I can finally tell this one!
Back in the 90's the company I worked at upgraded the mainframes from 2 ICL ME29's to a nice shiny ICL Series 39 Lv40 with the corresponding disk cabinet and tape drives for backup. The problem was that the replacement took longer than expected so the air-con in the room was struggling to cope.
Initially this wasn't a problem, the 2 ME29's would run the production work while the S39 was being commissioned, things got a little warm but the S39 was shut down at the end of the day. However once production jobs started running on the new box we couldn't shut it down as easily. As everyone except project managers knows, projects always have snags, in this case it was that some of the batch jobs needed more work before they could be moved over which meant that for a few weeks we would be running both MEs & the S39 from 8am to 11pm.
In the first day it got warm, then hot, then hotter! Then the over-temp alarm in the S39 started going off, a quick check of the manual showed that the alarm would be followed by a shutdown, this would be sub-optimal so a call to the friendly ICL field engineer followed. He told us that there was a reset button located just under the top vents in the box & that pressing it would silence the alarm for 30 mins and cancel the shutdown.
For the next week there was a step-ladder beside the S39, after about midday whoever was on shift would leave the computer room because it was too hot to work in for more than a few mins at a time. When the temperature alarm in the S39 went off, someone would dash in, go up the step-ladder, reach in and hit the alarm reset. This would then repeat every 30 mins throughout the day until all the batch jobs had finished and everything could be shut down. Remote operator consoles were used to monitor things like tape requests etc & these would be done as fast as possible to avoid the heat in the room.
After a week the management had a big chiller unit installed. Of course, after the old Me29s were decommissioned the room was usually too cold to work in because the new chiller was not linked to the air-con and constantly blasted chilled air into the room.