A1 audio = only left ear. A2 audio = only right ear. A3 audio no sound..

I think certain sequence presents (like Broadcast) default to A1 = left, A2 = right, etc.

You can put them back to normal as follows. In the Window menu, go to Audio Track Mixer. In the Audio Track Mixer panel, set the Balance for A1 and A2 to 0. (So the round knob with the line looks vertical.) 

I would not suggest that specific preset, as it is by color space designed for 12 bit RGB media ... Full range ... not the proper limited range for 8/10 bit YUV (Y-CrCb) media that is that vast majority of Rec.709 media.

If you are not sure, you do not have 12 bit RGB designed for full range use.

problem: i've got it, we are selecting the seq. from the broadcast preset and from which we've selected mono discrete, 
Solution: create the seq. from HD 1080p preset and you won't have that problem...
it'll solve that,

I hope it'll help.

also, scree grab of your aidio preferences

Sounds like it's got 'dual mono' ... A1 is left, A2 is right.

If you made a screen grab of your timeline panel showing the control header block to the left, the little icons in the track headers will tell us what you're set to.