4 or 5 and keep them in stock. However, like all slots, since it doesn't consume AirCon modules, after a few cars go through, it'll throw out those AirCon modules, but then order more when the next base model gets there. So you're consuming AirCons even though none are going on cars, and it's wasting time waiting for resources to arrive.
The literal work-around is to use a Smart Junction to send your upgraded models through the Fit AirCon slot, and send your base models around it.