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).