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32
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 se-
lected as Continuous, 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 satisfied, the IFC is de-ener-
gized 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; terminal Y1 at 38AUZ unit receives 24-v. 24-v re-
ceived at CADM1 terminal Y. If anti-recycle time delay peri-
od has not expired, CADM1 relay will remain open, de-ener-
gizing Solenoid Valve Relay (SVR) and preventing compres-
sor start. When safety pressure switches are closed and
CADM1 time delay expires, CADM1 relay closes, SVR and
compressor contactor C1 are energized; liquid line solenoid
valve LLSV opens, all outdoor fan motors start and Compres-
sor 1 starts.
As space cooling 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.
38AUZ(D,E)07,08 (Single Circuit/2-Stage)
On a thermostat call for Cooling, IFC will be energized and
indoor (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
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 C1are energized; liquid line so-
lenoid valve LLSV opens, all outdoor fan motors start and
Compressor 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 terminal 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, removing 24-v at
38AUZ(D,E)07,08 terminals Y2 and Y1. Compressor loader
plug is de-energized on Y2 opening. 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 delay.
38AUD (Two Circuit)
On a thermostat call 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 re-
ceived at CADM1 terminal Y. If anti-recycle time delay peri-
od has not expired, CADM1 relay will remain open, de-ener-
gizing Solenoid Valve Relay 1 (SVR1) and preventing com-
pressor 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 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 received at CADM2 terminal Y. If anti-recycle
time delay period has not expired, CADM2 relay will remain
open, de-energizing Solenoid Valve Relay 2 (SVR2) and pre-
venting 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 outdoor fan motors stop and SVR1 re-
lay 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 33 illustrates the factory-installed hot gas bypass
(HGBP) option for 38AUD units. See Fig. 34 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
pressure will decrease which is detected by the HGBP valve
(constant pressure valve). When the suction pressure approach-
es 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 includes a liquid injector (or TXV) which feeds a lit-
tle refrigerant from the liquid line through the TXV to de-su-
perheat the hot gas and maintain an acceptable refrigerant qual-
ity to not damage the compressor. When hot gas bypasses, it re-
duces the mass flow of refrigerant to the evaporator which
reduces its capacity, and attempts to maintain the suction satu-
ration temperature above 32°F (0°C) which minimizes the po-
tential for freeze-up in the evaporator coil.
The HGBP solenoid valve, as indicated in the lower left
of Fig. 33, allows HGBP control during first stage cooling
operation.
Summary of Contents for Gemini 38AU07 Series
Page 5: ...5 Fig 3 38AUD Z 07 14 Base Unit Dimensions ...
Page 19: ...19 Fig 17 Typical Single Circuit Single Stage 38AUZ Wiring Diagrams ...
Page 20: ...20 Fig 18 Typical Single Circuit Two Stage 38AUZ Wiring Diagram ...
Page 21: ...21 Fig 19 Typical Dual Circuit Two Stage 38AUD Wiring Diagram ...
Page 30: ...30 Fig 30 38AUZD E08 Charging Chart RTPF 7 5 Ton Dual Stage Charging Chart R 410A Refrigerant ...
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