Is contacting potential customers a good way to raise money (I will not promote)

Me and my business partner are creating software for plumbers, HVAC companies and other trades. The very brief overview is that field technicians of these companies can create proposals, invoices and take pictures of their work on mobile devices while they’re in the field and there is also a web app that does the scheduling for these jobs. The official name of this industry is field service management software and there are many companies that do some variation of it already (but as is the case with all founders I think ours is the best). For the purpose of getting investors I think that a good way would be to pitch to large companies that would potentially use our software. For instance an HVAC company that has more than 100 employees I would think would have some amount of investible money. So essentially we would pitch to companies with the hope that they will “get it” (“get it” meaning they see problems it would solve and the value it would add to their own organization). And we could further develop the software for their needs for some period of time and they would get an ownership percentage in the company. In return we would get an angel investor. I obviously would have to get in touch with companies like this (which I am not sure how to do at the moment) but does this seem like a sensical way to get an investor? I think the traditional angel investor route is out as we do not have any customers at the moment to show how this would scale up from a financial standpoint.