5835254-YIM-A-1119
Johnson Controls Ducted Systems
41
Operation
Cooling sequence of operation
NOTE:
For more in-depth sequence of operation of the Smart
Equipment™ control, refer to the
Smart Equipment™
Controls Sequence of Operation Overview
LIT-
12011950 available from your equipment dealer or
distributor.
For ZZ units, a Y1 call for the first stage of cooling is passed to
the Unit Control Board (UCB) which then determines whether
the requested operation is available and if so, which
components to energize. With a Y1 call for first stage cooling
the UCB determines if a first stage cooling output is valid as
long as all safeties and time-delays allow a C1 output for
cooling. The C1 relay on the UCB closes and sends 24 volts to
the M1 contactor starting the first stage compressor and also
energizing M4 contactor starting the associated condenser
fans. During any call for fan or cooling the FAN output on the
UCB energizes the M3 contactor starting the supply fan.
If a Y2 call is present it is passed to the Unit Control Board
(UCB) which then determines whether the requested operation
is available and if so, which components to energize. With a Y2
call for first stage cooling the UCB determines if a second stage
cooling output is valid as long as all safeties and time-delays
allow a C2 output for cooling. The C2 relay on the UCB closes
and sends 24v to the M2 contactor starting the second stage
compressor also energizing M2 contactor starting the
associated condenser fans. During any call for fan or cooling
the FAN output on the UCB energizes the M3 contactor starting
the supply fan. Lead/lag must be turned off if there are 2 fans
present.
Continuous blower
By setting the room thermostat fan switch to ON, the supply air
blower operates continuously.
Intermittent blower
With the room thermostat fan switch set to AUTO and the
system switch set to either the AUTO or HEAT settings, the
blower is energized whenever a cooling or heating operation is
requested. The blower is energized after any specified delay
associated with the operation.
When energized, the indoor blower has a minimum run time of
30 seconds. Additionally, the indoor blower has a delay of 10
seconds minimum off.
No outdoor air options
When the thermostat calls for the first stage of cooling, the low-
voltage control circuit from R to Y1 and G is completed. The
UCB energizes the economizer (if installed and free cooling is
available) or the first available compressor
*
and the condenser
fans. For first stage cooling, compressor #1 is energized. If
compressor #1 is unavailable, compressor #2 is energized.
After completing the specified fan on delay for cooling, the UCB
energizes the blower motor.
When the thermostat calls for the second stage of cooling, the
low-voltage control circuit from R to Y2 is completed. The
control board energizes the first available compressor. If free
cooling is being used for the first stage of cooling, compressor
#1 is energized. If compressor #1 is active for first stage cooling
or the first compressor is locked-out, compressor #2 is
energized. In free-cooling mode, if the call for the second stage
of cooling continues for 20 minutes, compressor #2 is
energized, provided it has not been locked-out.
If there is an initial call for both stages of cooling, the UCB
delays energizing compressor #2 by 30 seconds in order to
avoid a power rush.
Once the thermostat has been satisfied, it will de-energize Y1
and Y2. If the compressors have satisfied their minimum run
Table 23: Additional static resistance
Size
(tons)
Model
CFM
Cooling only
1
1. Add these values to the available static resistance in the respective blower performance tables.
Economizer
2
,
3
2. Deduct these values from the available external static pressure shown in the respective blower performance tables.
3. The pressure drop through the economizer is greater for 100% outdoor air than for 100% return air. If the resistance of the return air duct is
less than 0.25 IWG, the unit will deliver less CFM during full economizer operation.
4 in. filter
2
Electric heat kW
9
18
24
36
54
15 (15)
ZZ
3700
0.20
0.49
0.27
0.17
0.18
0.21
0.22
0.26
3900
0.23
0.54
0.29
0.19
0.20
0.23
0.24
0.28
4100
0.25
0.58
0.32
0.21
0.22
0.25
0.26
0.31
4300
0.28
0.65
0.35
0.23
0.24
0.28
0.29
0.34
4500
0.30
0.69
0.38
0.25
0.26
0.30
0.31
0.37
4700
0.33
0.74
0.41
0.28
0.29
0.33
0.34
0.40
4900
0.36
0.78
0.44
0.30
0.31
0.35
0.37
0.43
5100
0.39
0.82
0.47
0.33
0.34
0.38
0.40
0.46
5300
0.42
0.86
0.51
0.35
0.37
0.41
0.43
0.49
5500
0.45
0.89
0.55
0.38
0.40
0.44
0.46
0.53
5700
0.48
0.93
0.58
0.41
0.43
0.47
0.49
0.56
5900
0.52
0.96
0.62
0.44
0.46
0.50
0.53
0.59
6100
0.56
0.98
0.67
0.47
0.49
0.53
0.56
0.62
6300
0.60
1.01
0.71
0.50
0.53
0.56
0.59
0.65
