Unscheduled Maintenance is a bit of a headscratcher, whilst its effect is potentially useful, it almost feels like the deck needs to support the card, rather than the card supporting the deck.
Because it is a current it lets the runner turn off a corporate current for 1, 1 and 1 card. This effect hardly warrants inclusion in a deck when there are much better currents out there like Hacktivist Meeting or Employee Strike.
The first question is how much impact does this effect have on the corp? That depends on how often the corp will put down more than 1 piece of ice per turn. Lets look at some potential situations:
First turn corp ices R&D and HQ. Problem: Corp gets first turn, so no opportunity for the runner to play Unscheduled Maintanance.
The runner just trashed a lot of Ice on a central server using some combination of Run Amok, Forked, Knifed, Spooned or Parasite etc. This could possibly put the Corp in a position where they would really want to put down a lot of Ice but that also depends on whether they even have more than one Ice in their hand to begin with.
The runner just returned a lot of Ice to the corp's hand using either Leela Patel: Trained Pragmatist's ability or something like a DDoS/Crescentus/False Echo run. Maybe the runner is Leela and wants to just torture the corp using Fisk Investment Seminar to fisk them while they're down.
Maybe the runner just faceplanted into an Architect and the corp wanted to install two pieces of Ice... but will have to 'settle' for just installing one. Solution: Install a sentry breaker before running.
Maybe the runner is running through multiple Cricks without breaking the subroutines. I'm going to assume this is because of hitting a Whirlpool into a Susanoo-No-Mikoto (rather than the runner being insane). Just like the case with the Architect, the corp can just install something else.
The corp is The Foundry: Refining the Process and they have a lot of ice in hand. Solution: Stop triggering the ID ability until the corp either offloads some Ice or gets rid of the current.
The corp mulligans into a terrible iceless hand full of agendas and desperately tries to draw for Ice to protect their centrals and to create a safe remote. Problem: In this situation the runner would much rather have some multiaccess cards to run central servers and score agendas.
The corp has been using Melange Mining Corp. as their only econ card and is now prevented from installing multiple Ice on a non-Melange turn! The same applies if the corp had to spend purging viruses.
Inconvenience Blue Sun: Powering the Future by preventing them from playing the 'Ice Shell Game'.
Out of all these potential cases, the only one that seems even remotely plausible is case 4 and even then most likely Leela will have accessed most of the agendas in that hand already anyway, so the corp won't have to discard too many cards. Also big turns that cause the corp's hand to fill up with Ice tend to use up a lot of s to set up. This means that you would either need to play this card before (spoiling the surprise and risking it being removed) or save another click to play it, in order to get a rather minor effect.
The final analysis is that Unscheduled Maintenance is a dud card because there are very few (if any) situations in the game where the corp needs to install multiple ice in a single turn, these situations are extremely rare and the inconvenience is generally minor. During deckbuilding it is worthwhile asking yourself whether a card either helps you win or prevents your opponent from doing so. This card does neither and is unlikely to provide a return effect that justifies the cost of including and playing it.