Carrier 38AUQ Heat Pump Controls, Crankcase Heater, Commercial Defrost Control, Control Circuit

Heat Pump Controls

Compressor Protection

Compressor Overcurrent

The compressor has internal limbered motor protection.

Compressor Overtemperature

The compressor has an internal protector to protect it against excessively high discharge gas temperatures.

High Pressure Switch

The system is provided with a high pressure switch mount- ed on the discharge line. The switch is stem-mounted and brazed into the discharge tube. Trip setting is 630 ± 10 psig (4344 ± 69 kPa) when hot. Reset is automatic at 505 ± 20 psig (3482 ± 140 kPa).

Loss of Charge Switch

The system is protected against a loss of charge and low evaporator coil loading condition by a loss of charge switch located on the liquid line and a freeze protection thermostat on the indoor coil. The switch is stem-mounted. Loss of Charge Switch trip setting is 27 psig ± 3 psig (186 ±21 kPa). Reset is automatic at 44 ±5 psig (303 ± 35 kPa).

Outdoor Fan Motor Protection

The outdoor fan motor is internally protected against overtem- perature.

Control Circuit, 24-V

The control circuit is protected against overcurrent conditions by a circuit breaker mounted on control transformer TRAN. Reset is manual.

Crankcase Heater

The heater prevents refrigerant migration and compressor oil dilution during shutdown whenever compressor is not operat- ing. The heater is wired to cycle with the compressor; the heat- er is off when compressor is running, and on when compressor is off.

The crankcase heater will operate as long as the power circuit is energized.

IMPORTANT: Never open any switch or disconnect that energizes the crankcase heater unless unit is being serviced or is to be shut down for a prolonged period. After a pro- longed shutdown on a service job, energize the crankcase heater for 24 hours before starting the compressor.

Commercial Defrost Control

The Commercial Defrost Control Board (DFB) coordinates thermostat demands for supply fan control, 1 or 2 stage cooling, 1 or 2 stage heating, emergency heating and defrost control with unit operating sequences. See Fig. 22 for board arrangement.

The DFB is located in the 38AUQ's main control box (see Fig. 21). All connections are factory-wired. Refer to Table 12 for details of DFB Inputs and Outputs.

Table 12 —38AUQ Defrost Board I/O and Jumper Configurations

Inputs

Point Name	Type of I/O	Connection Pin Number	Unit Connection	Note
G Fan	DI, 24-vac	P2-3		Not used
Y1 Cool 1	DI, 24-vac	P2-5	TB-Y1
Wi Heat 1	DI, 24-vac	P2-7	TB-W1
R Power	24-vac	P3-1	TRAN2
C Common	24-vac, ground	P3-3	TRAN2
DFT1 Defrost Switch	DI, 24-vac	DFT-1 to DFT-1	DFB

Outputs

Point Name	Type of I/O	Connection Pin Number	Unit Connection	Note
OF OD Fan	DO, 24-vac	OF	OFR
RVS1	DO, 24-vac	P3-7 to P3-5	RVS1	Energize in COOL
RVS2	DO, 24-vac	P3-6 to P3-4	RVS2	Energize in COOL
COMP 1	DO, 24-vac	P3-10	CADM1-Y
HEAT 2	DO, 24-vac	E-HEAT	HC-1 (TB4-1)

Configuration

Point Name	Type of I/O	Connection Pin Number	Unit Connection	Note
Select Jumper	24-vac	P1-1
1 Compressor	24-vac	P1-2

Speed-Up Configuration

Point Name	Type of I/O	Connection Pin Number	Unit Connection	Note
Speed-Up Jumper		JMP17
Speed-Up Jumper		JMP18

Jumper for 1-3 secs: Factory Test, defrost runs for 12 seconds or less

Jumper for 5-20 secs: Forced Defrost, defrost runs for 30 secs if DFT2 is open

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