Carrier specifications Stage Sequence 48/50AJ,AW020-027, Stage Sequence 48/50AJ,AW030-060

then Lo Cool Mode mechanical stages = 2 and Hi Cool Mode mechanical stages = 2.

5.If the economizer position is greater than Configuration →ECON→EC.MX – 5% for more than 8 minutes but less than 11.5 minutes and mechanical cooling has started then:

Lo Cool Mode mechanical stages = 2 Hi Cool Mode mechanical stages = 3

6.If the economizer position is greater than Configuration →ECON→EC.MX – 5% for more than 11.5 minutes and mechanical cooling has started then:

Lo Cool Mode mechanical stages = 2

Hi Cool Mode mechanical stages = 3 (for 020 to 027 units only)

Hi Cool Mode mechanical stages = 4 (for 030 to 060 units only)

NOTE: If some compressors are not available due to being faulted, the Hi Cool Mode number of compressors are affected before the Lo Cool Mode number of compressors. For exam- ple, if a 4 compressor unit has one compressor faulted, and the economizer is not active, then an HVAC mode Hi Cool requested number of compressors is changed from 4 to 3. If another compressor faults, then both Lo Cool and Hi Cool requested number of compressors are set to 2. In addition, compressors cannot be brought on faster than one every 30 seconds. If the control needs to bring on 2 compressors at once, the first compressor will come on followed by the second compressor 30 seconds later.

Staging of compressors is shown in Tables 49-60.

EDT Low Override — There is an override if EDT drops too low based on an alert limit that will lock out cooling. If the supply air/evaporator discharge temperature (EDT) falls below the alert limit (Configuration→ALLM→SA.L.O) cooling will be inhibited. There is a 20-minute hold off on starting cooling again once the following statement is true: EDT minus (Run Status→COOL→SUMZ→ADD.R) has risen above SA.L.O.

The variable ADD.R is one of the SumZ cooling algorithm control variables dedicated mainly for multi-stage control.

2-Stage Control and the Economizer — The 2-stage logic will first check for the availability of the economizer. If free cooling can be used, then the control will first attempt to use the free cooling.

If no mechanical cooling is active, and the economizer is active, the economizer will first attempt to control to a cooling control point of either the supply air set point high (SA.HI) or supply air set point low (SA.LO) plus any reset applied, depending on whether High Cool or Low Cool mode is in ef- fect, respectively.

If one stage of mechanical cooling is on, and the economiz- er is active, then the economizer will attempt to control to 53 F. Also If HVAC mode = LOW COOL, the second stage of mechanical cooling will be locked out.

If the set point cannot be satisfied or the economizer is not active, then cooling will be brought on one stage at a time when the evaporator discharge temperature (EDT) is greater the 1.5° F above the current cooling control point. A start-up time delay of 10 minutes and steady state delay after a com- pressor is energized of 5 minutes is enforced.

If both circuits of mechanical cooling are running, then the economizer will attempt to control to 48 F. If the economizer is active and the outside-air temperature (OAT) is less than the cooling control point + 0.5 F, the compressors will be locked off. When mechanical cooling is on, the control may also use the economizer to trim the leaving-air temperature to prevent unnecessary cycles of the compressor stages.

See the Economizer Integration with Mechanical Cooling section on page 50 for more information on the holding off of mechanical cooling as well as the economizer control point.

Table 49 — 2-Stage Sequence —

48/50AJ,AW020-027

STAGE		SEQUENCE 1				SEQUENCE 2
	0		1	2	0		1	2
	Thermostat Inputs				Thermostat Inputs
Y1	OPEN		CLOSED	CLOSED	OPEN		CLOSED	CLOSED
Y2	OPEN		OPEN	CLOSED	OPEN		OPEN	CLOSED
COMP	Compressor Status				Compressor Status
A1	OFF		ON	ON	OFF		OFF	ON
A2	OFF		OFF	ON	OFF		ON	ON
B1	OFF		OFF	ON	OFF		OFF	ON
UNIT			Unit Capacity			Unit Capacity
020	0%		33%	100%	0%		33%	100%
025	0%		30%	100%	0%		30%	100%
027	0%		33%	100%	0%		33%	100%

Table 50 — 2-Stage Sequence —

48/50AJ,AW030-060

STAGE		SEQUENCE 1				SEQUENCE 2
	0		1	2	0		1	2
	Thermostat Inputs				Thermostat Inputs
Y1	OPEN		CLOSED	CLOSED	OPEN		CLOSED	CLOSED
Y2	OPEN		OPEN	CLOSED	OPEN		OPEN	CLOSED
COMP	Compressor Status				Compressor Status
A1	OFF		ON	ON	OFF		ON	ON
A2	OFF		ON	ON	OFF		ON	ON
B1	OFF		OFF	ON	OFF		OFF	ON
B2	OFF		OFF	ON	OFF		OFF	ON
UNIT		Unit Capacity				Unit Capacity
030	0%		45%	100%	0%		45%	100%
035,036	0%		48%	100%	0%		48%	100%
040,041	0%		43%	100%	0%		43%	100%
050	0%		45%	100%	0%		45%	100%
051,060	0%		50%	100%	0%		50%	100%

Table 51 — Staging Sequence without Hot Gas Bypass — 48/50AK,AY020-027 and Multi-Stage 48/50AJ,AW020-027

STAGE				SEQUENCE 1						SEQUENCE 2
	0	1		2	3	4	0	1		2	3	4
COMP			Compressor Status						Compressor Status
A1	OFF	ON		ON	OFF	ON	OFF	OFF		ON	ON	ON
A2	OFF	OFF		ON	ON	ON	OFF	ON		ON	OFF	ON
B1	OFF	OFF		OFF	ON	ON	OFF	OFF		OFF	ON	ON
UNIT			Unit Capacity 48/50A						Unit Capacity 48/50A
020	0%	33%		67%	67%	100%	0%	33%		67%	67%	100%
025	0%	30%		65%	70%	100%	0%	35%		65%	65%	100%
027	0%	33%		67%	67%	100%	0%	33%		67%	67%	100%

43