I think the best place to start is to examine the line your rig is on. Are all of the connections - in the service panel, in the receptacle - clean and tight? If it isn’t a dedicated line, have you checked all of the intermediate connections between the service panel and your receptacle? Ideally, you want these connections made with screw terminals - not the "push-through" connectors that many electricians like to use to save time - or with proper wire nut twist-on connectors.
Checking the connections made to your new a/c is also a good idea. Did you get a permit for that work? It would certainly be required where I live, and it never hurts to have an independent inspector examine the work done by a contractor.
You don’t give much information about your Furman unit. Some surge protectors provide only that, and do not "condition" the a/c power. But before trying a Band-Aid approach to your issue, I’d check all of the wiring and connections first. That’s a good thing to do in any event.
Checking the connections made to your new a/c is also a good idea. Did you get a permit for that work? It would certainly be required where I live, and it never hurts to have an independent inspector examine the work done by a contractor.
You don’t give much information about your Furman unit. Some surge protectors provide only that, and do not "condition" the a/c power. But before trying a Band-Aid approach to your issue, I’d check all of the wiring and connections first. That’s a good thing to do in any event.