Goofs

After Harry walks into the garbage can, a guy shoots two bullets at them, one hits the corner of the wall the other on the door frame. When they cut back, from MacGyver and Harry, to the guy who shot at them there are two bullet holes on the door frame and no damage to the wall.

The merc "security guard" flips the switch for Elevator#2 to unlock it, then after he dumps the guard in the elevator box, he returns to the guard's desk and flips the switch for Elevator#1 to lock it again, even though that switch had never been moved before.

The female villain shoots the victim with a silenced revolver. Since the cylinder of the revolver is not sealed against the barrel, silencers do not work on revolvers, so the sound would not have been silenced.

An electromagnet powered by DC current would not emit an audible hum the way an AC-powered unit would, so Mac's battery-operated electromagnet would not make any sound.

Faucet-spouts are usually made of brass, not iron, so Mac could not use the spout as the core for his electromagnet.

The episode's title, "Phoenix Under Siege", was misspelled in the opening credits as "Phoenix Under Seige".

Mistake #1 The faucet in the lab was was too easily to take off. It needs to be taken from under sink.

Fact#2 Faucets are usually aluminum, not iron.

The locking-bar is braced against the same windowed door that Mac is peering out of, so the subsequent shot of the door and the lock shows the wrong angle to be a representation of what Mac sees --- Mac's view would be an inverted image of the top end of the locking-bar and its shaft jutting out at a slight angle down to its suction-cup floor-base, not a wide-angle right-side-up "standard" view of the door and lock as seen from across the hallway, as it is shown.

Philips routes hoses under the door of the closet where Mac and his grandfather are and turns on both spigots to full, flooding the closet with hydrogen sulfide gas. The concentration of the gas is likely very high after a few minutes. Mac rubs his clothing to create a spark and even says "that's what we need, just one little spark." He creates a visible spark. Mac would have blown himself and his grandfather up since hydrogen sulfide gas, like methane, is extremely inflammable.

When Mac drives across an intersection on his way to his workplace, the Jeep is travelling on the wrong side of the yellow lines.