Terminal Unit
Control (TUC)
The low temperature detection option protects the unit from freezing conditions by using a capillary line in the coil fins to
detect freezing conditions. The TUC uses the low temperature
sensor with a normally open valve. When the sensor detects
temperatures below 36° F, a binary Figure 31. The low temperature input turns the fan off, closes the sensor is a capillary tube
fresh air damper, disables the inserted into the coil to detect electric heat, and opens the con- freezing conditions.
trol valve. This creates a shutdown
latching diagnostic that requires a reset to resume normal operation. However, normal operation cannot resume until the water temperature rises to 44° F. See Figure 31.Low temperature detection is active even when the unit is off, but the TUC must remain powered for it to be functional.
The factory configures the 24V dry contact input as normally closed to indicate alarm. However, it also can be normally open
if using the correct switch.
Note: While the low temperature detection sensor can help minimize the risk of coil freeze-up, it cannot prevent this from occurring in all circumstances. The user is responsible to adequately protect the unit from freeze conditions.
Note: The capillary line of the low temperature detection sensor is in the section of the hydronic coil above the fan, nearest the control panel box. Locate the outside air wall box or ductwork so fresh air has a direct path into the fan. This allows the sensor to detect an accurate fresh air temperature and proper operation of a dual fan unit. Failure to do this could cause the low temperature detection sensor to incorrectly detect a potential freezing coil.
The condensate overflow detection device protects the unit from condensate water overflow. The switch is a float-type device located in the fan-coil unit’s auxiliary drain pan. See the “Condensate Overflow Switch” section and Figures 12 and 13 on page 26.
When there is a danger of condensate water overflow from the auxil- iary pan, the float rises with the water level in the pan. When the float rises to over 50 percent of its travel, the control valve closes. Also, a binary input causes the fan to turn off, the fresh air damper to close,
97
BIP4: Low
Temperature
Detection Option
BIP3: Condensate
Overflow
Detection Device
