Performed a Mid-Season filter change and operational check. Replaced the air filters on (3)RTU’s and checked the belts. Started and tested the units in heat mode. All systems are operating properly. While performing operational checks, the middle unit, the inducer was running and the system was locked out. The limit switch was open, but the blower was not running to cool off the heat exchanger. Tested the unit, the burner and blower turned on properly but when the heat was satisfied and burner turned off, so did the blower. Normally the blower will run for approximately 1 minute after the burner is off. Found a wire terminal that was loose on a relay for the blower. After crimping the end tighter and reconnecting on the relay, the blower runs after the burner shuts off. The RTU is operating properly. Also the heat exchanger on the back rtu, has a small area on the heat exchanger that is starting to rust and will potentially be a hole in the future. We will monitor the area.