Air Conditioning And Bulding Maintenance For Fun And Profit

Over the past couple of weeks, the building in which I work has been having severe issues with its air conditioning units. The exact cause of the issues had remained largely a mystery, with various and sundry theories being proposed by the building maintenance crew: the newly hot-n’-muggy weather was overloading the system, the coolant systems weren’t functioning correctly, or (my personal favorite) a recent lightning strike burned out the “frequency drive” on one of the condenser units (sounds all science-fiction-y, doesn’t it? “Great Scott! Marty, we can’t go back in time, the frequency drive is on the fritz!”). All of these theories ended up being pure bunk, scientifically speaking, and thus the status quo remained – our AC units adamantly refused to, you know, cool the air like they’re supposed to.
Finally, a breakthrough was made yesterday by our facilities guy.
Clue 1: Another tenant in our building had recently installed a new AC system and had turned it on for the first time about two weeks ago. This timeframe matched up precisely with the first incidence of failure on our system’s part.
Clue 2: Said tenant’s AC system’s control line runs right next to our “malfunctioning” unit’s control line for length of 7-10 feet.
Clue 3: Both control lines are unshielded.
As anyone who has taken elementary electrical engineering classes (or physics classes, for that matter) can tell you, when current is run through a line, it creates a magnetic field around the line which can, in turn, induce current in properly-aligned (read: parallel) adjacent lines.
Ding! A light went on in everyone’s heads. The malfunctioning unit in question was a newer Mitsubishi model with a rather sophisticated microprocessor-driven control system, while the unit installed by the other tenants was an older-style model that apparently relies upon less sophisticated, and thus less sensitive control modules. Every time a control signal was sent up by the other system, it would freak out our system and cause our AC to take itself off-line.
The control lines in question have been re-run and this hopefully marks the end of what has been a bit of a hot and humid two weeks in our office.
Hooray for the Right-hand Rule!