Carrier Access Thermidistat ÐHumidification Selections, Additional Humidify Comments

Table 4ÐHumidification Selections

SELECTION	MODE DISPLAY	FAN DISPLAY	HUMIDIFY SET POINT
			DISPLAY
Normal Humidify	Blank	Blank	Humidify Set Point Value
Fan Humidify	Blank	FAN	Humidify Set Point Value
Auto Humidify	AUTO	Blank	Humidify Set Point Value
Auto and Fan	AUTO	FAN	Humidify Set Point Value
Humidify Off	Blank	Blank	OF

4.Auto and Fan Humidify

The 2 choices of AUTO and FAN can be selected together. This provides both functions simultaneously.

5.Humidify Off

The humidify function can be turned off completely. This does not require changing existing set points.

To Select Humidification (Between NORMAL, FAN, AUTO, FAN and AUTO, or OFF) (See Table 4.)

Press HUMIDITY button to bring up humidity select screen. It is indicated by "hu" or "dhu" in clock display. Successive presses will change between "hu" and "dhu" in clock display. Select "hu" for humidity functions. The large display shows actual humidity level. The smaller display (in heat set point location) shows humidity set point (Humidify Set Point) or OF (off). When Humidity Set Point value is displayed, its value can be changed with up and down buttons. Successive presses of MODE button will move between 5 choices described above and each will be indicated as shown in Table 4.

To exit humidity select screen, press END button.

Additional Humidify Comments

The humidifier is actually turned on when humidity is 2 percent below set point and turned off when it reaches 2 percent above set point. This built-in hysteresis prevents humidify output from toggling on and off when humidity level is near set point.

The vacation mode provides some additional humidification func- tions. These are specially designed to provide protection for an unoccupied home while simultaneously minimizing energy use. Refer to "Vacation" section for additional information.

DEHUMIDIFICATION

Dehumidification is done only during cooling. Depending on type of equipment used, compressor speed, blower speed, set point adjustment, and equipment cycling are modified to provide added dehumidification. A dehumidification set point (separate from humidification set point) is available to the homeowner. It can range from 50 to 90 percent relative humidity. When actual humidity is higher than set point, a dehumidification demand exists. The Thermidistat Control responds by activating its dehu- midify output. It may also control the compressor and blower, depending on equipment type and dehumidify selection choice. The 3 available selections are described below.

The amount of extra dehumidification available is very dependent on the type of equipment in the home. Without a variable-speed blower, the system's ability to adjust dehumidification is very limited.

1.Normal Dehumidify Operation

When normal dehumidify is selected, the compressor will not turn on without a cooling demand. If dehumidify demand exists while cooling, dehumidify output will also be active (24vac removed). This output commands variable-speed blowers to reduce their airflow, which improves water re- moval from the cooled air.

2.Cool to Dehumidify

The cool to dehumidify selection tells the system to operate the compressor, within limits, when there is a dehumidify demand even if there is no cooling demand. The limits are that the system may overcool up to 3°, but no more, while attempting to satisfy a dehumidify demand. Within this 3° range, there is an additional balance between overcooling and humidity satisfaction. When overcooling must occur, the dehumidify set point is adjusted upward by 2 percent per degree of overcooling. For example, a cooling set point of 76°F and a dehumidify set point of 60 percent is equivalent to a cooling set point of 75°F and a dehumidify set point of 62 percent. This dehumidify set point change is internal to the Thermidistat Control and is not shown on the display.

During cool-to-dehumidify demand, the compressor runs a maximum of 10 minutes on, followed by 10 minutes off. When the compressor turns off, the fan (G output) is also turned off immediately. The immediate fan shutoff prevents re-evaporation of water on the coil, improving dehumidifica- tion. If fan is set to continuous, the G (fan on) signal is removed for 5 minutes starting when compressor turns off.

In most furnaces and fan coils, the blower operates for 90 sec after both Y and G disappear. This 90-sec delay should be removed, if possible, for maximum dehumidification perfor- mance. Consult furnace or fan coil Installation Instructions to see if delay can be disabled.

3. Dehumidify Off

Dehumidification can be turned off completely. This can be done without changing existing set points.

To Select Dehumidification (Between NORMAL, COOL TO, and OFF)

Press HUMIDITY button to bring up humidity selections. Succes- sive presses will show "hu" or "dhu" in clock display. Select "dhu" for dehumidify selections. The large display shows actual humidity level. The smaller display (in cool set point location) shows dehumidify set point (DSP) or OF (off). When DSP value is displayed, its value can be changed with up and down buttons. Successive presses of MODE button moves between 3 choices above and each will be indicated as in Table 5.

Superdehumidify (With Cool to Dehumidify)

This selection only affects cool-to-dehumidify operation. It is part of the installer setup (see Configuration Option No. 7) and must be made by installer. The Homeowner's Guide does not cover this selection. A requirement is the use of a variable-speed indoor unit with superdehumidify capability. During cool-to-dehumidify call, it provides maximum dehumidification by reducing airflow to a minimum. The actual superdehumidify command from Thermidis- tat Control to the indoor unit is a Y signal without a G signal in addition to dehumidify signal. The indoor unit responds to this combination by reducing the airflow to a minimum. All other characteristics of cool to dehumidify are the same.

Additional Dehumidify Comments

Dehumidification can be enhanced (with some efficiency loss) by turning blower off immediately at the end of each cooling cycle (eliminating normal 90 sec blower off delay). Where maximum

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