Evacuation Procedure Electronic Vacuum Gauge

[Refrigerologist]

Hi guys!

I have been using an electronic vacuum gauge for the last 2 years and found something strange happening today!

With 2x 5cfm vac pump running on a remote condensing unit piped to an air handling unit coil, 6okw capacity, the vac gauge stopped at around 1300 -1400 microns. I closed all of the valves in the vaccing lines to prepare to add nitrogen for the final part of the triple vac procedure. When I looked at the vac gauge it had decreased to 350microns. I restarted the vac pumps opened the valves and the vac gauge pressure rose to 800 to 900microns. Closed the lines again and the gauge pressure dropped 350 to 400 microns.

Can anyone explain to me why this would occcur. I should state that the lines were checked for leaks under pressure and the gauge thermistor was cleaned with alcohol as per the manufacturer's instructions.