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TH146-P-U 400-280-010-B 5/24/07 3/12
With automatic heating/cooling mode changeover, there’s no need to adjust
the controller at every change of season or weather condition. 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 temperature
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 temperature
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 sched-
ule. 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 main-
tained at the heating setpoint. However, if the temperature rises and
remains above the cooling setpoint for 15 minutes, the controller will
switch to cooling mode.
• When the controller is in cooling mode, the indoor temperature is main-
tained at the cooling setpoint. However, if the temperature drops and
remains below the heating setpoint for 15 minutes, the controller will
switch to heating mode.
Balance Points are used to disable the heat pump or the auxiliary heating
when the outdoor temperature is below or above a set temperature.
• 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.
The auxiliary heat is activated during defrost except under the following con-
ditions:
• 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 sen-
sor 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 controller.
NOTE: The auxiliary heat’s short-cycle protection is disabled during defrost.
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 installa-
tion, the indoor coils are usually installed downstream of the auxiliary
heat source. When the controller is configured for an add-on installa-
tion, the heat pump is disabled during auxiliary heating to prevent over-
pressure.
• 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.
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 cool-
ing stage will be deactivated when the temperature returns to an acceptable
value. The Interstage Delay is fixed at 4 minutes if the controller is config-
ured for an HVAC system and is user-adjustable if it is configured for a heat
pump (see page 8, item 9).
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 activated. If, after a while, the temperature
is still too low, another cooling stage is deactivated and so on. Likewise, dur-
ing heating, if the plenum temperature is higher than HLMT, a heating stage
is deactivated starting with the one that was last activated. If, after a while,
the temperature is still too high, another heating stage is deactivated and so
on. (see page 8, items 10 and 11.)
WARNIN G: 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.
When Smart Fan is enabled (see page 8, item 15), the fan operates as fol-
lows:
• During periods 2 and 4 of automatic mode and during the unoccupied
mode (i.e., when you are away from home or sleeping), the fan oper-
ates 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).
If a humidifier and a dehumidifier are both connected to the controller, the
controller will automatically switch between the two devices to maintain the
desired humidity level. The changeover occurs when the humidity deviates
from the setpoint by more than 3% for 30 minutes.
Dehumidification by droop is a method of dehumidification without using a
dehumidifier. This method is possible only if your system has a cooling
stage. When this feature is enabled (see page 8, item 18), if the humidity
level is too high, the temperature is temporarily lowered below the setpoint
to reduce the indoor humidity level.
NOTE: Dehumidification by droop can cause overcooling.
Dehumidification using an air exchanger will not be efficient if the outdoor
temperature is too high. When an air exchanger is used, the controller will
disable dehumidification if the outdoor temperature is NOT lower than the
indoor temperature by more than 5°C (9°F). When this occurs, the message
HIGH TEMP is displayed.
4. Principles of Operation
4.1
Automatic Heating/Cooling Changeover
4.2
Balance Points (heat pumps only)
4.3
Heating During Defrost (heat pumps only)
4.4
Types of Heat Pump Installations
4.5
Interstage Delay
4.6
Low and High Temperature Limits
4.7
Smart Fan
4.8
Automatic Humidification / Dehumidification Changeover
4.9
Dehumidification by Droop
4.10
Dehumidification by Air Exchanger
400-280-010-B (TH146-P-U) ENG.fm Page 3 Thursday, May 24, 2007 4:28 PM