In the picture, I have a refrigerated HCR Air Door for a open shop in refrigerated cooler box.
The air door drain line connects with the cooler box drain line on the left side of the picture.
After the drain lines connect, they drop down several feet and there is a p-trap going into a floor sink.
BUT my problem is, the Air door drain line is attached to the negative pressure side of the blower compartment. And it has been sucking air through the cooler box drain lines from above, causing any water from the air door coil to be sucked out and whipped up into the blower compartment, causing it to fill with water and leak.
SO I added the P-trap you see in the picture today, figured, if that trap is full of water, the air door won't be sucking through my drain line anymore.
But I'm wondering if I need to install a vent line, before or after the trap?
If so, why?
Is my current p-trap just going to act like a straw without a vent?
I mainly work of refrigerators, and we don't have vents on our drains. But I know most A/C units have vents. Is it because the high negative pressure?