A repair station technician describes finding the “...Kelly Aerospace Combustion Air Pressure Switch (P/N 94E42-3) closed at all times (it has continuity). This is a normally open (N.O.) switch... (which will close) when it senses air pressure at the High Pressure Port. When it is closed at all times, this safety device will tell the heater it has combustion air, whether it's there or not. (This is...) not good if the combustion air blower fails. This 94E42 series switch does not require inspection per AD 2004-21-05 at this time. To prevent reoccurrence, I recommend testing these combustion air pressure switches in conjunction with the Pressure Decay Test mandated by AD 2004-21-05.” (This pressure switch is part of the Kelly Heater Assembly, P/N 37D77-1. The SDRS data base has 12 entries on this switch part number. Aircraft information was not provided. Below are two additional heater defects from the same technician.)

Part Total Time: (unknown).