An HVAC company sells two things that have almost nothing in common. One is a repair bought in a panic by whoever happens to be home, who calls three numbers off a screen and books the first company that answers. The decision is over before lunch. The other is a system replacement, a purchase big enough that it gets discussed with a spouse, quoted against two or three competitors and closed weeks after the first search.
The season decides which of those is in front of you. The first real heat of the summer and the first hard freeze each produce a week where the phone doesn't stop, and the weeks on either side are quiet enough that owners cut the marketing. Those quiet weeks are exactly when the replacement buyer is doing their reading. Most HVAC advertising runs in the weeks the company is already too busy to answer and goes dark in the weeks the bigger job is being decided.
The third thing worth saying out loud is that the maintenance agreement is the asset, not the paperwork. Whoever holds the agreement is the company that gets called when the system finally dies, which means a repair customer who signs one has been sold a replacement years in advance.