66396-YIM-C-1004
Unitary Products Group
27
OPERATION
SEQUENCE OF OPERATIONS OVERVIEW
For these 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 heating, the thermostat makes a circuit between
“R” and “W1” for the first stage of heating. The UCB
energizes all compressors and their condenser fans.
The “W1” call also energizes a separate relay (RW1),
de-energizing the reversing valves allowing the unit to
run in the heating mode. A time / temperature control
operates the defrost cycle.
The thermostat makes a circuit between “R” and “W2”
for the second stage of heating. The UCB passes the
“W2” signal on energizing a relay (RW2), which ener-
gizes the electric heaters if available.
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 oper-
ating, 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 ener-
gized 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. For first stage cooling, compressors #1,
#2, and condenser fan motor #1 are 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 cool-
ing, the low-voltage control circuit from "R" to "Y2" is
completed. Compressors #3, #4, and condenser fan
motor #2, are energized, provided it has not been
locked-out.
If there is an initial call for both stages of cooling, the
UCB will delay energizing compressor #3 and #4, by
30 seconds in order to avoid a power in rush.
Once the thermostat has been satisfied, it will de-ener-
gize 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 fol-
lowing 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 "first-stage" cool-
ing, 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 damp-
ers 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" ener-
gizes the economizer. The dampers will modulate to
maintain a constant supply air temperature as moni-
tored by the discharge air sensor. If the outdoor air
enthalpy is above the setpoint, "Y1" energizes com-
pressors #1, #2 and condenser fan motor #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 setpoint of the enthalpy controller (i.e. first stage
has energized the economizer), "Y2" will energize
compressor circuit #1. If the outdoor air is above the
setpoint, "Y2" will energize compressor circuit #2.
Once the thermostat has been satisfied, it will de-ener-
gize 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
