Carrier Compressor and Condensing Unit Service, Protection Devices, Capacity Control System

SERVICE

Protection Devices

HIGH-PRESSURE SWITCH — Check by throttling con- denser water or blocking airflow on air-cooled units, allowing head pressure to rise gradually. Check discharge pressure constantly throughout procedure. Compressor should shut off within 10 psi of values shown in Table 4.

LOW-PRESSURE SWITCH — Check by slowly closing suction shutoff valve or by completely closing liquid line shutoff valve. A decrease of suction pressure will follow. Compressor should shut off within 4 psi of values shown in Table 4.

OIL PRESSURE SWITCH (OPS) — The oil pressure switch protects against damage from loss of oil or loss of oil pressure during unit start-up. If the oil pressure differential sensed by the OPS is 6 psig or less on unit start-up, the switch remains closed and the OPS heater is energized.

The switch time delay is approximately 45 seconds. If after

45 seconds the oil pressure differential sensed by the OPS is less than 11 psig, the heater remains energized. The OPS temperature actuated switch then opens and the compressor is deenergized. If the differential reaches 11 psig, the OPS opens and deenergizes the heater and the system operates normally. See Table 4.

IMPORTANT: If the oil pressure switch causes unit lock- out, determine and correct the cause of the lockout (such as loss of compressor oil or flooded compressor) before restarting the unit. Failure to correct the cause of OPS lockout may constitute abuse. Equipment failure due to abuse is not covered by warranty.

To restart the unit, push the OPS reset button and then push the control circuit switch on the unit control box to OFF and then to ON.

Table 4 — Factory Switch Settings

	PRESSURE CHANGE AFFECTING
SWITCH TYPE	SWITCH POSITION (psig)
	Closed		Open
High Pressure	210	(±10)	290	(±10)
Low Pressure	70	(±4)	60	(±4)
Oil Pressure		6	11

NOTES:

1.Values for the high- and low-pressure switches based on R-22. For other refrigerants, reset to pressure corresponding to satura- tion temperatures indicated by the listed pressures.

2.Values for oil pressure are above operating suction pressure (pressure differential between suction and discharge pressures of oil pump).

TIME GUARD® CONTROL — The Time Guard control protects against short cycling. See Start Compressor.

CRANKCASE HEATER — The crankcase heater prevents absorption of liquid refrigerant by oil in crankcase during brief or extended shutdown periods. Source of 115-volt power is the auxiliary control power, independent of the main unit power. This assures compressor protection even when main unit power disconnect switch is off.

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

Compressor Thermal Protection — A discharge temperature sensor, installed in one cylinder head, detects an overtemperature condition. If the discharge temperature

exceeds 295 ± 5 F, the sensor contacts open and the compressor shuts down. The sensor reset temperature is 235 F minimum. See Fig. 8 for control circuit connections.

Capacity Control System

CAPACITY CONTROL VALVE (Fig. 9) — Valve is con- trolled by suction pressure and actuated by discharge pressure. Each valve controls 2 cylinders. On start-up, controlled cylinders do not load up until differential between suction and discharge pressures is approximately 25 psi. See Table 5.

IMPORTANT: Do not use automatic pumpdown control on 06E,07E units equipped with unloader valves. Use single pumpout or solenoid drop (minimum protection) control.

CAPACITY CONTROL VALVE ADJUSTMENTS

Control Set Point (Cylinder Load Point) — Adjustable from 0 to 86 psig. Pressure differential between cylinder load-up point and cylinder unload point is adjustable from 6 psi to 16 psi.

		CR
	4	6	RED	C1 C2 C2	YEL	C2 C1
	BLU
TIMER	B2			DTS
	B	ORN			BLU
CONTACTS
	B1				TB2	6

LEGEND

C— Compressor Contactor CR — Control Relay

DTS — Discharge Temperature Sensor TB — Terminal Block

•Splice (in compressor junction box)

Fig. 8 — Discharge Temperature Sensor (DTS)

CONTROL

SET POINT

ADJUSTMENT

NUT

VALVE BODY

SEALING CAP

(COVERS PRESSURE DIFFERENTIAL

ADJUSTMENT SCREW)

Fig. 9 — Capacity Control Valve

9