Armstrong World Industries EHU-700 Series User Manual

I/O DIAGNOSTICS
If the display mode selection is left in the diagnostic mode for 10 seconds, the Input/Output 
circuit diagnostic check will begin. The display will show the message C09, the tank will be off, 
and the diagnostics mode light will remain on.

The diagnostics will first check all the output circuits: fill valve, drain valve, 

and tank contactor to make sure they are working. When a light comes on, you will hear the 
corresponding valve or contactor circuit energize for about 2 seconds. Each circuit is checked 
twice before proceeding to the next circuit.

Next the microcontroller checks the status of all input circuits, beginning with 

the control stat. the 3 digit display will show 0% Demand, then the actual stat demand. It will do
this twice. The input diagnostics continues by checking the fan interlock switch, high limit duct 
humidistat, and high water switch. The display will now show C09 followed by any additional 
messages that indicate problems with the input circuits.

When the I/O diagnostic check is finished, the demand mode light will be on, the display will 
show the control stat demand and the unit will return to normal operation. The complete I/O 
diagnostic check lasts less than 2 minutes.

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