Chapter 4 Sequence of operation
52 CNT-SVX05B-EN
Valve operation
This sequence applies to both space temperature control and discharge
air temperature control.
The controller uses analog modulating (0–10 Vdc or 2–10 Vdc) valves for
heating or cooling operation. The controller supports one or two modulat-
ing valves for hydronic heating, steam heat, and hydronic cooling opera-
tion. The Tracer AH540/541 controller supports both one- and two-valve
unit configurations. See Chapter 5, “Configuration”
for more information
about heating and cooling configurations.
Heating only, cooling only, and heating and cooling controller configura-
tions will always use the heating analog output for valve heating and
cooling analog output for valve cooling. For two-pipe changeover configu-
rations with only one hydronic coil installed, use the cooling analog out-
put for heating/cooling valve operation.
Normally, heating and cooling valves remain closed any time the supply
fan is Off. Valves can open when the supply fan is Off during:
• Entering water temperature sampling
• Freeze avoidance
• Certain diagnostic conditions
• Valve override open
The Tracer AH540/541 controller operates with either normally open or
normally closed valves. The normal state of the valve is the position of the
valve when power is not applied. When power is applied, the controller
has full control of the valve. For example, if the fan mode switch on the
zone sensor is in the Off position, the controller closes the valve, regard-
less if it is configured normally open or normally closed.
Freeze-avoidance valve cycling
During low-temperature detect or freeze-avoidance diagnostic conditions
that cause the unit to shutdown, the controller opens all heating and cool-
ing valves 100% to prevent the coil from freezing. When hydronic or
steam heat is present, the controller cycles the heat valve output On, then
Off, over a period of five minutes (configurable) to prevent excessive unit
cabinet temperatures. The heat valve output open position is configurable
from 0 to 100%.
For example, if valve cycling, duty cycle is configured for 25% (default),
the controller opens the valve for 75 seconds (25% of 5 minutes) and
closes it for 225 seconds.
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