835965-UIM-A-0112
Johnson Controls Unitary Products
21
COOLING OPERATION
First-Stage Cooling Operation
During first-stage cooling operation, the control will receive a thermostat
signal at the Y1 terminal. The control will energize the M compressor
output terminal. This signal energizes the coil on the compressor con-
tactor causing the compressor to run.
Second Stage Cooling Operation
During second-stage cooling operation, the control will receive a ther-
mostat signal from Y1 and Y2 inputs. The control will energize both the
M and M2 compressor output terminals. The M signal energizes the
compressor contactor causing the compressor to run. The M2 signal
applies 24VAC to the rectifier plug for the compressor solenoid allowing
the compressor to operate in second stage.
HIGH-PRESSURE SWITCH FAULT
The AC Unit is equipped with a high-pressure switch that is connected
to the control at the HPS terminals. If the high-pressure switch opens
for more than 40 milliseconds, the control will de-energize the compres-
sor and store and display the appropriate fault code. If the pressure
switch closes and a thermostat call for compressor operation is present,
the control will apply the five-minute anti-short cycle delay timer and
start the compressor when the timer expires. If a call for compressor
operation is initiated while the high-pressure switch is open, the control
will use the logic associated with a high-pressure switch opening during
a call for compressor operation.
When the compressor is started following a high-pressure switch fault,
the control will start a six-hour timer based on accumulated compressor
run time. If the control senses another opening of the high-pressure
switch before the timer expires, it will cause a soft lockout condition.
The second opening of the high-pressure switch must be greater than
160 milliseconds for the lockout to occur. If the second opening is
between 40 and 160 milliseconds, the control will de-energize the com-
pressor but not cause a soft lockout condition. If the control does not
sense a second high-pressure switch opening before the six-hour timer
expires, the timer and counter will be reset.
LOW-PRESSURE SWITCH FAULT
The AC unit is equipped with a low-pressure switch which is connected
to the control at the LPS terminals. If the low-pressure switch opens for
more than five seconds, the control will cause a soft lockout condition
and display the appropriate fault codes. If the control experiences multi-
ple soft lockouts the control will enter a hard lockout as described in
another section of this document. However, the control will ignore the
low pressure switch input and not cause a soft lockout condition if it
opens during the following conditions.
•
First two minutes of compressor operation.
•
While TEST input pins are shorted while any thermostat input Y1
or Y2 signal is being received.
OUTDOOR AMBIENT TEMPERATURE SENSOR
Ambient temperature sensor is used in communication applications
only. It is used to display outdoor temperature to the home owner via
the communicating thermostat.
•
Has no effect on operation.
•
Not required for operation, but a fault code will be displayed when
sensor is not connected or if sensor is shorted.
