Duct Detectors: don’t need em till you need em. While performing startup on multiple pieces of equipment I noticed the OEM duct detectors when tested were failing to shut down the supply fan. Reviewing the manual, setting the dip switches, tracing wiring and correcting the wiring I was able to get every OEM duct detector on every piece of equipment we touched operational and ready for TAB and the fire marshal. DDs can be a huge pain if you don’t understand them. Familiarize yourself with the ope