So I have tried to use a controller (TYPE 2A), using as monitoring
temperature the cold-side outlet temperature and setting 55 as high
limit cut-out. The upper input temperature is linked to cold-side
outlet temperature too, and the lower input temperature is always 0. In
this way, the controller should always shows a 1 as output control,
except when the temperature to be monitored goes over 55 ºC. However,
this doesn´t run. I find convergence problems (error 203).
Although your problem seems complicated - its actually a very easy fix to
get it to work correctly. Have the high-side inlet temperature to the
controller set to be a constant - in your case the set-point of 55 C is
appropriate. Have the low-side temperature input be connected to the
temperature input that you do not want to exceed. Set the high-limit
cutout to some artificially high value. Set the upper deadband to
something reasonable (2 C for example) and the lower deadband to
0. Connect the output control signal to the input control signal.