Operating Sequence; Base Unit Controls; Indoor (Supply) Fan; Cooling, Unit Without Economizer - Carrier 38AUQ 25 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, then the
indoor (supply) fan motor, which is remotely located in the fan
coil, runs continuously. If the thermostat fan operation is selected
as Automatic, then the indoor (supply) fan motor runs when there
is a call for Cooing or Heating. When thermostat is satisfied, the
indoor (supply) fan motor stops. If there is a fan fault or a shut-
down condition in the fan coil, then the indoor (supply) fan will
not run if there is a call for ventilation, cooling, or heating and the
38AUQ unit will act as if it is not receiving a cooling or heating
demand.

COOLING, UNIT WITHOUT ECONOMIZER

When thermostat calls for Cooling, terminal Y1 is energized. The
38AUQ's Defrost Board (DFB) receives this input at P2-5. DFB
issues 24-v outputs at OF, P3-7 (RVS1) and P3-10 (COMP1). The
OF output energizes outdoor fan relay (OFR); all outdoor fan mo-
tors start and run, subject to ambient temperature (refer to Fan
Cycling section). The output RVS1 energizes the reversing valve
solenoid 1 (RVS1); Reversing Valve 1 switches to Cooling
position.
Compressor Lockout Relay (CLR) is energized, closing its nor-
mally open contacts and allowing the Defrost Board to accept a
Y2 thermostat signal. Loader Control Relay (LCR) is also ener-
gized, closing its contacts between terminals 2 and 4 and allowing
the compressor loader to get energized once the Defrost Board re-
ceives a Y3 thermostat signal.
Output P3-10 (COMP1, 24-v) is received at CADM1 terminal Y.
If anti-recycle time delay period has not expired, safety pressure
switches are open, and/or lockout alarms are active, then CADM1
relay will remain open, preventing compressor start. When safety
pressure switches are closed and CADM1 time delay expires, the
CADM1 relay closes, energizing Solenoid Valve Relay SVR1 and
compressor contactor C1. SVR1 contacts close, energizing the ex-
ternal liquid line solenoid valve. Solenoid valve LLSV1 opens.
Compressor contactor C1 closes, energizing the compressor mo-
tor. Compressor 1 starts and system runs in Cooling mode.
On a thermostat call for Stage 2 Cooling, terminal Y2 is ener-
gized; 24-v passes through CLR normally open contacts (ter-
minals 2 and 4) and the Defrost Board receives this input at
P2-4. DFB issues 24-v at P3-6 (RVS2) and P3-8 (COMP2).
Output P3-6 energizes Reversing Valve Solenoid 2 (RVS2);
Reversing Valve 2 switches to Cooling position. Output PL3-8
is received at CADM2 terminal Y. If anti-recycle time delay
period has not expired, safety pressure switches on Circuit 2
are open, and/or lockout alarms are active, then CADM2 relay
will remain open, preventing Compressor 2 start. When safety
pressure switches are closed and CADM2 time delay expires,
CADM2 relay closes, energizing Solenoid Valve Relay 2
(SVR2) and compressor contactor C2. SVR2 contacts close,
energizing the external Liquid Line Solenoid Valve 2 (LLSV2).
LLSV2 opens. Compressor contactor C2 closes, energizing the
compressor motor on COMP2. Compressor 2 starts and the
system runs in second-stage cooling mode.
On a thermostat call for Stage 3 Cooling, terminal X (Y3) is
energized. 24-v passes through LCR normally open contacts
(terminals 2 and 4) and enters CADM1-Y2. CADM1 DC SOL
terminal outputs 24-vdc to the compressor loader plug (LDR)
and Compressor 1 operates at full capacity.
As space cooling load is satisfied, thermostat outputs Y3, Y2, and
Y1 are sequentially de-energized, removing 24-v at 38AUQ
terminals X (Y3), Y2, and Y1. Compressor 1 loader plug is de-
energized on Y3 opening. Circuit 2 compressor stops on Y2 open-
ing; SVR2 is de-energized and LLSV2 closes, and 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. Compressor Lockout Relay and
Loader Control Relay are de-energized. CADM1 begins its three-
minute anti-recycle time delay.
If either the Loss of Charge (LOC) Switch or High Pressure
Switch (HPS) on either circuit opens while Y1, Y2, or Y3 remain
energized, then the compressor contactor C and relay SVR on the
corresponding circuit are de-energized; compressor stops and
liquid line solenoid is de-energized (valve closes). Corresponding
CADM initiates a TRIP event (cooling demand sensed at CADM
terminal Y but no current is measured at T1, T2, T3 motor sen-
sors); 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.
Reversing valve solenoid (RVS) is energized in Cooling modes.
This solenoid will remain energized until the next Heating mode is
initiated.

COOLING, UNIT WITH ECONOMIZER

Refer to fan coil unit installation instructions and economizer
accessory installation instructions for operating sequences when
system is equipped with accessory economizer.
HEATING
When the thermostat calls for first stage heating, terminal W1 is
energized. The 38AUQ's Defrost Board (DFB) receives this input
at P2-7. The DFB removes the output at P3-7 (RVS1) and P3-6
(RVS2); the reversing valve solenoids are de-energized and the re-
versing valves move to Heating position.
DFB issues outputs at OF, P3-10 (COMP1), and P3-8 (COMP2).
Outdoor fan relay OFR is energized; all outdoor fan motors run.
Outputs P3-10 (COMP1, 24-v) is received at CADM1 terminal Y
and P3-8 (COMP2, 24-v) is received at CADM2 terminal Y. If
anti-recycle time delay period has not expired and/or safety pres-
sure switches are open on a particular circuit, then outdoor lockout
alarms are active and corresponding CADM relay will remain
open, preventing compressor start. When safety pressure switches
are closed and CADM1 and 2 time delay expires, the CADM 1
and 2 relay closes, energizing Solenoid Valve Relays SVR1 and 2
and compressor contactors C1 and C2. SVR1 and 2 contacts close,
energizing the external liquid line solenoid valves. Solenoid
valves LLSV1 and LLSV2 open. Compressor contactors C1 and
C2 close, energizing the compressor motors. 24-v is also received
at CADM1 terminal Y2 through the Loader Control Relay (LCR)
normally closed terminals 3 and 4. CADM1 DC SOL terminal
outputs 24-vdc to the compressor loader plug (LDR). Compres-
sors start, running at full capacity, and system runs in Heating
mode, providing Stage 1 Heat.
When the space heating load is satisfied terminal W1 is de-
energized. Compressors and outdoor fan operations stop. Liquid
line solenoid LLSV is de-energized and valve closes. CADM be-
gins its three-minute anti-recycle time delay.
If either the Loss of Charge (LOC) Switch or High Pressure
Switch (HPS) on either circuit opens while W1 remains energized,
then the compressor contactor C and relay SVR on the corre-
sponding circuit are de-energized; compressor stops and liquid
line solenoid is de-energized (valve closes). Corresponding
CADM initiates a TRIP event (compressor demand sensed at
CADM terminal Y but no current 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.
Reversing valve solenoid remains de-energized until the next
Cooling cycle is initiated.

DEFROST CYCLE

During the Heating Mode, frost and ice can develop on the out-
door coil. Defrost sequence will clear the frost and ice from the
coil by briefly reversing the Heating sequence periodically.
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