The actual intercom function has nothing to do with xmit or receive on the com radio.
You should be able to talk to your self in the head set or to someone wearing the other head set.
The volume knob controls the intercom sound level, the radio volume knob controls the radio receive audio level.
The intercom squelch knob controls what the squelch level of the intercom audio is.
Didn't you get the intercom manual with your avionics kit?
Enter the maintenance mode on the radio by turning it off and pressing the MON button while turning it back on. Adjust the sidetone level using the outer knob to find sidetone level and then the inner knob to select a level. I have mine set to about 15.
Do you have a copy of the maintenance manual for the radio?