York Diamond 80 G/UA036SA

Good afternoon. I have a York Diamond 80 G/UA036SA. I am thinking the main drain line is plugged as it is only leaking condensate from the secondary line. I haven't taken the cover off yet, but noticed that there is no trap coming out of the unit, just a straight pvc pipe that ties to another pipe. Can I just cut the pipe and blow into it (perhaps compressed air) to see if the line will become unblocked? I figure I can always add a coupler or add a trap to it to prevent issues in the future.

Does anyone know where I could find the schematic before I climb back into the attic?

Thanks and have a pleasant day.

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