Arrived at customer's house to apply drain solve to 3 units and change a contactor. On arrival turned off unit 1 and changed contactor. Turned unit back on and unit is running fine. Next located air handler units and applied drainsolve to all 3 lines that go down to a 1" common drain And then reduce to a 3/4 outlet. Applied drainsolve and ran hot water behind each drain line. Vacuumed drain line from 3/4 outlet and got a lot of drain debris. Although the Liquid line filter dryer did have Rust on it customer decided to not take preventative action and get filter dryer changed out. All units now running fine. Checked in with customer and customer is happy with work performed. Collected payment and signature and left. Customer happy.