Try to keep the distance from the boss throughout the battle. There is no point in fighting at close quarters because the standard attacks cannot damage the robot. Instead, you can be grabbed or hit and lose a lot of health points as a result.
Remember to remain in constant motion. And this is not only to keep the robot at bay, but also to avoid the crates thrown by the boss. In the case of the latter, it is a good idea to make use of avoidance to your aid.
You can win this battle by using the Spammer. In theory, the game itself will suggest using Junk Bolts to immobilize the boss temporarily, but it is best not to waste the Spammer's energy this way. Instead, shoot standard projectiles (the left mouse button/ corresponding game pad button projectiles) at the boss.
During the first phase of the battle with Zorn, focus mainly on attacking one of the robot's upper limbs. After you discernibly weaken this limb, wait for several seconds to replenish the Spammer's energy bar and repeat the shooting. The aim of this action is to weaken the robot's limb during "one take" because, if you deplete the entire energy of the Spammer while shooting, the boss will be able to repair its limb partially.
The first phase finishes when you completely destroy the robot's upper left limb. As soon as phase two of the battle begins, watch out for several new attacks from he boss. This includes a punch to the ground. The best strategy then is to remain outside of the attack's range, combined with avoiding. Start shooting at the upper right limb and, just like earlier, you need to destroy it completely.
As soon as phase three of the battle starts, Zorn will start to implement a new attack, which is releasing the cumulated energy. Act just like previously in the case of the earthquake punch, i.e. stay away from the boss and remember to avoid his attacks.
Notice that Zorn becomes weaker after the discharges of energy (Structural Weakness - the above screenshot). You need to exploit that weakness to your end and take a quick shot at the boss with a Junk Bolt (right mouse button or the corresponding button on your game pad).
If you manage to hit the robot with a Junk Bolt within the specified frame of time, the robot will freeze and you will receive a piece of information about the possibility of termination (the above screenshot). Run up to Zorn and press the interaction key/button.
There is only a QTE event between you and the total victory. The correct combination is kick (right mouse button), punch (left mouse button), kick (right mouse button). For defeating the boss, you will be rewarded with 300 experience points.
[New Journal Entry: Enemy Information- AV-78 Zorn]
Approach the manhole cover once again. This time around, the attempt to leave this location will be a successful one and a new episode will start loading.