Operation; Cooling Sequence Of Operation; No Outdoor Air Options - York ZF 180 Series Installation Manual

1061903-XIM-A-0713

Operation

Cooling Sequence Of Operation

For ZF units, the thermostat makes a circuit between "R" and
"Y1" for the first stage of cooling.
The call is passed to the Unit Control Board (UCB), which
then determines whether the requested operation is available
and, if so, which components to energize.
For gas heating, the UCB monitors the "W1" call but does not
handle the operation of the gas furnace. An ignition control
board controls the gas heater operation. For electric heat units,
the UCB passes the call to the electric heater. In both cases,
when the "W1" call is sensed, the indoor air blower is energized
following a specified heating delay.
If at any time a call for both heating and cooling are present, the
heating operation will be performed. If operating, the cooling
system is halted as with a completion of a call for cooling.
Heating always takes priority.
Continuous Blower
By setting the room thermostat fan switch to "ON," the supply
air blower will operate 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 between operations.

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
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 will energize the blower motor.
When the thermostat calls for the second stage of cooling, the
low-voltage control circuit from "R" to "Y2" is completed.
Compressor #2 is energized, provided it has not been locked
out, and condenser fan motor #1, and condenser fan motor #2
remain energized. (If the ambient temperature is above 60ºF.)
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 (ASCD) must have elapsed.
These units utilize a lead-lag feature that results in an equal
amount of run hours on all compressors, thereby extending the
life of the compressors. This feature works as follows: If the
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thermostat requires for more than one stage of cooling, the
currently off compressor with the least number of run hours will
be the next to be energized. When the thermostat requires
fewer stages of cooling, the currently running compressor with
the most run hours will be the first to be de-energized.
Economizer With Single Enthalpy Sensor
When the room thermostat calls for "first-stage" cooling, the low
voltage control circuit from "R" to "G" and "Y1" is completed.
The UCB energizes the blower motor (if the fan switch on the
room thermostat is set in the "AUTO" position) and drives the
economizer dampers from fully closed to their minimum
position. If the enthalpy of the outdoor air is below the set point
of the enthalpy controller (previously determined), "Y1"
energizes the economizer. The dampers will modulate to
maintain a constant supply air temperature as monitored by the
discharge air sensor. If the outdoor air enthalpy is above the set
point, "Y1" energizes compressor #1.
When the thermostat calls for "second-stage" cooling, the low
voltage control circuit from "R" to "Y2" is completed. The UCB
energizes the first available compressor. If the enthalpy of the
outdoor air is below the set point of the enthalpy controller (i.e.
first stage has energized the economizer), "Y2" will energize
compressor #1. If the outdoor air is above the set point, "Y2" will
energize compressor #2. If Y2 brings on compressor #1 and
this condition remains for more than 20 minutes, then
compressor #2 will be energized until the thermostat is
satisfied.
Once the thermostat has been satisfied, it will de-energize "Y1"
and "Y2". If the compressors have satisfied their minimum run
times, the compressors and condenser fans are de-energized.
Otherwise, the unit operates each cooling system until the
minimum run times for the compressors have been completed.
Upon the final compressor de-energizing, the blower is stopped
following the elapse of the fan off delay for cooling, and the
economizer damper goes to the closed position. If the unit is in
continues fan operation, the economizer damper goes to the
minimum position.
Economizer With Dual Enthalpy Sensors
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and the
The operation with the dual enthalpy sensors is identical to the
single sensor except that a second enthalpy sensor is mounted
in the return air. This return air sensor allows the economizer to
choose between outdoor air and return air, whichever has the
lowest enthalpy value, to provide maximum operating
efficiency.
Economizer With Power Exhaust
A unit equipped with an economizer (single or dual enthalpy)
and a power exhaust operates as specified above with one
addition. The power exhaust motor is energized 45 seconds
after the actuator position exceeds the exhaust fan set point on
the economizer control. When the power exhaust is operating,
the second stage of mechanical cooling will not operate. As
always, the "R" to "G" connection provides minimum position
but does not provide power exhaust operation.
Johnson Controls Unitary Products