The high temperature limit sensor is intended for two purposes, either as a slab sensor when the APS C series unit is used for heating side walks, patios or drives or for ambient air temperature when the unit is used for roof and gutter melt systems.
In roof and gutter applications the sensor is run outside the building and placed in a location that is out of direct sunlight and away from other heat sources such as air conditioners or vents.
In slab applications this sensor is usually installed in conduit. If this was not provided for when the slab was poured then the alternative is to either use it as an ambient air sensor or bypass this function all together.
The sensor is not polarized and must be connected to pins 10 and 11. Refer to figure 22 in the manual. If the Class two terminals are black with screw connections problems can occur when the screws are over tightened.
High Limit Thermostat
The calibrated 40°F to 90°F (4°C to 32°C) high limit thermostat prevents excessive temperatures when using constant wattage and MI heaters. It also permits safe testing at outdoor temperatures too high for continuous heater operation. The temperature sensor is included and must be connected to the system for proper operation.
There are two DIP switch configurable operation modes for the high limit thermostat. The factory default operation mode uses the high limit thermostat as a slab temperature regulator, preventing heater operation at temperatures above the set HIGH TEMPERATURE LIMIT. The optional operation mode uses the high limit thermostat as an ambient air sensor, preventing heater operation at temperatures above the set HIGH TEMPERATURE LIMIT until the temperature comes back within limits.
The details of operation in each mode are as follows:
Slab Regulating Thermostat Mode
- High temperature causes unit to turn off heaters, if running, and to ignore any call for heater operation from the panel, RCU or EMC.
- High temperature continues any hold-on cycle that was initiated before the high temperature condition. If the slab temperature drops within limits during the hold-on time the heater will be turned back on.
- In a high temperature condition an APS will still initiate operation of connected SC–40C contactor(s).
- The HEATER CYCLE functions normally.
Ambient Temperature Thermostat Mode
- High temperature causes unit to turn off heaters, if running, and to ignore any call for heater operation from the panel, RCU or EMC.
- High temperature cancels any hold-on cycle that was initiated before the high temperature condition.
- In a high temperature condition an APS will not initiate operation of connected SC–40C contactor(s).
- If the HEATER CYCLE switch is operated in a high temperature condition the heater(s) will be turned on for a maximum of 30 seconds. A new HEATER CYCLE can not be initiated for another two minutes after that.
Bypassing the High Limit Temperature Sensor
If for any reason you need operate the system with out the High Limit Temperature sensor (for trouble shooting or while waiting on a replacement sensor) you can temporarily replace the sensor with a 470K resistor. The resistor will allow the system to run as if the sensed temperature was 40°F (4.4°C).
What size of thermistor should be used in a gutter application?
Hello, Josh.
Unfortunately, we have too little information here to answer this question correctly (6″?) Are you looking for a replacement thermistor on an existing system?
What are you trying to do? Do you mean to use temperature only for your heating system? If so, consider the SST-2, SST-3 or bypass the snow sensor on an APS system and use the high temperature limit to turn off the heat when the temp is above the set point.
While all of these options are viable they are not very efficient because they would leave the heaters on any time the temp was below the set point regardless if water were present.
The more efficient way to ensure the gutters remain clear in the winter would be to use snow sensors that will only turn on the heaters when they are needed during snow or ice events and for a short time afterward to eliminate refreezing of water that has not yet drained away.