[old man neri]

The way the relay works, to my understanding, is if the rear blower is not working the foot well blowers won't engage.

I had this issue, turned out to be a quick fix. The fuse for the engine blower was corroded.

I would look at the fuse and the relay. Both of these are the left of the engine. The relay is expensive to replace/hard to find so be careful with it.