PERFECTO2 WITH SENSOR serial no: 191F*******, then: 11FF*******. Over 2 months of desperation. In less than a year, air flow went to a trickle. We paid to send for repair. Returned exactly as sent. Missing filters. We sent it back. Said repaired. They lost in shipping. Deliver a replacement labeled "office. Many phone calls saying low air. Many comments from them that there testing machine said it was in working order. I need oxygen. We finally had to go buy a unit from a reputable company. Told them I give up. My bad. I am out a lot of money. Offered to let them have it back. They told me to trash it. They don't even want them. Needed oxygen. You don't want to gamble your life with their equipment.