31
OPERATING SEQUENCE
Base Unit Controls
Indoor (Supply) Fan —
The indoor fan contactor (IFC) is remotely located at the fan
coil or fan section. If the thermostat fan oper ation is selected
as Continuous, the IFC is energized and the indoor (supply)
fan motor runs continuously. If the thermostat fan operation
is selected as Au tomatic, the IF C will be ener gized on a call
for Cooling; indoor (supply) fan motor runs. When
thermostat call for Co olin g is satisf ied, the IF C is
de-ener gized and indoor (supply) fan motor stops.
Cooling, Unit Without Economizer —
38AUZ (Single Circuit)
On a thermostat c all for Cooling, IFC will be energized
and indoor (supply) fan motor runs. Thermostat output Y1
is energized; terminal Y1 at 38AUZ unit receives 24-v.
24-v received at CADM1 terminal Y. If anti-recycle time
delay period has not expired, CADM1 relay will remain
open, de-energizing Solenoid Valve Relay (SVR) and
preventing compressor start. When safety pressure
switches are closed and CADM1 time delay expires,
CADM1 relay closes, SVR and compressor contactor C
are energized; l iquid line solenoid valve LLSV opens, all
outdoor fan motors start a nd Compressor starts.
As space cool ing load is satisfied, thermostat output Y1 is
de--energized, removing 24-v at 38AUZ terminal Y1. On
Y1 opening, Compressor stops, all outdoor fan motors
stop and SVR relay is de-energized. Liquid line solenoid
valve is de-energized and valve closes. CADM1 begins its
three-minute anti-recycle time delay.
38AUD (Two Circuit)
On a thermostat c all for Cooling, IFC will be energized
and indoor (supply) fan motor runs. Thermostat output Y1
is energized; terminal Y1 at 38AUD unit receives 24-v.
24-v received at CADM1 terminal Y. If anti-recycle time
delay period has not expired, CADM1 relay will remain
open, de-energizing Solenoid Valve Relay 1 (SVR1) and
preventing compressor start. When safety pressure
switches are closed and CADM1 time delay expires,
CADM1 relay closes, SVR1 and compressor contactor C1
are energized; liquid line solenoid valve LLSV1 opens, all
outdoor fan motors start a nd Circuit 1 compressor starts.
On a thermostat calling for Stage 2 Cooling, thermostat
output Y2 is energized; terminal Y2 at 38AUD unit
receives 24-v. 24-v received at CADM2 terminal Y. If
anti-recycle time delay period has not expired, CADM2
relay will remain open, de-energizing Solenoid Valve
Rela y 2 (SVR2) and preventing compressor start. When
safety pressure switches are closed and CADM2 time
dela y expires, CADM2 relay closes, SVR2 and
compre ssor contactor C2 are energized; liquid line
solenoid valve LLSV2 opens and Circuit 2 compressor
starts.
As space cooling l oad is satisfied, the rmostat outputs Y2
and Y1 are de--energized, removing 24-v at 38AUD
terminals Y2 and Y1. Circuit 2 compressor stops on Y2
opening; SVR2 is de-energized and LLSV2 closes.
CADM2 begins its three-minute anti-recycle time delay.
On Y1 opening, Circuit 1 compressor stops, all outdoor
fan motors stop and SVR1 relay is de-energized. Liquid
line solenoid valve LLSV1 is de-energized and valve
closes. CADM1 begins its three-minute anti-recycle time
dela y.
All Units
If either the Low Pressure Switch or High Pressure Switch
opens while thermostat output Y1 or Y2 remain energized,
the compressor contactor is de-energized, the compressor
stops and liquid line solenoid is de-energized (valve
closes). CADM initiates a TRIP event (cooling demand
sensed at CADM terminal Y but no current is measured at
T1, T2, T3 motor sensors); CADM re lay opens and RED
LED is illuminated. TRIP condition maintains lockout of
compressor operation until CADM is manually reset.
Reset CADM by cycling unit main power.
Complete system shutdown may be c aused by loss of
main power, open compressor internal overloa d, open
low-pressure or high-pressure switch, or a fault detected
by the CADM logic. Compressor ope ration without
cooling may indicate the compressor’s ASTP feature is
act ive; disconnect unit power a nd allow compressor to
cool. See Service section for further details.
Cooling, Unit With Economizer —
Refer to fan coil unit installation instructions and
economizer accessory installation instructions for
operat ing sequences when system is equipped with
accessory economizer.
Heating —
Refer to fan coil unit ins tallation instructio ns and accessor y
heating device installation instructio ns for op eratin g
sequences in heating mode.
38AU
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