Thermo Scientific ULT-80 Installation & Operation Manual page 48

Loss of Cooling Capacity
Check cooling capacity specifications (see Section II, Specifications).
Check temperature setpoint.
Check to ensure that external heat load has not overcome the cooling
capacity at the desired working temperature.
If the circulator starts and no cooling occurs, listen for a clicking sound from
the inside of the circulator. The clicking is an indication of compressor short-
cycling. Check the following for causes of compressor short-cycling:
If the circulator is shut off for any reason, allow it to remain off for approxi-
mately ten minutes before attempting to restart. The refrigeration compressor
will short-cycle if time is not allotted for the equalization of refrigerant pres-
sures.
Standard circulators are not designed for high temperature applications. If the
cooling coils are subjected to temperatures above the maximum high tempera-
ture for the circulator, compressor short-cycling will occur.
For high-temperature circulators the refrigeration automatically shuts down
above 35°C. The light in the switch will also extinguish.
If the power source is 10% below the circulator's voltage requirements, the
compressor will short-cycle. Check power source for correct voltage output.
When operating below 8°C, a non-freezing solution must be added to the
bath fluid. At low temperature, a higher concentration of the non-freezing
solution is required to prevent ice build up on the circulator's cooling coil. This
ice build up will act as insulation and reduce the cooling capacity. Raise
the temperature of the bath to deice the cooling coil and increase the
concentration of the non-freezing solution. Also, replace the bath fluid periodi-
cally when operating at low temperatures. Moisture concentration in the bath
fluid will increase with time leading to ice buildup.
Circulator Will Not Heat
Check the temperature setpoint to be certain that it is at your desired
temperature (see Section IV, Operator's Loop).
Check the circulator configuration in the controller's Setup Loop.
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