Sterling 30RA010-055 Operating Envelope for, R-22Maneurop Compressor, 30RA Condenser Fan Sequence

Head Pressure Control — The Main Base Board (MBB) controls the condenser fans to maintain the lowest condensing temperature possible, and thus the highest unit efficiency. The MBB uses the saturated condensing tempera- ture input from the discharge pressure transducer to control the fans. Head pressure control is maintained through a calculated set point which is automatically adjusted based on actual

	160								149				154
	140
	120
(F)	105
SCT	100
	80												78
	60
	47.5
	40		0	5	10	15	20			35	40	45	50	55
	-10	-5						25	30
						R-22 SST (F)

LEGEND

SCT — Saturated Condensing Temperature

SST — Saturated Suction Temperature

Fig. 13 — Operating Envelope for

R-22 Maneurop Compressor

saturated condensing and saturated suction temperatures so that the compressor(s) is (are) always operating within the manufacturer's specified envelope (see Fig. 13). The control will automatically reduce the unit capacity as the saturated condensing temperature approaches an upper limit. The control will indicate through an alert that a high ambient unloading mode is in effect. If the saturated condensing temperature in a circuit exceeds the calculated maximum, the circuit will be stopped. For these reasons, there are no head pressure control methods or set points to enter. If the saturated condensing temperature in a circuit is greater than or equal to 95 F (35 C) at start-up, all available condenser fans will be started to prevent excessive discharge pressure during pull-down. The control will turn off a fan stage when the condensing temperature has been below the calculated head pressure set point by 35 F (19.4 C) for more than 2 minutes. Fan sequences are shown in Fig. 14.

MOTORMASTER® V OPTION — For low-ambient opera- tion, the lead fan on a circuit can be equipped with the Motormaster V head pressure controller option or accessory. The control will automatically raise the head pressure set point by 5 F (2.8 C) when Motormaster control is configured. The controller is energized with the first fan stage and adjusts fan speed to maintain a liquid pressure of 135 psig (931 kPa). For sizes 010-018 and Circuit B of sizes 032-040, the two-speed fan is wired for high speed operation and the Motormaster V controller adjusts fan speed. For size 022-030, 042-055 and circuit A of the 032-040 sizes, the lead fan (A1 or B1) in the circuit is controlled. Refer to Fig. 14 for condenser fan staging information. Refer to Fig. 15 for typical pressure transducer location.

FAN ARRANGEMENT				FAN NO.	FAN RELAY	NORMAL CONTROL
	30RAN010-018			1	FC-LS	Energize Fan at
CONTROL						Low Speed
BOX			1	1	FC-HS	Energize Fan at
END
						High Speed
	30RAN022-030			1	FC-A1	First Stage
CONTROL						Condenser Fan
BOX		1	2	2	FC-A2	Second Stage
END
						Condenser Fan
	30RAN032-040			1	FC-A1	On with Compressor A1
						and/or Compressor A2
CONTROL
				2	FC-A2	First Stage Condenser
BOX		1	2
						Fan, Circuit A
END
				3	FC-LS	Low Speed, Fan on
		3				w/Compressor B1
				3	FC-HS	Energize Fan at High Speed,
						Circuit B
	30RAN042-055			1	FC-A1	On with Compressor A1
						and/or Compressor A2
CONTROL
				2	FC-A2	First Stage Condenser Fan,
BOX
		1	2			Circuit A
END
				3	FC-B1	On with Compressor B1
		3	4			and/or Compressor B2
				4	FC-B2	First Stage Condenser Fan,
						Circuit B

Fig. 14 — 30RA Condenser Fan Sequence

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