2004 Caldera Spas Aspire Sensor High Limit Each spa is equipped with a thermistor that is used as temperature sensor. The thermistor is a semiconductor that changes resistance with temperature changes (as the temperature goes up, the resistance goes down). A comparitor circuit then compares the voltage to the set point voltage. If the voltage differs the heating circuit is sent a signal to energize the heater system or teminate the system if voltage is equal to the set point. The set point is the spas default temperature (102°F) unless reset at the control panel's up or down temperature set buttons. NOTE: BYPASSING A THERMISTOR OR SHORTING THE TERMINALS WILL CAUSE THE SPA HEATER TO SHUT DOWN. NEVER ATTEMPT TO BYPASS OR ELIMINATE A THERMISTOR FROM THE CIRCUIT. TO CHECK THE THERMISTOR COMPARE THE RESISTANCE TO THE THERMISTOR CHART. THE WATER TEMPERATURE AND THERMISTOR SHOULD BE THE SAME. Cold Weather Start-ups. In below-freezing climates, technicians and delivery personnel occasionally run into symptoms of electronic high limit tripping when trying to start up a new spa (or a spa that has been stored empty). In the high limit tripped condition, only the circulation pump will operate (the heater, lamp, and jet pump will not operate). The control panel will have four dashes ( ---- ) to indicate the high limit circuit has shut down the spa. High limit tripping at start up is most common in spas that have been stored outside or in unheated areas. This is because thermistors installed in empty spas are sensitive to very cold weather (in filled spas the warm water keeps the thermistor in its normal operating range). If the temperature of the high limit thermistor is near or below 45 degrees F, its resistance increases significantly. The very high resistance of the cold thermistor is outside of the normal operating range, so the high limit circuit shuts down the spa. A second set of thermistors kept in a warm Envioronment Can be switched out prior to powering up the spa. This will keep the system running until the original thermistor warm up. HIGH LIMIT SENSOR Removal: 1. Disconnect power to the spa. 2. Remove the front access panel. 3. Open the control box lid. 4. Unplug the high limit sensor from the control box high limit terminal and remove it from the control box. 5. Trim any zip ties that hold the cords in place. 6. Remove the hi-limit sensor from the clip on the heater. Installation: Reverse the removal procedure to install the control sensor in the equipment compartment taking special care to apply insulation to the backside of the control sensor. Failure to replace the insulation around the high limit and heater will result in the possibilities of the spa shutting down during the winter months. Note: After installation, switch the jet pump to high speed and check spa functions. 2008 Watkins Manufacturing Corporation. CDR is a trademark of Watkins Manufacturing Corporation
