[TedArnsfret]

Furnace control board went bad so I replaced with an older version. The board part # has been revised 6 times over the years. The bad board was the 5th revision and I've replaced it with the 3rd revision. All works fine, but this got me wondering: What might have changed across the different revisions on these boards? Can I expect any noticeable difference in function or efficiency of the unit?

The only noticeable difference so far is that the relay click is a little louder.

 

[beenthere]

Depends on what the revision reason was. May be that a cheaper relay was used. Or different blower timings were made.

 

[bfletcher7]

If I were you I'd reach out to the manufacturer in hopes that they would answer your concern. Revision level changes could be major or minor. Among some that I've seen in other segments could be migration to RoHS-compliant products, documentation control, design change, etc. Some may or may not up a rev at the top assembly level for a simple Bill of Material change (i.e. a component part number change). And some may or may not up a rev at the top assembly level for a firmware change. In my opinion, any answers provided here would be grasping at straws.