York YSCD, Manual, Page: 45 / 108

45
JOHNSON CONTROLS
FORM 145.05-NOM2 (807)
seconds off delay would be turned off. If at any time
the heating demand is lost for two seconds the demand
for second stage operation would be turned off. The
second stage of heating will not start until the fi rst stage
of heating has been turned on.
When the percentage output is equal to or greater than
75% or above, the control will wait 30 seconds and then
initiate a demand for the third stage of operation. If the
percentage output drops to 55% or below, the demand
for third stage operation would continue for 30 seconds.
During this 30 seconds off delay if the percentage
output is equal to or greater than 75% again, the third
stage demand would continue and the 30 seconds off
delay would be turned off. If at any time the heating
demand is lost for one second, the demand for third
stage operation would be turned off. The third stage of
heating will not start until the second stage of heating
has been turned on.
When the percentage output reaches 100%, the control
will wait 30 seconds and then initiate a demand for the
fourth stage of operation. If the percentage output drops
to 80% or below, the demand for fourth stage operation
would continue for 30 seconds. During this 30 second
off delay if the percentage output is equal to 100%
again, the fourth stage demand would continue and
the 30 second off delay would be turned off. If at any
time the heating demand is lost the demand for fourth
stage operation would be turned off. The fourth stage
of heating will not start until the third sate of heating
has been turned on.
Modulating Heat Operation
The Unit Control will send the lower of the supply
air temperature or the return air temperature variable
voltage output to the hydronic heat valve and the valve
will modulate open and close based on the variable
voltage output.
If the freezestat safety switch opens for ten seconds, the
control will send a 50% output to the hydronic valve.
The 50% output signal will continue to be present until
the freezestat circuit closes.
Tristate Modulated Heat
The Tristate Modulated Heat option uses a three position
valve; open, closed and hold. When the variable
percentage output is greater than 50%, the control will
send an open signal to the valve for fi ve seconds. During
this time, the heating capacity will increase. The control
will wait two minutes with the valve in the hold position
(no output). It will then look at the variable percentage
output again. If the output is still greater than 50%, it
will send an open signal to the valve for fi ve seconds.
The control will then wait two minutes with the valve in
the hold position and then look at the variable percentage
output. If the output is still greater than 50%, it will
go through the open sequence again. If the output is
between 10 and 50%, the control will maintain the valve
output in the hold position (no output).
If the output is less than 10%, the control will send a
closed signal to the valve for fi ve seconds. During this
time, the heating capacity will decrease. The control
will wait two minutes with the valve in the hold position
(no output). If the output is still less than 10 %, the
control will initiate a close signal. If the output is
between 10 and 50%, it will remain in the hold mode
(no output). If the output is greater than 50%, the control
will initiate an open signal.
If the freezestat safety switch opens for ten seconds, the
control will ignore the 50% variable percentage output
requirement and will continue to send an open signal
to the valve for fi ve seconds every two minutes as long
as the freezestat switch remains open.
5