This question is better suited for the heating and airconditioning forum. HVAC is not my trade.
But the condensate line trap is required by code. Among other things, it prevents a backflow of outside air being drawn in through that pipe.
If the discharge end of the line is accessible, a wet-or-dry vacuum applied at the discharge end will clear most blockages almost instantly.

I figured it was a code thing, as there didn't seem to be an actual, rational reason for it. But the use of a wet/dry vac...genius.... I figured it was a hunk of insulation or other detritus right at the threaded discharge connection on the pan. Thanks.

Cheers

If you can;t use a shop vac on the outlet, HVAC guys often carry cans of compressed air (typically used to clean keyboards) to blow it out from the inlet side

I figured it was a code thing, as there didn't seem to be an actual, rational reason for it
It's a code thing AND has an actual, rational reason for it. Bus gave you one of the reasons.
Code things have reasons. They don't just write rules to make headaches for people.