HOW IT OPERATES
The SMC consists of a clock, control circuit, time delays, up to five sensors each located in a Therma-Fuser to sense the air temperature of
that room and a limiting (non-modulating) discharge thermostat. Potentiometers on the control circuit are adjusted using a volt-meter to set the
cooling setpoint for each sensor, a heating offset, a setback setpoint and the discharge air limits.
Lights on the front of the SMC indicate room temperature at the sensors, if the SMC is calling for the cooling or heating mode and the output
signals. A green light for each sensor is on when room temperature is above cooling set point and a red light for each sensor is on when room
temperature is below heating offset. Sensor lights show sensor number when lit. Green and red lights are on for SMC calls for the cooling
mode and heating mode respectively. A yellow light is on when the SMC energizes the fan and either a green or red light is on when either
cooling or heating is energized.
Days and times are set in the clock for the occupied hours and preoccupancy hours of the master zone. The system is in the unoccupied
mode for times other than occupied or preoccupancy.
The SMC will call for continuous fan operation during the occupied and preoccupancy modes and for intermittent fan operation (fan runs only
with a call for heating or cooling) during the unoccupied mode.
During the occupied mode, if room temperature is above the cooling setpoint of any sensor, the SMC will call for the cooling mode. If room
temperature is below the cooling set point of all of the sensors and below the heating offset for at least one sensor, the SMC will call for the
heating mode. Because the SMC will not call for the heating mode unless room temperature at all sensors is below the cooling setpoint, it has
cooling priority. The SMC may be internally switched to heating priority which means it will not call for the cooling mode unless the room
temperature at all sensor is above the heating offset and at least one sensor is above cooling setpoint.
During the unoccupied mode, if room temperature, is below the setback setpoint of any sensor, the SMC will call for heating. Setup instead
of, or in addition to, setback can be internally switched on. With setback, if the room temperature is above the setback setpoint of any sensor
during the unoccupied mode, the SMC will call for cooling.
During the preoccupancy mode, if room temperature is below the heating offset of any sensor, the SMC will call for heating. To provide
cooling pulldown during the summer, the SMC may be internally switched into the occupied mode during preoccupancy times.
When the SMC is calling for cooling or heating, the master zone unit (source of cooling or heating) is controlled by an internal limiting
discharge air thermostat. Cooling output is energized if the SMC is in the cooling mode and the discharge air temperature is above the
cooling discharge air setpoint. Heating output is energized if the SMC is in the heating mode and the discharge air temperature is below the
heating discharge setpoint.
Time delays in the SMC delay changeover between cooling and heating to purge the ducts and allow the system to settle out in ventilation
before changing modes and to improve control stability. Acutherm recommends setting the SMC time delays at 5 minutes for proper
ventilation and purging.
A manual override option can be used to allow occupants to place the system in the occupied mode during unoccupied or pre-occupancy
times. It consists of one or more switches by others located at the occupants convenience. Preferably these switches should be a wind-up
timer to turn off override automatically after a preset time has expired, thus avoiding occupants forgetting to return the system to the
unoccupied mode when finished.
A dirty filter light on the front of the SMC can be used with a differential pressure switch by others to provide an indication of excessive filter
pressure drop.
LOCATION OF SENSOR IN THERMA-FUSER
TF-HC Therma-Fuser With Appearance Panel Removed
