Taco PC705-2 Instruction Sheet

SUPERSEDES: March 1, 2004
Plant ID#: 9300-1057
OUTDR VIEW
°F
Start 10 30 50 70 90 Mixing
% Out Demand
Item
PC705-2
C US
158033
and/or Boiler Pump
(through back of control)
Supply Sensor
Outdoor Sensor
Included
Control Strategy
OUTDOOR RESET
In order to properly control a hot water heating system, the heat supplied to
the building must equal the heat lost by the building.
• The heat supplied to a building is proportional to the temperature of the
water and the surface area of the heating element. A small surface area
such as baseboard radiators requires a higher water temperature than a
larger surface area such as radiant floors.
• The heat lost from a building is dependent on the outdoor temperature. As
the outdoor temperature drops, the building heat loss increases.
Instruction Sheet
PC705-2 Variable Speed Injection Mixing Control
The PC705-2 is a microprocessor-based PID control designed to regulate the supply water tempera-
ture to a heating system by controlling a boiler and the speed of an injection pump. The PC705-2
controls the system supply water temperature based on the outdoor air temperature (outdoor reset). A
boiler sensor can be connected in order to prevent corrosion in the boiler due to flue gas condensa-
tion. If the PC705-2 is controlling the boiler supply water temperature, the control continuously adjusts
the boiler differential in order to optimize the firing cycles of the boiler, prevent large water temperature
swings, and increase the efficiency of the system. A wiring harness is provided to be easily connected
to the Taco Expandable (-EXP) Controls.
The PC705-2 also includes features such as an automatic reset ratio calculation, Warm Weather Shut
Down (WWSD), and a maximum supply water temperature setting.
Control Strategy . . . . . . . . pg. 1
Variable Speed Injection . . pg. 3
Sequence of Operation . . . pg. 4
Installation . . . . . . . . . . . . . pg. 5
Applications . . . . . . . . . . . . .pg. 6
Press & Hold:
Item, to view settings
, to test
Press & Release:
Item + +
Output
System Pump
Do not apply power
1 2 3
Com Sup Out
Input
Included
Input
Power: 24 V ±10% 50/60 Hz 3 VA
Var. Pmp: 120 V (ac) 2.4 A 1/6 hp
Boiler: 24 V (ac) 5 A 1/6 hp pilot 240 VA
Pump: 120 V (ac)
to adjust menu
OUTDR VIEW
°F
Start 10 30 50 70 90 Mixing
Demand
% Out
Item
PC705-2
C US
158033
Signal wiring
4
must be rated
Boil
Made in Canada
at least 300V
Input
Boiler Sensor
Included
Outdoor
Temperature
Drop
1 of 12
102-098
EFFECTIVE: March 2, 2016
Control Adjustments . . . . . . . . pg. 9
Display Operation . . . . . . . . . . pg. 10
Troubleshooting . . . . . . . . . . . pg. 11
Error Messages . . . . . . . . . . . . pg. 12
Settings . . . . . . . . . . . . . . . . .
Output
Variable Speed
Injection Pump
(through back of control)
To Taco
Zone
Control
Constant
Room Temperature
pg. 9
Heat
Loss
Increases