What sort of liability insurance does one need for a sole-proprietor HVAC Repair business?

(CGL) Commercial General Liability

The type of insurance you need is called "Commercial General Liability" also sometimes referred to as "Contractors Liability Insurance"

As an Sole Proprietor providing a repair service you are considered to be engaged in a commercial activity. This type of repair usually comes as a service or repair contract, hence the contractor reference

Good luck

Answer

A local Insurance Broker is the best way to find business insurance. They are not a captive agent like Farmers, State Farm and Allstate. They have the ability to shop the market to get you the best rate.