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

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 operation is selected as Con-
tinuous, the IFC is energized and the indoor (supply) fan motor
runs continuously. If the thermostat fan operation is selected as
Automatic, the IFC will be energized on a call for Cooling; indoor
(supply) fan motor runs. When thermostat call for Cooling is satis-
fied, the IFC is de-energized and indoor (supply) fan motor stops.
COOLING, UNIT WITHOUT ECONOMIZER
38AUZ(A,B) (Single Circuit)
On a thermostat call for Cooling, IFC will be energized and indoor
(supply) fan motor runs. Thermostat output Y1 is energized; ter-
minal 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 pres-
sure switches are closed and CADM1 time delay expires,
CADM1 relay closes, SVR and compressor contactor C1 are ener-
gized; liquid line solenoid valve LLSV opens, all outdoor fan mo-
tors start and Compressor 1 starts.
As space cooling load is satisfied, thermostat output Y1 is de-ener-
gized, 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.
38AUZ(D,E)07,08 (Single Circuit/2-Stage)
On a thermostat call for Cooling, IFC will be energized and in-
door (supply) fan motor runs. Thermostat output Y1 is ener-
gized; terminal Y1 at either 38AUZ(D,E)07 or 38AUZ(D,E)08
unit receives 24-v. 24-v received at CADM1 terminal Y. If anti-
recycle time delay period has not expired, CADM1 relay will re-
main 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 C1are 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(D,E)07,08 units receive 24-v.
24-v received at CADM1 terminal Y2. CADM1 DC SOL termi-
nal outputs 24-vdc to the compressor loader plug (LDR) and the
compressor operates at full load capacity.
As space cooling load is satisfied, thermostat outputs Y2 and Y1
are sequentially de-energized,
38AUZ(D,E)07,08 terminals Y2 and Y1. Compressor loader plug
is de-energized on Y2 opening. On Y1 opening, Compressor 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 delay.
removing 24-v at
29
38AUD (Two Circuit)
On a thermostat call for Cooling, IFC will be energized and indoor
(supply) fan motor runs. Thermostat output Y1 is energized; ter-
minal 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 en-
ergized; liquid line solenoid valve LLSV1 opens, all outdoor fan
motors start and 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 re-
ceived at CADM2 terminal Y. If anti-recycle time delay period has
not expired, CADM2 relay will remain open, de-energizing Sole-
noid 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 contactor
C2 are energized; liquid line solenoid valve LLSV2 opens and
Circuit 2 compressor starts.
As space cooling load is satisfied, thermostat 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 out-
door 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 delay.
38AUDC12, UNIT WITH HOT GAS BYPASS (HGBP)
Figure 30 illustrates the factory-installed hot gas bypass (HGBP)
option for 38AUD units. See Fig. 31 for the location of the Hot
Gas Bypass. The HGBP is set at about 109 psig (752 kPa) (about
36°F (2°C) saturation temperature), to maintain the evaporator
coil temperatures above 36°F (2°C). The liquid injection valve
(TXV) is set at approximately 17°F (9°C) superheat. The valves
on the HGBP option are preset at the factory, but may be adjusted
in the field.
As the load on the indoor evaporator decreases, the suction pres-
sure will decrease which is detected by the HGBP valve (con-
stant pressure valve). When the suction pressure approaches 109
psig (752 kPa), the HGBP valve begins to open to allow hot gas
from the compressor to bypass to the suction pipe in a controlled
manner to attempt to maintain a constant suction pressure. Since
hot gas is too hot for entering the compressor, the device in-
cludes a liquid injector (or TXV) which feeds a little refrigerant
from the liquid line through the TXV to de-superheat the hot gas
and maintain an acceptable refrigerant quality to not damage the
compressor. When hot gas bypasses, it reduces the mass flow of
refrigerant to the evaporator which reduces its capacity, and at-
tempts to maintain the suction saturation temperature above
32°F (0°C) which minimizes the potential for freeze-up in the
evaporator coil.
The HGBP solenoid valve, as indicated in the lower left of Fig. 30,
allows HGBP control during first stage cooling operation.