Manual Carrier 48 50PM C16-28 (page 24 of 188) (English)

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Free Cool PreOcc Time (FC.TM)

FC.TM is the configuration that determines how many minutes

before occupancy that free cooling can occur when set for

Preoccupancy (UEFC = 2).

Free Cool Low Temp Limit (FC.LO)

Unoccupied free cooling cannot occur if the Outdoor Air

Temperature (Temperature→ AIR.T→ OAT) is less than FC.LO.

Power Exhaust

To enable power exhaust, Configuration→ECON→PE.EN must

be set to ENBL. If power exhaust is enabled, Power Exhaust 1 will

turn on when the economizer position is greater than the value of

Configuration→ECON→PE.1. If power exhaust is enabled,

Power Exhaust 2 will turn on when the economizer position is

greater than the value of Configuration→ECON→PE.2. There are

small time delays to ensure that rapid cycling does not occur.

Optional Humidi−MiZert Dehumidification

System

Units with the factory−equipped Humidi−MiZer option are capable

of providing multiple modes of improved dehumidification as a

variation of the normal cooling cycle. The Humidi−MiZer option

includes additional valves in the liquid line and discharge line of

each refrigerant circuit, a small reheat condenser coil downstream

of the evaporator, and Motormaster variable−speed control of

some or all outdoor fans. The Humidi−MiZer Equipped

(Configuration→HMZR→REHT) configuration is factory set to

Yes for Humidi−MiZer equipped units. This enables

Humidi−MiZer operating modes and service test.

NOTE: If the unit is a Humidi−MiZer unit, this configuration

must always be set to yes. The Humidi−MiZer option does affect

the base unit wiring.

Humidi−MiZer operation requires installation and configuration of

either a space relative humidity sensor or a relative humidity switch

input. Space Humidity Switch (Configuration→UNIT→RH.SW)

set to 1 for use of a normally open switch or 2 for normally closed

switch. The switch is wired to field connection terminal board

terminals labeled HUMDISTAT. Set RH Sensor on OAQ Input

(Configuration→UNIT→RH.S) to Yes for use of a 4 to 20 mA

output RH sensor wired to field connection terminal board (TB)

terminals 1 and 4 (for loop powered). RH Sensor Value at 4ma

(Configuration→AIR.Q→H.4M) sets the % display for a 4mA

input from the relative humidity sensor. RH Sensor Value at 20ma

(Configuration→AIR.Q→H.20M) sets the % display for a 20mA

input from the relative humidity sensor.

Dehumidification Demand

When using a humidistat or switch input, the demand for

dehumidification is seen as Space Humidity Switch (Inputs

→GEN.I→HUM) being Low or High. A low value means

humidity level is good and a high value means that

dehumidification is needed. When using an RH sensor, the demand

is based on the Space Humidity Sensor (Inputs→AIR.Q→SP.RH)

value compared to the Space RH Occupied Setpoint

(Setpoints→RH.SP) during the occupied period and Space RH

Unoccupied Setpoint (Setpoints → RH.UN) during unoccupied

periods. If the Space Humidity Sensor (SP.RH) value is above the

Space RH Setpoint (RH.SP), then dehumidification is needed. If

the Space Humidity Sensor (SP.RH) value is below the Space RH

Setpoint (RH.SP) minus the Space RH Deadband

(Setpoints→RH.DB), then dehumidification is no longer needed.

If the unit is configured for space sensor control

(Configuration→UNIT →U.CTL = 3), then the setpoint Reheat

Heat SP Deadband (Setpoints→RH.HB) applies. This

configuration sets the offset above the heating set point at which a

unit in Reheat2 mode will turn off. This is a protection against over

cooling the space and causing a heat demand.

NOTE: When there is a dehumidification demand, the economizer

damper position is limited to it’s minimum damper position

(Operating Mode→ECON→EC.MP).

Reheat Modes

Dehumidification (reheat) is a cooling mode function. Refer to

Cooling Operation for cooling mode control. With Humidi−MiZer

units there are three additional HVAC Mode (HVAC) expanded

texts available for the user: Reheat1, Reheat2, and

Reheat1/Reheat2. Selection of the reheat mode for each refrigerant

circuit is determined by the dehumidification demand and the

cooling demand. Table 10 shows the corresponding circuit mode

and output status for the different demand combinations. Units

with multiple circuits can operate with a combination of Reheat1

and Reheat2 circuits, as determined by the amount of space cooling

demand. See Appendix B for complete tables of unit operation

response to thermostat and humidity inputs.

NOTE: Compressor staging control for Humidi−MiZer units

requires that circuit A always operates when either circuits B or C

are on. This applies to normal operation, service test, and for

control alarm responses. This operation difference is required due

to the fact that the Motormaster outdoor fan control senses circuit

A only.

Operation of the revised refrigerant circuit for each mode is

described below.

NOTE: x = refrigerant circuit A, B, or C

Normal Cooling

For 48/50PG03−16 units, refrigerant flows from the outdoor

condenser through the normally open Cooling Valve (CV.x) to the

expansion device. Reheat1 Valve (RH1.x) and Reheat2 Valve

(RH2.x) are closed. (See Fig. 9.)

For 48/50PG20−28 and 48/50PM16−28 units, refrigerant flows

from the outdoor condenser through the de−energized 3−way valve

(RH.x) to the expansion device. Reheat2 Valve (RH2.x) is closed.

(See Fig. 12.)

Reheat 1 (Subcooling Mode)

This mode increases latent cooling and decreases sensible cooling

compared to normal cooling.

For 48/50PG03−16 units, refrigerant flows from the outdoor

condenser, through the normally open Reheat 1 Valve (RH1.x),

and through the reheat condenser coil to the expansion device.

Cooling Valve (CV.x) and Reheat2 Valve (RH2.x) are closed. (See

Fig. 10.)

For 48/50PG20−28 and 48/50PM16−28 units, refrigerant flows

from the outdoor condenser, through the energized 3−way Valve

(RH1.x), and through the reheat condenser coil to the expansion

device. Cooling Reheat2 Valve (RH2.x) is closed. (See Fig. 13.)

Reheat 2 (Hot Gas Reheat Mode)

This mode provides maximum latent cooling with little to no

sensible capacity. This mode can operate to provide

dehumidification when there is no cooling demand. Similar to

Reheat 1 mode, refrigerant flows from the outdoor condenser,

through the normally open Reheat 1 Valve (RH1.x), or through the

energized 3−way valve (RH.1x), and through the reheat condenser

coil to the expansion device. Reheat2 Valve (RH2.x) is open which

provides some compressor discharge gas to the reheat condenser to

further increase the reheat of the evaporator air stream (See Fig. 11

or 14 based on unit and size).

NOTE: Humidi−MiZer outdoor fan configurations are dependent

on the specific unit and should not be changed. The configurations

are provided in case a field replacement of a control board occurs

and the settings need to be checked or manually configured. See

Appendix A for range and defaults.

48/50PG and PM

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Carrier 48 50PM C16-28 Manual

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