B737 - Audio Control Panel - Degraded mode (ALT-NORM Switch)
 

Hello All

I am learning and training on the 737 NG. Please help me clarify a doubt on ACP degraded mode

FCOM Communication chapter:

DEGRADED AUDIO SYSTEM OPERATION
If the REU or ACP malfunctions, the ACP cannot control the REU. Audio system operation can be switched to a degraded mode by placing the ALT - NORMAL switch to ALT.


There is no QRH NNC for an ACP or REU failure. How will a pilot know if the ACP has failed? Is it by the inability to transmit or receive a call. Can I please have more explanation on this

Thank you in advance
Regards