Jeff B. phoned me informing me that PT199 had fallen befow 50 psi and wasn't recovering -> Upon arival, I investigated and found that neither the LEAD nor the LAG pressure switches were mechanically closing (my previous "tinkerings" had only been directed at adjustments to the LEAD pressure switch).  Repeated cycles of manually bleeding-off the local receiver tank whilst visually monitoring the mechanical contacts so as to observe if/when they were closing allowed me to adjust the "cut-in" and "span" values of both units. 

I did not find an obvious explaination as what caused the initial problem (only one instance of not working).  My current theory is that there is an imbalance of spring forces occuring on the sheet metal plate which rocks/pivots to open or close the contacts.  There are two springs ("cut-in" spring and range or "span" spring) of differing spring rates which act on this plate.  The mismatched spring forces may be causing the plate to mechanically "bind" too much on its pivot.  As such I altered the spring preload combination a little.  We'll see. 

Anyway, I am leaving the two pressure switches with nearly the same settings in hopes that, at least, one will operated in the desired pressure range.  Though this ought to reduce the compressor run time(s), this is a side effect and isn't part of the motivation for doing this.  

0946 hrs. local -> Leaving site now.