If your HVAC system is broken, weak or insufficient to either pass inspection or meet buyer’s satisfaction, instead of replacing it with a new system, consider replacing it with a good-condition used system.
Many HVAC firms, especially smaller ones, will remove used systems, from other job sites, that are in good working order (because the homeowner wants the latest and greatest system).
Then they will hold onto that used system and sell-install it, for a fee. This often comes with a 3-6 month warranty. And if it will last 3-6 months, it will likely last for several years.
And since they perhaps got the used system for free, they will charge a fraction of the cost of installing a new system. From their perspective, you are basically paying for their time & labor.
As an example, you may be able to expect a 50%-60% discount, over installing a new system.
New HVAC systems are EXPENSIVE. Instead, install a perfectly good working condition used HVAC and pass the savings on to the buyer in the form of your lower pricing of the home.
This makes your home’s pricing all the more attractive on the market and saves you money up front.