FORMA 3920 Environmental Chamber

The chamber has been experiencing random temperature control shutdowns with just as random recovery, or with a lab tech power cycling to reset the system.

We had assumed that it was an issue with the control relays again (1 was repalced 2 years ago - arc welded contact - so replaced all three) but they were not the root cause. (the new relays are more robust)

The unit is circa 1995, uses a watlow 985 controller and a Watlow 160[?] Transmitter board for the sensors.

I am thinking it may be either the under or over temp contactors but I dont know refrigeration systems well enough to speculate.

Right click to open diagram in a new window.