Alpha Omega: Power and Pack-a-Punch

The power

On Alpha Omega, everything starts in the Power House, the building at the far end of the Cul-de-sac, past Center Street. From the starting area, the way there goes through the Site Entrance and then through either Operations on the right or the APD Interrogation on the left, both of them behind doors.

The Power House

The building that holds the power switch, a large lever. Pulling it lights up the town and opens the way down to the bunker under the houses.

The bunker

The underground half of the map: Lounge, Diner, Beds, Generators, Storage, Solitary and APD Control. It is reached from the backyards of the Green House and the Yellow House.

The gas leak

Once the power is back, the facility computer warns of a Nova 6 gas leak and asks for ventilation. The Pack-a-Punch Machine stays locked until the leak is contained:

Go down to the Generators room and use the terminal by the generators to enable the ventilation systems. The room locks down for about a minute while zombies and Nova 6 Bombers come in. Stock up on ammo before starting it.
When the lockdown ends, the system reports that several ventilation units failed. Back on the surface, four houses leak green Nova 6 gas.
In each of these houses, find the ventilation unit and hold the interact button until the needle of its gauge goes from red to green. Zombies keep coming during the repair, and Jolting Jacks may be waiting on the roofs.
With the fourth unit repaired, the announcement says that the leak is contained, and the Pack-a-Punch Machine opens in the Beds area of the bunker.

Operations

The first building to the right of the starting area: the unit is on a wall of the back-left room.

APD Interrogation

The first building to the left: the unit is outside, on the back wall.

Prisoner Holding

In the room with the cell door, near the back door.

Transfusion Facility

Out of the back door, on the outside wall.

Yellow House

In the garage, past the ground floor.

Green House

Out of the back door, on the wall next to the staircase.

These are the six possible places: only four of them leak in a given game, and the green gas shows which ones.

Green Nova 6 gas leaking inside the Yellow House, Alpha Omega, Call of Duty Black Ops 4 Zombies

A leaking house

The green gas of the Yellow House, one of the six places where a ventilation unit can fail.

The Pack-a-Punch

The machine stands in the Beds, the dormitory of the bunker. Four lights stand next to it, and all four must be green for it to work. Once it is open, Jolting Jacks start to appear among the zombies.

The Pack-a-Punch gives each upgraded weapon an alternate ammo type, and four of them are asked for by the quests of the map: Kill-o-Watt, Cryofreeze, Brain Rot and Fire Bomb, one for each elemental Ray Gun Mark II.

The four elemental Ray Guns

The achievement Nuketown Hustle asks for the Pack-a-Punch Machine to be unlocked by round 5.

In the First Room

Doors closed, none of this can be reached: the Power House is behind the doors of the Site Entrance, so the power stays off, the leak is never contained and the Pack-a-Punch never opens. Jolting Jacks only join the zombies once the machine is open.