Hart 7080 Error - Refrigeration Turns off

Hello. After the bath has been running for an hour or so, the refrigeration will randomly shut off. When this happens, the display shows PT followed by a bunch of numbers. It doesn't matter whether the bath is in the process of cooling or heating at the time, it still shuts off. I am using gpib to control it, thus the switches on the front has the refrigeration off. After the error, when I send a query, it shows the refrigeration as being set to off. If anyone knows why it is switching off, that would be a big help. Thanks.

OK, you have given us little information on which to provide a sensible answer so let's try again.

The controller is given a response, what controller is it? What is the response? What does the instruction manual say it is?

You are controlling it with a GPIB device, is your software creating the situation ?

What are the operating modes, temperatures and pressures at the time when the refrigeration stops?

Have you checked the 'optional I/O' PCB (connects to main digital control PCB by ribbon cable - worth reseating both ends of said ribbon cable. ) (Hart p/n for this board is 00128430). It is worth reseating all the boards, there are 3 layers of piggybacked boards: the main base PCB with its power supply screws onto the chassis, the digital control PCB plugs into sockets on the main base, and the GPIB interface sits atop the digital control PCB. The 'optional i/o' and display boards as well as the GPIB & RS232 sockets are connected via ribbon cables. The refrigeration compressors are controlled from pin 3 of the J2 socket on the 'optional i/o' board - (brown wire - connects to N/O side of the 'cooling' switch - thus the switch has to be left off to allow the remote I/O to control the compressors). If reseating the boards still results in no joy, check for loose connections and correct mains voltage: this unit can be susceptible to noise. Failing that, it may be necessary to check the GPIB and optional I/O boards by substitution, then try the digital control and base PCB's. If you have another 7080 hot/cold or even a 6020 hot-only bath, you can swap the GPIB controller, digital controller and main base boards out but be aware that the factory calibration values will need to be re-entered if you permanently swap the digital controller.