Carrier 38AUQ 16 Series, Installation, Start-Up And Service Instructions Manual

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24
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 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 or Heating; indoor
(supply) fan motor runs. When thermostat is satisfied, the
IFC is de-energized and indoor (supply) fan motor stops.
Cooling, Unit Without Economizer —
When thermostat calls for Cooling, terminal Y1 is
energized. The 38AUQ’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
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 Cooling mode.
When space cooling load is satisfied, terminal Y1 is
de-energized. Compressor and outdoor fan motors stop.
Liquid line solenoid valve 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 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.
Cooling, Unit With Economizer —
Refer to fan coil unit installation instructions and
economizer accessory installation instructions for
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
and/or safety pressure switches are open, outdoor 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
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.
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