Honeywell T775A Benutzerhandbuch

63-2489—2

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2. For two sensor models (T775B), determine which loads 

will be controlled from sensor A or sensor B and enter on 

the worksheet.

3. Determine setpoint (Setpt) and switching differential 

(Diff) for each load and enter on the worksheet.

4. Refer to the Control Algorithm subsection of Operation 

section to calculate the load on and off temperatures. 

Enter them on the worksheet.

NOTE: Remember that the on/off outputs are off at 

setpoint in both heating and cooling operating 

modes. When in cooling mode, the load turns 

off at setpoint plus the differential. When in 

heating mode, the load turns on at setpoint 

minus the differential.

If this situation results, cooling loads will be energized 

and heating loads will be prevented from energizing. 

The number (1,2,3,4) of these nonenergized loads will 

flash along with the word HEAT to indicate a call for 

both heating and cooling loads controlled by one 

sensor has occurred and to alert the user to reprogram 

the affected control values.

5. Remove the T775 cover and enter the values listed on 

the worksheet and the date in the first column on the 

label inside the T775 cover.

The T775 utilizes a Liquid Crystal Display (LCD) for interactive 

prompting during programming and display of sensed and 

assigned setpoint and differential values. User programming of 

the T775 is accomplished through the four programming keys.

The four programming keys are Select, Up and Down (arrows), 

and Enter:

• Select: Sequentially prompts the user about what parameter 

is being displayed. After the last parameter value is viewed, 

pressing the Select key again displays the control values 

from the beginning of the display loop. The parameters are:

— setpoint, 

— differential, 

— stage energized, 

— heat or cool (operation mode), 

— 1,2,3,4 (indicating assigned stage).

• Up and Down: Allow the displayed parameter to be 

increased or decreased. After pressing Select, a control 

value can be changed using these keys. Control values 

increase or decrease by 1°F or 1°C each time an arrow key 

is pressed.

• Enter: Places the new value in the microprocessor memory.

Press the Select and Enter keys at the same time to change 

the control algorithm from heating to cooling or from cooling to 

heating:

— Heating and cooling parameters are not displayed during 

normal Select key sequences.

— The only parameters displayed after pressing the Select 

and Enter keys at the same time are the stage indication, 

and the word heat or cool.

— To change the operation from heating to cooling (or vice 

versa) for a desired output stage, use the arrow keys.

— The next stage of heat or cool assignment appears after 

pressing the Select key. When all stages are programmed, 

the display reverts to sensed temperature and load 

energized status.

NOTE: Control values and operation selection remain in the 

device memory even after the power is removed.

Once power is applied or restored to the device, the display 

counts down from 210 until the display reads zero. During this 

time all previously energized outputs de-energize. This is 

intended to protect compressors in the event of a power failure.

NOTE: To avoid viewing the entire countdown, press the 

Select key.

The LCD display now shows what it normally reads:

— load (sensed) temperature, 

— stages energized,

— and, for two sensor devices, the sensor (Sensor A or 

Sensor B) being read.

NOTE: At any time during programming, a 60 second pause 

between key presses reverts the display to indicate 

the sensed temperature and stage status.

For two sensor applications, the user has three options for 

display of sensed temperature. The display can be configured 

to:

— lock onto continuous Sensor A,

— lock onto continuous Sensor B sensed temperature,

— alternate between Sensor A and Sensor B (at approximate 

five-second intervals).

Setpt 1

On at

Diff 1

Off at

Setpt 1

On at

Diff 1

Off at

Setpt 1

78°F

On at

Diff 1

4°F

Off at

Setpt 1

78°F

On at

82°F

Diff 1

4°F

Off at

78°F