I'm doing my first pressurization project and I couldn't get the vent to pressurize (1 yellow light). After blocking off a few parts of the room, I figured out the problem was alternating half blocks next to each other. Basically I had a row of lower half blocks next to a large window so that it would seal. After the first row, I used upper half blocks to make the room seem more open.I replaced the second row of half blocks with a full block to transition to the upper half blocks and the room sealed just fine. Just sharing in case anyone else runs into this.