5 of 12
140
°
F (60
°
C)
Boiler Supply
Supply
Sensor
CAUTION
Improper installation and operation of this control could result in damage to the equipment and possibly even personal injury.
It is your responsibility to ensure that this control is safely installed according to all applicable codes and standards. This
electronic control is not intended for use as a primary limit control. Other controls that are intended and certified as safety limits
must be placed into the control circuit.
STEP ONE
Check the contents of this package. If any of the contents listed are missing or damaged, please contact your sales representative for
assistance.
Type PC705-2 includes:
• PC705-2 Variable Speed Mixing Control • One Outdoor Sensor
• Two Strap on Sensors
• Instruction Sheet
Replacement sensors are available from Taco, Inc. Strap on Sensor – 9300-2044RP Outdoor Sensor – 9300-2052RP
Note:
Carefully read the details of the Sequence of Operation sections in all applicable brochures to ensure that you have chosen the
proper control for your application.
STEP TWO
Installing the Control
• Grasp the front cover by the fingertip grips on the
top and bottom of the enclosure and pull the front
cover off. Remove the wiring cover screw.
• The enclosure is mounted onto a 2” x 4” electrical
box near the Taco Zone Control. Ensure that the
depth of the electrical box is enough to house all
of the wiring that will be in it.
• The mounting holes in the enclosure accept #6
screws.
• Wiring to the control enters the wiring chamber
through the back or bottom of the enclosure.
• To reassemble the enclosure, first replace the
wiring chamber cover and then push the front
cover onto the enclosure until it snaps into place.
The variable speed injection pump and system pump
wiring terminates in the electrical box. All other electri-
cal wiring terminates in the two wiring chambers on the
control. The wiring is roughed-in to the electrical box
prior to installation of the control.
BOILER OPERATION
Boiler Sensor Installed
While the PC705-2 has a mixing demand, the boiler supply water temperature is controlled
by turning the boiler on and off. The PC705-2 calculates the required boiler supply water
temperature based on the load on the mixing system. In order to allow the PC 705-2 to
control the boiler, the Mode switch on the Zone Control must be set to Reset.
The boiler operates around a differential that is automatically controlled by the PC705-2.
The control includes a minimum on and off time for the heat source, in order to minimize
short cycling. The automatic boiler differential increases system efficiency by adjusting to
changing loads.
Boiler Sensor Not Installed
When the PC705-2 has a mixing demand, the boiler turns on and operates off the boiler
operating aquastat. The Mode switch on the Zone Control must be set to Normal in this
application. To improve boiler operation efficiency, the boiler design temperature should
be selected as low as possible, and the injection pump, must then be sized accordingly.
Boiler Protection
When the boiler sensor is installed on the supply side of the boiler the PC705-2 can protect the boiler against flue gas condensation.
When this sensor is installed, the PC705-2 ensures a boiler supply water temperature of at least the Boiler Minimum setting. If the
water temperature is less than the Boiler Minimum setting, the PC705-2 turns on the MIN segment in the LCD and decreases the speed
of the injection pump.
Installation
140
°
F (60
°
C)
Boiler Supply
Supply
Sensor
