Operation; Sequence Of Operations Overview; Cooling Sequence Of Operation; Pressure Drop Across Coil - York ZF036 Installation Manual

Figure 18: Pressure Drop Across Coil

Operation

Sequence Of Operations Overview

For these units, the thermostat makes a circuit between "R" and
"Y1" for the cooling cycle.
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.

Cooling Sequence Of Operation

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.
Johnson Controls Unitary Products
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 cooling, the low-voltage control
circuit from "R" to "Y1" and "G" is completed. The compressor
and condenser fan motor are energized. After completing the
specified fan on delay for cooling, the UCB will energize the
blower motor.
Once the thermostat has been satisfied, it will de-energize Y1. If
the compressor has satisfied its minimum run time, the
compressor and condenser fan de-energize. Otherwise, the
unit operates the cooling system until the minimum run time for
the compressor has been completed. After the compressor de-
energizes, 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 (ASCD) must have elapsed.
Economizer With Single Enthalpy Sensor
When the room thermostat calls for 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 setpoint
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
setpoint, "Y1" energizes the compressor and condenser fan
motor only.
Once the thermostat has been satisfied, it will de-energize "Y1".
If the compressor has satisfied its minimum run time, the
compressor and condenser fan are de-energized. Otherwise,
the unit operates the cooling system until the minimum run
times for the compressor has been completed. After the
compressor de-energizes, 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 min. position.
Economizer With Dual Enthalpy Sensors
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 (Single Or Dual) With Power Exhaust
This system operates as specified above with one addition. The
power exhaust motor is energized 45 seconds after the actuator
position exceeds the exhaust fan setpoint on the economizer
control. When the power exhaust is operating, the second stage
826081-XIM-C-0214
31