Carrier 38AQ Specifications download pdf (Page 21)

Never charge liquid into the low-pressure side of system.

Do not ovemharge. During charging or removed of refriger-

ant, be sum indoor-fan system is operating.

Chmge unit on cooling cycle only. If unit is charged on

heating cycle, overch;uging may occm:

Checking Heating Cycle Operation -- Place ther-

mostat selector switch at HEAT and reset the space set

point above mnbient temperature so that a call for heating is

ensured. Compressor will start within 5 minutes. Observe

system operation.

Check Compressor Oil Level (38AQS) --After ad-

justing the refngerant charge, allow the systeln to run fully

loaded for 20 minutes. Running oil level should be within view

in the crankcase sign glass. Stop compressor at the field power

supply disconnect and check the crankcase oil level. Add oil

only if necessary to bring the oil into view in the sight glass. If

oil is added, mn the system for an additional 10 minutes, then

stop and check oil level. If the level lemains low, check the

piping system for proper design for oil return; _dso check the

system for leaks.

If the initial check shows too much oil (too high in the sight

glass) lemove oil to proper level. See Preliminary Oil Charge

section for proper procedme for adding and removing oil.

When the above checks me complete, repeat the procedure

with the unit operating at minimum load conditions. Unload

the com_sor by disconnecting the field-control circuit lead

at TB2 _.

Reconnect the field-control circuit lead when checks are

complete.

Final Checks -- Ensure ;ill safety controls are operating,

control panel covers me on, and the service panels are in place.

Table 8 -- Maximum Refrigerant Charge

UNIT 38

AQ007

ARQ008,012

AQS016

R-22

(Ib) (kg)

27.0 12.2

34.2 15.5

62.0 28.1

SEQUENCE OF OPERATION

38AQ007 Units- When power is supplied to unit, the

transformer (TRAN) and crankcase heater (CCH) ale energized.

COOLING -- On a call for cooling, the thermostat completes

the following circuits: R-G. R-Y. and R-O. If the compressor

recycle delay of 3 minutes is complete, the compressor ;rod

outdoor fan start. The reversing valve is energized for cooling

and the indoor-fan motor starts.

When the thermostat is satisfied, the circuits are opened,

and the compressol: outdoor-fan motol: and indoor-fan motor

stop. The reversing valve is deenergized.

HEATING -- On a c;dl for heating, the thermostat completes

the following circuits: R-G and R-Y. If the compressor recycle

delay of 3 minutes is complete, the compressor and outdoor

fan st_u't. The indoor-fan motor will also staff.

If room temperature continues to fall, the thermostat

completes circuit R-W. If the optional electric heat package is

used, the heat relay is energized, and the electric heaters are

energized.

When the thermostat is satisfied, the circuits me opened,

and the compressor, outdoor-fan motor, heatel_, and indoor-fan

motor stop.

DEFROST -- Defrost board (DB) is a time and temperature

control, which includes a field-selectable time period between

checks for frost (30, 50, and 90 minutes). Electronic timer and

defrost cycle start only when contactor is energized and defrost

thermostat (DFT) is closed (below 28 F [-2.2 C]).

Defrost mode is identical to Cooling mode, except outdoor-

fan motor (OFM) stops and a bank of supplemental electric

heat turns on to wmm air supplying the conditioned space.

Defrost mode is terminated when the DFT reaches 65 F

(l 8.3 C).

AIR CIRCULATION -- When the fan switch is at FAN ON,

the indoor-air fans operate continuously to provide ventilation.

The thermostat operates the other components as described

above.

EMERGENCY HEAT CYCLE -- If the compressor is inoper-

ative due to a tripped safety device, the second stage of the

thermostat automatically energizes the indoor-air fan and the

electric resistance heaters (if equipped).

38ARQ008,012 Units--When power is supplied to

unit, the mmsformer (TRAN) is energized. The crankcase

heater is also energized.

COOLING--With the thermostat subbase in the cooling

position, and when the space temperature comes within 2° F

(1 ° C) of the cooling set point, the thermostat makes circuit

R-O. This energizes the reversing valve solenoid (RVS) and

places the unit in standby condition for cooling.

As the space temperature continues to rise, the second stage

of the thermostat makes, closing circuit R-Y. When compressor

time delay (5 _+2 minutes) is completed, a circuit is made to

contactor (C), staffing the compressor (COMP) and outdoor-

fan motor (OFM). Circuit R-G is made at the same time,

energizing the indoor-fan contactor (IFC) and starting the

indoor-fan motor (IFM) after one-second delay.

When the thermostat is satisfied, contacts open, deenergiz-

ing C. The COMR IFM, and OFM stop.

HEATING- On a call for heat, thermostat makes circuits

R-Y and R-G When compressor time delay (5 _+2 minutes) is

completed, a circuit is made to C, starting COMP and OFM.

Circuit R-G also energizes lFC and starts IFM after a 1-second

delay.

38AQS016 Units

HEATING -- Place therlnostat selector at HEAT and set tem-

perature selector above room ambient.

COOLING -- Place thermostat selector at COOL and set tem-

perature selector below room mnbient.

When thermostat c_dls for unit operation (either heating or

cooling), the indoor-fan motor starts immediately. The

outdoor-fan motors and compressor start within 3 seconds to

5 minutes depending on when unit was last shut off by thermo-

stat, because unit contains a compressor time delay circuit.

When first-stage cooling is required, thermostat (TCI) closes,

causing the heat pump to stmt with an unloaded compressol:

When TC2 closes, demanding additional cooling, the compres-

sor loads to full load operation.

During heating, compressor is always fully loaded. When

THI demands first-stage heating, the heat pump starts within

3 seconds to 5 minutes depending on when unit was last shut

off by thermostat, because unit contains a compressor time

delay circuit. (The defrost bomd has speed terminals to shorten

this cycle.) When TH2 of the thermostat closes, auxilimy heat

supply (electric strip heat) is energized in 1 or 2 stages depend-

ing on number of stages available and whether outdoor thermo-

stats are closed.

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Carrier 38AQ Specifications Page 21

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