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

5.If the economizer position is greater than Configuration ECONEC.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 ECONEC.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 (ConfigurationALLMSA.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 StatusCOOLSUMZADD.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

Page 43
Image 43
Carrier specifications Stage Sequence 48/50AJ,AW020-027, Stage Sequence 48/50AJ,AW030-060