This article describes what to do when there is an HTA alarm followed by an LTA alarm.
HTA is indicated on micro display. After 5 seconds or so, the LTA comes on. I cannot change any set points through programming mode either. Also, I have just replaced both sensors thinking they were the initial trouble.
By the chiller return temperature exceeding the HTA set point. The LTA alarm was probably generated by fluid temp leaving the chiller as it got colder through the chillers refrigeration system. In both cases, the HTA Set point and LTA set point are to close to the chillers programmed set point.
Recommended set point for these alarms:
LTA = SP1 set point -10F
HTA = SP1 set point +15F
It is also important to note that when replacing sensors the location if important. Before doing any reprogramming of micro processor controller, be sure to verify the location of the temperature sensors and make sure they are insulated.
Note: To clear an HTA or LTA alarm momentarily press the chillers power button.