When I worked for the US Postal Service my first job was as a BEM or Building Equipment Mechanic. My job was to repair and maintain all of the HVAC equipment in the large buildings. The 1st building I started at was Church Street Station. This building consisted of a 7 story Post Office with a 7 story Office tower on the roof. It is located right next to what used to be the World Trade Center and serves the Wall Street area. All the big brokerage houses used to send their mail here as bulk presort to be put into the system. This building had two 1250-ton Centrifical chillers. The compressors were made by Worthington and driven by steam turbines made by Terry Turbine. These were simple impulse condensing turbines. The input pressure was 160-PSI Steam. A surface condenser with a heat exchanger that was cooled by the roof top cooling tower was located just beyond the turbines exhausts. This rapidly cooled the steam thus in effect creating a vacuum that is sucking the steam through the turbine to cause it to spin. The turbine and compressor rotors were heavy so they ran on hydrostatic babitted bearings. The chiller vessel was of the flooded evaporator type with high and low side floats. I used to maintain the electrical controls on these machines and on the air handlers too. Four of the air handlers for the upper 7 stories in this building were 88,000 CFM capacity each. A few years late I was transferred to work at Morgan Station. This building was 1.2 Million Square feet with 86 air handlers and had four 1500-ton steams drive chillers. I had to work on these too. The Post Office sent me to all the training I needed so I could work on these different pieces of equipment, and I did very well and got promoted to electronic technician within 1 year after starting there.