Table of Contents
Advertisement
position. Output PL3- - 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, CADM1 relay will remain
open, preventing compressor start. When safety pressure
switches are closed and CADM time delay expires, the
CADM1 relay closes, energizing Solenoid Valve Relay
SVR and compressor contactor C1. SVR contacts close,
energizing the external liquid line solenoid valve.
Solenoid valve LLSV opens. Compressor contactor C1
closes, energizing the compressor motor. Compressor A1
starts and system runs in Stage 1 Cooling mode.
When thermostat calls for Stage 2 Cooling, terminal Y2 is
energized. The 38AUQ's Defrost Board (DFB) receives this
input at P2- - 4. DFB issues 24- - v outputs at OF, P3- - 8
(COMP2). Output PL3- - 8 (COMP2, 24- - v) is received at
CADM2 terminal Y. If anti- - recycle time delay period has
not expired and/or lockout alarms are active, CADM2 relay
will remain open, preventing compressor start. When
CADM2 time delay expires, the CADM2 relay closes,
energizing compressor contactor C2. Compressor contactor
C2 closes, energizing the compressor motor. Compressor A2
starts and system runs in Stage 2 Cooling mode.
As space cooling load is satisfied, thermostat outputs Y2 and
Y1 are sequentially de- - - - energized, removing 24- - v at
terminals Y2 and Y1. Compressor A2 is de- - energized on Y2
opening. On Y1 opening, Compressor A1 stops, all outdoor
fan motors stop and SVR relay is de- - energized. Liquid line
solenoid valve is de- - energized and valve closes. CADM
begins its three- - minute anti- - recycle time delay.
If either the Loss of Charge (LOC) Switch or High
Pressure Switch (HPS) opens while Y1 remains energized,
the compressor contactor C and relay SVR are
de- - energized; 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 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 (RVS) is energized
in Cooling modes. This solenoid will remain energized
until the next Heating mode is initiated.
Fan Cycling
The 38AUQ(D,E)12 is equipped with a temperature
switch that will shut down one outdoor fan 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).
Cooling, Unit With Economizer —
Refer to fan coil unit installation instructions and
economizer
accessory
installation
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); the reversing valve solenoid is de-energized
and the reversing valve moves to Heating position.
DFB issues outputs at OF and P3-10 (COMP1). Outdoor
fan relay OFR is energized; both outdoor fan motors run.
Output PL3-10 (COMP1, 24-v) is received at CADM
terminal Y. If anti-recycle time delay period has not
expired, 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, energizing the
external liquid line solenoid valve. Solenoid valve LLSV
opens. Compressor contactor C closes, energizing the
compressor motor. Compressor starts and system runs in
Heating mode, providing Stage 1 Heat.
When the space heating load is satisfied terminal W1 is
de-energized. Compressor and outdoor fan operations stop.
Liquid line solenoid LLSV is de-energized and valve closes.
CADM begins its three-minute anti-recycle time delay.
If either the Loss of Charge (LOC) Switch or High
Pressure Switch (HPS) opens while, the compressor
contactor C and relay SVR are de-energized; compressor
stops and liquid line solenoid is de-energized (valve
closes). 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 outdoor coil. Defrost sequence will clear the frost and
ice from the coil by briefly reversing the Heating
sequence periodically.
A window to test for a need to run the Defrost cycle opens
at a fixed period after the end of the last Defrost cycle or
the previous test window closed. The window period is
determined by the configuration settings on the DFB's
DIP switches (see unit wiring diagram).
If the outdoor coil's Defrost Thermostat switch (DFT) is
closed (shorting DFB terminals DFT1 and DFT1), the
Defrost cycle will start. Output at OF is removed; outdoor
fans stop during the Defrost cycle. Output P3–7 (RVS1) is
energized; reversing valve solenoid RVS is energized and
instructions
for
reversing valve changes position, placing the circuit in a
Cooling mode flow, directing hot gas into the outdoor coil
where its heat melts the frost and loosens the ice on the
coil face.
29
Advertisement
Table of Contents
