Carrier 48/50AJ Run Status Mode Trip Helper, R.Pct = Mat – Edt/ C.Cap, Y.MIN = -SUB.R*0.4375

COOLING MODE DIAGNOSTIC HELP — To quickly de- termine the current trip points for the cooling modes, the Run Status sub-menu at the local display allows the user to view the calculated start and stop points for both the cooling and heating trip points. The following sub-menu can be found at the local display under Run Status→TRIP. See Table 61.

The controlling temperature is “TEMP” and is in the middle of the table for easy reference. The HVAC mode can also be viewed at the bottom of the table.

SUMZ COOLING ALGORITHM — The SumZ cooling algo- rithm is an adaptive PID which is used by the control whenever more than 2 stages of cooling are present (C.TYP = 1,2,3, and 5). This section will describe its operation and define its param- eters. It is generally not necessary to modify parameters in this section. The information is presented primarily for reference and may be helpful for troubleshooting complex operational problems.

The only configuration parameter for the SumZ algorithm is located at the local display under Configuration →COOL→Z.GN. See Table 47.

Table 61 — Run Status Mode Trip Helper

ITEM	EXPANSION	UNITS	CCN
			POINT
TRIP	MODE TRIP HELPER
UN.C.S	Unoccup. Cool Mode Start	dF	UCCLSTRT
UN.C.E	Unoccup. Cool Mode End	dF	UCCL_END
OC.C.S	Occupied Cool Mode Start	dF	OCCLSTRT
OC.C.E	Occupied Cool Mode End	dF	OCCL_END
TEMP	Ctl.Temp RAT,SPT or Zone	dF	CTRLTEMP
OC.H.E	Occupied Heat Mode End	dF	OCHT_END
OC.H.S	Occupied Heat Mode Start	dF	OCHTSTRT
UN.H.E	Unoccup. Heat Mode End	dF	UCHT_END
UN.H.S	Unoccup. Heat Mode Start	dF	UCHTSTRT
HVAC	the current HVAC MODE		String

Capacity Threshold Adjust (Z.GN) — This configuration is used on units using the “SumZ” algorithm for cooling capacity control (Configuration→UNIT→C.TYP = 1, 2, 3 and 5). It affects the cycling rate of the cooling stages by raising or lowering the threshold that capacity must overcome in order to add or subtract a stage of cooling.

The cooling algorithm’s run-time variables are located at the local display under Run Status→COOL. See Table 62. Current Running Capacity (C.CAP) — This variable repre- sents the amount of capacity in percent that is currently running.

Current Cool Stage (CUR.S) — This variable represents the cool stage currently running.

Requested Cool Stage (REQ.S) — This variable represents the cool stage currently requested by the control.

Maximum Cool Stages (MAX.S) — This variable is the max- imum number of cooling stages the control is configured for and capable of controlling.

Active Demand Limit (DEM.L) — If demand limit is active, this variable will represent the amount of capacity that the control is currently limited to.

Capacity Load Factor (SMZ) — This factor builds up or down over time (–100 to +100) and is used as the means of adding or subtracting a cooling stage during run time. It is a normalized representation of the relationship between “Sum” and “Z”.

Next Stage EDT Decrease (ADD.R) — This variable repre- sents (if adding a stage of cooling) how much the temperature

should drop in degrees depending on the R.PCT calculation and exactly how much additional capacity is to be added.

ADD.R = R.PCT * (C.CAP — capacity after adding a cooling stage)

For example: If R.PCT = 0.2 and the control would be adding 20% cooling capacity by taking the next step up, 0.2 times 20 = 4 F (ADD.R).

Next Stage EDT Increase (SUB.R) — This variable repre- sents (if subtracting a stage of cooling) how much the temperature should rise in degrees depending on the R.PCT calculation and exactly how much capacity is to be subtracted. SUB.R = R.PCT * (C.CAP — capacity after subtracting a cooling stage)

For Example: If R.PCT = 0.2 and the control would be sub- tracting 30% capacity by taking the next step down, 0.2 times –30 = –6 F (SUB.R)

Rise Per Percent Capacity (R.PCT) — This is a real time cal- culation that represents the amount of degrees of drop/rise across the evaporator coil versus percent of current running capacity.

R.PCT = (MAT – EDT)/ C.CAP

Cap Deadband Subtracting (Y.MIN) — This is a control vari- able used for Low Temp Override (L.TMP) and Slow Change Override (SLOW).

Y.MIN = -SUB.R*0.4375

Cap Deadband Adding (Y.PLU) — This is a control variable used for High Temp Override (H.TMP) and Slow Change Override (SLOW).

Y.PLU = -ADD.R*0.4375

Cap Threshold Subtracting (Z.MIN) — This parameter is used in the calculation of SumZ and is calculated as follows:

Z.MIN = Configuration→COOL→Z.GN * (–10 + (4*

(–SUB.R))) * 0.6

Cap Threshold Adding (Z.PLU) — This parameter is used in the calculation of SumZ and is calculated as follows:

Z.PLU = Configuration→COOL→Z.GN * (10 + (4*

(–ADD.R))) * 0.6

High Temp Cap Override (H.TMP) — If stages of mechani- cal cooling are on and the error is greater than twice Y.PLU, and the rate of change of error is greater than 0.5° F per minute, then a stage of mechanical cooling will be added every 30 sec- onds. This override is intended to react to situations where the load rapidly increases.

Low Temp Cap Override (L.TMP) — If the error is less than twice Y.MIN, and the rate of change of error is less than –0.5° F per minute, then a mechanical stage will be removed every 30 seconds. This override is intended to quickly react to situations where the load is rapidly reduced.

Pull Down Cap Override (PULL) — If the error from set point is above 4° F, and the rate of change is less than –1° F per minute, then pulldown is in effect, and “SUM” is set to 0. This keeps mechanical cooling stages from being added when the error is very large, but there is no load in the space. Pulldown for units is expected to rarely occur, but is included for the rare situation when it is needed. Most likely pulldown will occur when mechanical cooling first becomes available shortly after the control goes into an occupied mode (after a warm unoccu- pied mode).

46