Well both options will have their pros and cons. Additionally, it depends on a lot of factors. However, TYPICALLY (here comes a lot of speculation and generalities) it can be cheaper to take out a HELOC in the long run. They tend to runs around 5-7% which is not much more than your home loan probably is BUT it is a shorter loan. So the loan typically costs less in the long run. However, again, that is dependent on the financing options that you choose for the HELOC. The drawback would be your cash flow. Assuming that you only have about $30 in positive cash flow, your HELOC will probably eat that up plus some.
If you refinanced, yes, it will have an up front cost BUT it can potentially increase your cash flow by lowering your mortgage while accomplishing the goal of replacing the HVAC and maybe even some minor renovations, again depending on how much you can/choose to take out.
I know its a little vague but as with much of real estate, it all comes down to the numbers.Hopefully this at least helps a little and maybe gives you another tool/idea to consider when weighing your options.