York ZV Series Installation Manual Download Page 44

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5370598-BIM-C-0518

Johnson Controls Ducted Systems

Operation

Cooling Operation

• With a demand for first stage cooling either from a

thermostat or space sensor, the low-voltage control circuit
to "C1" and "G" is completed. For first stage cooling, the
compressor is energized and the 1st stage operates (67%
capacity). The UCB will energize the VFD equipped
blower motor at low speed as set in the Smart
Equipment™ control. When the thermostat calls for the
second stage of cooling, the low-voltage control circuit to
"C2" is completed. The control board energizes the 2nd
stage of the compressor (100% capacity). If there is an
initial call for both stages of cooling, the UCB will delay
energizing the 2nd stage of the compressor by 30
seconds in order to avoid a power rush. Once the
thermostat has been satisfied, it will de-energize C1 and
C2. If the compressor has satisfied the minimum run time
(3 min default), the compressors and condenser fans are
de-energized. Otherwise, the unit operates until the
minimum run has been completed. Upon the compressor
de-energizing, the blower is stopped following the elapse
of the fan off delay for cooling.

• To be available, a compressor must not be locked-out due

to a high or low-pressure switch or freezestat trip and the
Anti- Short Cycle Delay (5 min default) must have
elapsed.

Free Cooling Operation with Economizer

• With a demand for first stage cooling either from a

thermostat or space sensor and the outside air is suitable
for free cooling, the dampers will be modulated to
maintain supply air temperature to /- 1 degree of
the Free Cooling SAT Upper Setpoint. If the output to the
economizer actuator is at 10 vdc and the supply air
temperature cannot be controlled to within 5 degrees of
the Free Cooling SAT Upper Setpoint, one compressor
will be energized. The economizer will then be modulated
to maintain supply air temperature to /- 1 degree
of the Free Cooling SAT Upper Setpoint.

• If a demand for second stage cooling occurs and the

economizer is already modulating to maintain the supply
air temperature to the Cooling SAT Upper Setpoint, the
setpoint will be changed to the Free Cooling SAT Lower
Setpoint. Any compressors that are energized will remain
energized and the economizer dampers will be modulated
to maintain supply air temperature to /- 1 degree
of the Cooling SAT Lower Setpoint. If the output to the
economizer actuator is at 10 vdc and the supply air
temperature cannot be controlled to within 5 degrees of
the Cooling SAT Lower Setpoint, compressor stage 2 will
be energized. The economizer will then be modulated to
maintain supply air temperature to /- 1 degree of
the Cooling SAT Lower Setpoint.

• If the output to the economizer actuator is at minimum

position and the supply air temperature drops more than 5

Table 23: Additional Static Resistance

Size

(Tons)

Model

CFM Cooling Only

1. Add these values to the available static resistance in the respective Blower Performance Tables.

Economizer

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” Pleated Filter

Electric Heat kW

-A3 (3)

900

0.05

-0.05

0.01

0.00

0.01

1000

0.05