This one bs. Only spray once maybe, but spray regularly there's really not much need to call for service. The spray will become watery and bring the dirt to the drain pipe, with the condensation over time will help also.

Most important thing is blower, when it is dusty then you feel air weak. Shortcut is spray foam directly on blower but like that very messy. Learn to take apart and wash blower is better, more work but not difficult. Once a year enough, even less if you use air purifier regularly.