4. Principles of Operation
4.1 Automatic Heating/Cooling Changeover
With automatic heating/cooling mode changeover, there’s no need to adjust the controller at every change of season or weather condi- tion. The controller switches automatically between heating mode and cooling mode to maintain the desired temperature.
Manual Mode
When the controller is in manual mode, the heating/cooling mode changeover occurs as follows:
•The controller switches to cooling mode when the indoor tem- perature is higher than the setpoint by more than 1.5°C (2.5°F) for 15 minutes.
•The controller switches the heating mode when the indoor tem- perature is lower than the setpoint by more than 1.5°C (2.5°F) for 15 minutes.
Automatic Mode
When the controller is in automatic mode, it follows the programmed schedule. Two temperature settings (heating setpoint and cooling setpoint) are programmed for each period of the schedule. The heating/cooling mode changeover occurs as follows:
•When the controller is in heating mode, the indoor temperature is maintained at the heating setpoint. However, if the tempera- ture rises and remains above the cooling setpoint for 15 min- utes, the controller will switch to cooling mode.
•When the controller is in cooling mode, the indoor temperature is maintained at the cooling setpoint. However, if the tempera- ture drops and remains below the heating setpoint for 15 min- utes, the controller will switch to heating mode.
4.2 Balance Points (heat pumps only)
Balance Points are used to disable the heat pump or the auxiliary heating when the outdoor temperature is below or above a set tem- perature.
•When the outdoor temperature is below the Balance Point Low (bP L), the heat pump is disabled and only auxiliary heating can be used (see page 8, item 5).
•When the outdoor temperature is above the Balance Point High (bP H), the auxiliary heat is disabled and only the heat pump can be used (see page 8, item 6).
NOTE: Balance Points cannot be used if the AC144-03 outdoor temperature sensor is not connected to the controller.
4.3 Heating During Defrost (heat pumps only)
The auxiliary heat is activated during defrost except under the fol- lowing conditions:
•When the outdoor temperature is above the defrost point (see page 8, item 7). Note: This condition will not apply if the AC144-03 outdoor sensor is not connected to the controller.
•When the plenum temperature is above 40°C (104°F). The auxiliary heat is re-activated when the plenum temperature drops below 32°C (90°F). Note: This condition will not apply if the AC146-410 plenum sensor is not connected to the control- ler.
NOTE: The auxiliary heat’s short-cycle protection is disabled during defrost.
4.4 Types of Heat Pump Installations
The controller can be configured for either of the following types of heat pump installations (see page 8, item 8).
•Add-on Installation: This type of installation is performed when adding a heat pump to an existing furnace. When the heat pump is installed, the furnace becomes the auxiliary heat source. In this type of installation, the indoor coils are usually installed downstream of the auxiliary heat source. When the controller is configured for an add-on installation, the heat pump is disabled during auxiliary heating to prevent overpres- sure.
•New Installation: In this type of installation, as there is not already a furnace, the auxiliary heat source is installed at the same time as the heat pump. In this type of installation, the indoor coils are located upstream of the auxiliary heat. When the controller is configured for a new installation, the heat pump and the auxiliary heat can operate simultaneously.
4.5 Interstage Delay
Interstage Delay is the time allocated for the temperature to return to an acceptable value when it deviates too far from the setpoint. If this time has elapsed, the next heating or cooling stage is activated. The heating or cooling stage will be deactivated when the tempera- ture returns to an acceptable value. The Interstage Delay is fixed at 4 minutes if the controller is configured for an HVAC system and is user-adjustable if it is configured for a heat pump (see page 8, item 9).
4.6 Low and High Temperature Limits
Low Temperature Limit (LLMT) and High Temperature Limit (HLMT) are used to keep the plenum from becoming too cold or too hot. During cooling, if the plenum temperature is lower than LLMT, a cooling stage is deactivated starting with the one that was last acti- vated. If, after a while, the temperature is still too low, another cool- ing stage is deactivated and so on. Likewise, during heating, if the plenum temperature is higher than HLMT, a heating stage is deacti- vated starting with the one that was last activated. If, after a while, the temperature is still too high, another heating stage is deacti- vated and so on. (see page 8, items 10 and 11.)
WARNING: LLMT and HLMT can be used in parallel with an UL353-approved device but they do not replace such device. NOTE: LLMT and HLMT cannot be used if the plenum temperature sensor is not connected to the controller.
4.7 Smart Fan
When Smart Fan is enabled (see page 8, item 15), the fan operates as follows:
•During periods 2 and 4 of automatic mode and during the unoc- cupied mode (i.e., when you are away from home or sleeping), the fan operates only when heating or cooling is activated.
•The fan operates continuously the rest of the time.
NOTE: For Smart Fan to work, set the fan to On (see section 5.3).