Engineering discipline in real life

I had signed up for frymire services who comes and tune up your AC 2 times a year for some $300 bucks.  This time the technician came and did some work on the AC in attic and then he went outside and did some work on compressor.  Then he left. On that day a cold front came and temp never go above 78 so my AC was not on, for last 2 days temp went above 78 so AC went on but instead of decreasing the temp it was increasing it. Whole night yesterday the temp kept on increasing from 78 to 84 and then decreased from 84 to 80(as the outside temp cooled off). There was a smell of mist in the air also. I was puzzled as to why the heck it was increasing instead of decreasing.  There was some thunderstorm 1 day back and there was an electrical outage also so my first suspicion was that it was because of that I went and tripped the power supply but that had no effect. Now being an enginner I didnt wanted to give up easily, I had no idea what an AC compressor is so googled a bit and thought of tripping it.

I went out side and when I looked at the compressor outlet I was pissed, the stupid technician after cleaning the compressors hadnt put the plug back in so for last 2 days AC was running without compressor( no wonder it wont cool).  I was both thrilled on solving the puzzle but I was also pissed on the technician.  Engineering discipline it seems helps in real life also and it saved me some $150 bucks that frymire would have charged for coming to check on the AC.