Operating Sequence; Indoor (Supply) Fan; Cooling, Unit Without Economizer; Cooling, Unit With Economizer - Carrier 38AU 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
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-energized and indoor
(supply) fan motor stops.

Cooling, Unit Without Economizer

On a thermostat call for Cooling, IFC will be energized and
indoor (supply) fan motor runs. Thermostat contact TC1
closes; terminal Y1 at 38AU unit receives 24-v. 24-v received
at CADM terminal Y. If anti-recycle time delay period has not
expired, CADM relay will remain open, preventing
compressor start. When safety pressure switches are closed, the
liquid line solenoid valve opens. When CADM time delay
expires, the compressor contactor is energized; both outdoor
fan motors start and compressor starts.
When space cooling load is satisfied, thermostat contacts TC1
open, removing 24-v at 38AU terminal Y. Compressor and
outdoor fan motors stop. Liquid line solenoid valve is
de-energized and valve closes. CADM begins its three-minute
anti-recycle time delay.
If either the Low Pressure Switch or High Pressure Switch
opens while thermostat contact TC1 remains closed, the
compressor contactor is de-energized (both fan motors and
compressor stop) 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.
Complete system shutdown may be caused by loss of main
power, open compressor internal overload, open low-pressure
or high-pressure switch, or a fault detected by the CADM
logic. Compressor operation without cooling may indicate the
compressor's ASTP feature is active (unit sizes 12 and 14
only); disconnect unit power and allow compressor to cool. See
Service section for further details.

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

Refer to fan coil unit installation instructions and accessory
heating device installation instructions for operating sequences
in heating mode.

ROUTINE SYSTEM MAINTENANCE

These items should be part of a routine maintenance program,
to be checked every month or two, until a specific schedule for
each can be identified for this installation:
Quarterly Inspection
(and 30 days after initial start)
Indoor section
• Condenser coil cleanliness checked.
• Return air filter replacement
• Outdoor hood inlet filters cleaned
• Belt tension checked
• Belt condition checked
• Pulley alignment checked
• Fan shaft bearing locking collar tightness checked
• Condensate drain checked

Seasonal Maintenance

These items should be checked at the beginning of each season
(or more often if local conditions and usage patterns dictate):
Air Conditioning
• Condenser fan motor mounting bolts tightness
• Compressor mounting bolts
• Condenser fan blade positioning
• Control box cleanliness and wiring condition
• Wire terminal tightness
• Refrigerant charge level
• Evaporator coil cleaning
• Evaporator blower motor amperage
Heating
• Power wire connections
• Fuses ready
• Manual-reset limit switch is closed
Economizer or Outside Air Damper
• Inlet filters condition
• Check damper travel (economizer)
• Check gear and dampers for debris and dirt
24