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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 lo-
cated 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 shutdown con-
dition in the fan coil, then the indoor (supply) fan will not
run if there is a call for ventilation, cooling, or heating and
the CHS 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 ener-
gized. The CHS'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 motors 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 normally open contacts and allowing the Defrost
Board to accept a Y2 thermostat signal. Loader Control
Relay (LCR) is also energized, closing its contacts be-
tween terminals 2 and 4 and allowing the compressor
loader to get energized once the Defrost Board receives
a Y3 thermostat signal.
Output P3-10 (COMP1, 24-v) is received at CADM1 ter-
minal 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, prevent-
ing compressor start. When safety pressure switches are
closed and CADM1 time delay expires, the CADM1 relay
closes, energizing Solenoid Valve Relay SVR1 and com-
pressor contactor C1. SVR1 contacts close, energizing
the external liquid line solenoid valve. Solenoid valve
LLSV1 opens. Compressor contactor C1 closes, energiz-
ing the compressor motor. Compressor 1 starts and sys-
tem runs in Cooling mode.
On a thermostat call for Stage 2 Cooling, terminal Y2 is
energized; 24-v passes through CLR normally open con-
tacts (terminals 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 Cool-
ing 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 clos-
es, energizing the compressor motor on COMP2. Com-
pressor 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 compres-
sor loader plug (LDR) and Compressor 1 operates at full
capacity.
20
As space cooling load is satisfied, thermostat outputs Y3,
Y2, and Y1 are sequentially de-energized, removing 24-v
at CHS terminals X (Y3), Y2, and Y1. Compressor 1
loader plug is de-energized on Y3 opening. Circuit 2
compressor stops on Y2 opening; SVR2 is de-energizied
and LLSV2 closes, and CADM2 begins its three-minute
anti-recycle time delay. On Y1 opening, Circuit 1 com-
pressor stops, all outdoor fan motors stop, and SVR1 re-
lay is de-energized. Liquid line solenoid valve LLSV1 is
de-energized and valve closes. Compressor Lockout Re-
lay 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 Pres-
sure 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 initi-
ates a TRIP event (cooling demand sensed at CADM ter-
minal Y but no current is measured at T1, T2, T3 motor
sensors); CADM relay opens and RED LED is illuminat-
ed. TRIP condition maintains lockout of compressor op-
eration 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 econo-
mizer accessory installation instructions for operating se-
quences when system is equipped with accessory
economizer.
HEATING
When the thermostat calls for first stage heating, terminal
W1 is energized. The CHS's Defrost Board (DFB) re-
ceives this input at P2-7. The DFB removes the output at
P3-7 (RVS1) and P3-6 (RVS2); the reversing valve sole-
noids are de-energized and the reversing valves move to
Heating position.
DFB issues outputs at OF, P3-10 (COMP1), and P3-8
(COMP2). Outdoor fan relay OFR is energized; all out-
door fan motors run.
Outputs P3-10 (COMP1, 24-v) is received at CADM1 ter-
minal Y and P3-8 (COMP2, 24-v) is received at CADM2
terminal Y. If anti-recycle time delay period has not ex-
pired and/or safety pressure switches are open on a par-
ticular 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, energiz-
ing 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). Compressors 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 begins its three-minute anti-recycle time
delay.
Specifications subject to change without notice.
CHS-180-240-01SI Rev. A
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