Operating Sequence; Base Unit Controls; Indoor (Supply) Fan; Cooling, Unit Without Economizer - Two-Stage Units - Carrier 38AUQ 07-12 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 Cooling or Heating. When thermostat is satisfied, then
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
38AU unit will act as if it is not receiving a cooling or heating
demand.
COOLING, UNIT WITHOUT
TWO-STAGE UNITS
For two stage units, the 38AUQ(D/E)07 uses a two-stage
Copeland ™1 Ultratech Scroll compressor in conjunction with a
two-stage Comfort Alert Module (CADM). The 38AUQ(D/E)12
1. Third-party trademarks and logos are the property of their respective
owners.
Fig. 18 — 38AUQD/E12 Charging Chart
ECONOMIZER —
20
PN: 38AU000486 REV -
uses two compressors in tandem on a single circuit in conjunction
with two single-stage Comfort Alert Modules (CADM).
38AUQ(D/E)07 and 38AUQ(M/N)08
When thermostat calls for Stage 1 Cooling, terminal Y1 is ener-
gized. The 38AUQ unit'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);
both outdoor fan motors start and run. The output RVS1 energizes
the reversing valve solenoid (RVS); Reversing valve switches to
Cooling position. Output PL3-10 (COMP1, 24-v) is received at
CADM terminal Y. If anti-recycle time delay period has not ex-
pired, safety pressure switches are open, and/or lockout alarms are
active, CADM relay will remain open, preventing compressor
start. When safety pressure switches are closed and CADM time
delay expires, the CADM relay closes, energizing Solenoid Valve
Relay SVR and compressor contactor C. SVR contacts close, en-
ergizing the external liquid line solenoid valve. Solenoid valve
LLSV opens. Compressor contactor C closes, energizing the com-
pressor motor. Compressor starts and system runs in Stage 1 Cool-
ing mode.
When thermostat calls for Stage 2 Cooling, terminal Y2 is ener-
gized. The 38AUQ unit's Defrost Board (DFB) receives this input
at P2-4. DFB issues 24-v outputs at OF, P3-8 (COMP2). Output