Almost every HVAC SEO engagement is sold as one thing and is really five. An agency that is excellent at local work and indifferent about attribution will produce map-pack visibility you cannot prove. One that is strong on content and weak on technical will write pages that never get crawled.
Before you compare suppliers, work out which of the five your problem sits in. The seven pages below each start on a symptom rather than a service, and each one ends by naming a discipline.
Work through it in this order
Can you see yourself in the map results across your whole service area, or only near the office?
If only near the office, that is local.
Owned by Local SEO
Are pages you published months ago still not in Google?
That is technical, and usually crawl or indexation rather than speed.
Owned by Technical SEO
Do you rank for your services but not for the questions people ask before buying?
That is content.
Owned by Content
Are you matched with competitors on everything visible and still below them?
That may be links, and it is worth measuring before assuming.
Owned by Link building
Can you say how many booked jobs came from search last month?
If not, start with attribution, because nothing else can be judged until you can.
Owned by Tracking and attribution
If more than one applies, start with attribution. It is the cheapest to fix and it is the only one that tells you whether the others worked.