Carrier 38AQ Specifications download pdf (Page 22)

Defrostis achievedby reversalfiomheatingto cooling

cycleanddeenergizationof outdoor-fanmotol.'s,allowinghot

refrigerantgastodefrostoutdoorcoil.Defrostisachievedwith

a timersetto initiatedefrostevery30,50,or 90minutes

(factorysetat30minutes).

Defrostisinitiatedwhenrefrigeranttemperatureleavingthe

outdoorcoilismeasuredbelow27F(2.8C),(typicallywhen

theoutdoorambienttemperatureis below45F [7.2C] as

sensedbythedefiostthermostat[DFTI).

Defrostis terminatedwhen:Therefrigeranttemperature

risesto65F(18.3C)(80F[26.7C]for38AQS016)attheDFT

locationontheliquidline;ortherefrigerantpressurerisesto

280psig(1931kPag)attheHPS2locationontheliquidline;or

thedefiosttimercompletesthe10-minntecycle.

Duplex Units

DUPLEX 38ARQ012 UNITS WITH 40RMQ024 (See

Fig. 12)

Cooling -- When the thermostat is set for cooling, and the

space temperature comes within 2° F (1 o C) of the cooling set

point, the thermostat completes the circuit from R to O and the

reversing valves in both units are energized. If the space tem-

perature continues to rise, the circuit from R to YI is complet-

ed. If the time delays and safeties are satisfied, the compressor

contactor closes, starting the compressor and outdoor-fan

motors of Heat Pump A. At the same time the circuit is

completed from R to G. starting the indoor-fan motor. If the

space temperature continues to rise, the circuit is completed

from R to Y2 and the Cooling mode is initiated in Heat Pump

B in a similar mannec

When the thermostat is satisfied, the contacts open, deener-

gizing first the Heat Pump B and then Heat Pump A.

Heating -- When the thermostat c_dls for heating, the circuit

fiom R to YI is completed. If the time delays and safeties are

satisfied, the compressor contactor closes, sttuting the com-

pressor and outdoor-fan motors of Heat Pump A and Heat

Pump B. At the same time the circuit is completed from R to G.

st_uting the indoor-fan motol: If the second stage of heating is

required, the circuit from R to W2 will be completed and the

electric resistance heaters will be energized.

When the thermostat is satisfied, the contacts open, deener-

gizing Heat Pump A and Heat Pump B.

DUPLEX 38AQS016 AND 38ARQ012 UNITS WITH

40RMQ028 (See Fig. 13)

Cooling -- When the thermostat calls for cooling, the circuit

from R to YI is completed. If the time delays and safeties are

satisfied, the compressor contactor closes, sttuting the com-

pressor and outdoor-fan motors of Heat Pump A (38AQS016).

At the same time the circuit is completed form R to G. stmling

the indoor-fan motol: If the space temperature continues to rise,

the circuit is completed from R to Y2 and the Cooling mode is

initiated in Heat Pump B (38ARQ012).

When the thermostat is satisfied, the contacts open, deener-

gizing first the Heat Pump B and then Heat Pump A.

Heating -- When the thermostat c_dls for heating, the circuit

from R to WI is completed. If the time delays and safeties are

satisfied, the compressor contactor closes, st_uting the com-

plessor and outdoor-fan motors of Heat Pump A and Heat

Pump B. At the same time the circuit is completed from R to G.

st_uting the indoor-fan motol: If the second stage of heating is

required, the circuit from R to W2 will be completed and the

electric lesistance heaters will be energized.

When the thermostat is satisfied, the contacts open, deener-

gizing Heat Pump A and Heat Pump B.

SAFETIES- The high-plessure switch, loss-of-charge

switch, oil pressure safety switch, and compressor overtemper-

ature safety are located in a CLO that prevents heat pump

operation if these safety devices are activated. The lockout

system can be reset by adjusting the thermostat to open the

contacts (down for Heating mode, up for Cooling mode), deen-

ergizing the CLO. Compressor overcurrent protection is

achieved with a circuit breaker which requires manual reset-

ting at the outdoor unit control box (38AQS only).

The 38AQS unit is equipped with an oil pressure safety

switch that protects the compressor if oil pressure does not de-

velop on start-up or is lost during operation. The oil pressure

switch is of the manual reset type and therefore must be reset at

the outdoor unit. DO NOT RESET MORE THAN ONCE.

If oil pressure switch trips, determine cause and correct. DO

NOT JUMPER OIL PRESSURE SAFETY SWITCH.

To reset the oil pressure switch:

1. Disconnect power to the unit.

2. Press the RESET button on the oil pressure switch.

3. Reconnect power to the unit.

Unit is equipped with a no-dump reversing valve circuit.

When unit is in Cooling mode, reversing valve remains in cool-

ing position until a call for heating is requested by themlostat.

When unit is in Heating mode, reversing valve remains in heat-

ing position until there is a call for cooling.

CHECK OPERATION -- Ensure operation of all safety con-

trois. Replace zfll service panels. Be sure that control panel

cover is dosed tigh@

Restart --Manu_fl reset of the 24-v control circuit is

necessa q if unit shutdown is caused by automatic reset devices

(including IP [internal compressor overcurrent protectionl,

HPS [high-pressure switchl, LCS [loss-of-charge switchl), or if

shutdown is caused by manual reset devices (including OPS

[oil pressure switchl and compressor circuit breaker protec-

tion). To restart the unit when IR HPS, or LCS has tripped (@

Wr device has reset automati_zd@), open and then close the

thermostat contacts. Opening and then closing thermostat con-

tacts interrupts and restores 24-v power to the CLO, which

resets the circuit.

It is necessary to manu_dly reset the compressor cimuit

breaker and OPS at the unit if either of these safeties should

shut down the unit.

IMPORTANT: If OPS trips, it must be reset fi_t before

making and b_eaking the thermostat contacts to reset

CLO. If this procedure is not followed, the CLO cannot

_eset.

Causes of Complete Unit Shutdown:

• interruption of supplied power

• open compressor overtemperature protection (IP)

• compressor electrical overload protection (CB)

• open high-pressure or loss-of-charge safety switches

• open oil pressure switch

• open crankcase heater lockout (CLO2)

• open control circuit fuse (FUI or FU2)

• open discharge gas thermostat (38ARQ only)

SERVICE

Compressor Removal -- See Tables IA-ID for com-

pressor information. Follow safety codes and wear safety

glasses and work gloves.

1. Shut off power to unit. Remove unit access panel.

2. Recover refrigerant from system using refrigerant recovery

methods described in C;urier Training booklet GTAC |I,

Module 5, and in accordance with loc:d and national

stan&_rds.

3. Disconnect compressor wiring at compressor termimd

box.

4. Disconnect refrigerant lines from compressol:

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Carrier 38AQ Specifications Page 22

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