A stale smell that improves briefly after startup can mean dust on components or a dirty filter

https://winterhavenhvactroubleshooting333.publishlane.com/posts/how-to-spot-an-honest-hvac-company-in-winter-haven-from-the-first-call

A stale smell that improves briefly after startup can mean dust on components or a dirty filter. Replace the filter and have the system cleaned if odors keep returning.