Operating Sequence; Base Unit Controls; All Units - Carrier 38AU 16 Series Installation, Start-Up And Service Instructions Manual

OPERATING SEQUENCE

Base Unit Controls

INDOOR (SUPPLY) FAN
If the thermostat fan operation is selected as Continuous the in-
door (supply) fan motor runs continuously. If the thermostat fan
operation is selected as Automatic, the indoor (supply) fan motor
runs when there is a call for cooling, heating, or ventilation. When
thermostat call is satisfied the indoor (supply) fan motor stops. If
there is a fan fault or shutdown condition in the fan coil, the indoor
(supply) fan will not run if there is a call for ventilation, cooling, or
heating, and the 38AU unit will act as if it is not receiving a ther-
mostat demand.
COOLING, UNIT WITHOUT ECONOMIZER
38AUZ (Single Circuit)
On a thermostat call for Cooling the indoor (supply) fan motor
runs (subject to there being no fan fault or shutdown condition, see
above section). 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 pre-
venting compressor start. When safety pressure switches are
closed and CADM1 time delay expires, CADM1 relay closes,
SVR and compressor contactor C1 are energized; liquid line sole-
noid valve LLSV opens, all outdoor fan motors start and Com-
pressor 1 starts.
On a thermostat calling for Stage 2 Cooling, thermostat output Y2
is energized; terminal Y2 at 38AUZ unit receives 24-v. 24-v is re-
ceived at CADM2 terminal Y. If anti-recycle time delay period has
not expired, CADM2 relay will remain open, preventing Com-
pressor 2 start. When safety pressure switches are closed and
CADM2 time delay expires, CADM2 relay closes, compressor
contactor C2 is energized; Compressor 2 starts.
As space cooling load is satisfied, thermostat outputs Y2 and Y1
are sequentially de-energized, removing 24-v at 38AUZ terminals
Y2 and Y1. Compressor 2 stops on Y2 opening. CADM2 begins
its three-minute anti-recycle time delay. On Y1 opening, Com-
pressor 1 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.
38AUD(T,U) (Two Circuits/3-Stage Cooling)
On a thermostat call for Cooling the indoor (supply) fan motor
runs. Thermostat output Y1 is energized; terminal Y1 at 38AUD
unit receives 24-v and the Compressor Lockout Relay (CLR) is
energized (if there is a fan fault or shutdown condition in the fan
coil unit, the CLR will not energize, preventing a Y1, Y2, or Y3
call from turning on the compressors). 24-v is received at CADM1
terminal Y1. 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 en-
ergized; liquid line solenoid valve LLSV1 opens and Circuit 1
compressor starts. On 38AUD*16/25 units, all outdoor fan motors
start, subject to ambient temperature (see Fan Cycling section). On
38AUD*28 units, Outdoor Fans 1 and 2 start, subject to ambient
temperature.
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 pe-
riod has not expired, CADM2 relay will remain open, de-energiz-
ing Solenoid Valve Relay 2 (SVR2) and preventing compressor
start. When safety pressure switches are closed and CADM2 time
delay expires, CADM2 relay closes, SVR2 and compressor con-
tactor C2 are energized; liquid line solenoid valve LLSV2 opens
and Circuit 2 compressor starts. On 38AUD*16/25 units, Outdoor
Fans 3 and 4 start, subject to ambient temperature.
On a thermostat calling for Stage 3 Cooling, thermostat output Y3
is energized; terminal X at 38AUD unit receives 24-v. 24-v is
received at CADM1 terminal Y2. CADM1 DC SOL terminal out-
puts 24-vdc to the compressor loader plug (LDR) and the Com-
pressor 1 operates at full load capacity.
As space cooling load is satisfied, thermostat outputs Y3, Y2 and
Y1 are de-energized, removing 24-v at 38AUD terminals X (Y3),
Y2 and Y1. Compressor 2 loader plug is de-energized on Y3
opening. Circuit 2 compressor stops on Y2 opening; SVR2 is de-
energized and LLSV2 closes. On 38AUD*28 units, Outdoor Fans
3 and 4 stop. 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. On 38AUD*16/25
units, all outdoor fans stop; on 38AUD*28 units, Outdoor Fans 1
and 2 stop. Compressor Lockout Relay is also de-energized.
CADM1 begins its three-minute anti-recycle time delay.
FAN CYCLING
38AUD(T,U)16/25/28 units are equipped with a temperature
switch that will shut down Outdoor Fans 2 and 4 in cooling mode
when the outdoor temperature falls below 55°F (13°C) to ensure
continuous operation in both stages. The outdoor fan will turn
back on when the temperature rises above 60°F (16°C). See
Fig. 30 and 34 for outdoor fan labeling.

All Units

If either the Low Pressure Switch or High Pressure Switch opens
while thermostat output Y1 or Y2 remain energized, the compres-
sor 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 cur-
rent is measured at T1, T2, T3 motor sensors); CADM relay 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 caused by loss of main power,
open compressor internal overload, open low-pressure or high-
pressure switch, or a fault detected by the CADM logic. Compres-
sor operation without cooling may indicate the compressor's
ASTP feature is active; disconnect unit power and allow compres-
sor to cool. See Service section for further details.
COOLING, UNIT WITH ECONOMIZER
Refer to fan coil unit installation instructions and economizer ac-
cessory installation instructions for operating sequences when sys-
tem is equipped with accessory economizer.
HEATING
Refer to fan coil unit installation instructions and accessory heat-
ing device installation instructions for operating sequences in
heating mode.
27