Honeywell T8424D Installation Instructions Manual Download Page 4

T8424D ELECTRONIC MULTISTAGE THERMOSTAT

69-1386-1

4

Fig. 7. Digital display and system 

switches (FAN and SYSTEM).

Set Temperature Setpoint

NOTE: Temperature setpoint range is 40° to 99°F (5° to 

37°C).

The temperature setpoint and the room temperature are 

shown separately on the digital display. The

 ▼

 indicator 

points to 

Set

 when the temperature setpoint is displayed 

and to 

Room

 when the room temperature is displayed

.

To set temperature setpoint:

1.

Select Heat or Cool by sliding the SYSTEM switch 
in the lower right corner of the thermostat to the 

desired mode. See Fig. 7.

2.

To display the temperature setpoint on the digital 

display, press either the 

 or 

 key once. The 

temperature setpoint is displayed for approxi-

mately five seconds as the indicator points to 

Set

 

and flashes.

3.

To increase the temperature setpoint press the 

 

key. Each press changes the setpoint one degree; 

press and hold to change the setpoint several 
degrees.

4.

To decrease the temperature setpoint press the 

 

key. Each press changes the setpoint one degree; 

press and hold to change the setpoint several 
degrees. 

Setting °F/°C Indication and Heat Cycle Rate

NOTE: To save changes to the °F/°C indication and the 

heat cycle rate, all seven steps must be com-

pleted.

To set the °F/°C indication and heat cycle rate:

1.

If the temperature is displayed in °F, set the tem-

perature setpoint to 52°F. If the room temperature 
is displayed in °C, set the temperature setpoint to 

11°C. 

2.

Press the 

▲▼

 keys simultaneously for more than 

one second to light all segments on display and to 

enter installer setup mode. When the keys are 
released, a two-digit software revision code is dis-

played.

OPTIONAL SYSTEM CHECKOUT 

When in steps 2 and 3 only, the 

 key can be used to 

turn heat or cool outputs on and off. Change the 
SYSTEM switch setting to test heat or cool outputs. No 

action takes place If the system switch is in the Off 
position.

Examples: System setting at HEAT: If heat is on, the 

 

key turns it off; if heat is off, 

 turns it on.

System setting at COOL: If cool is on, 

 key 

turns it off; if cool is off, 

 turns it on.

NOTE: In Optional System Checkout for multistage 

models, pressing the 

 key turns on the first 

stage output. (The second press of the 

 key 

turns on the second stage output.)

NOTE: In installer setup mode only, each press of the 

 key momentarily displays 01. Each press of 

the 

 key momentarily displays 02. When the 

keys are released, these two-digit codes are no 

longer displayed. 

SYSTEM

Cool  O

ff  H

eat

Auto  On

FAN

M14678

TEMPERATURE DISPLAY

INCREASE SETTING

DECREASE SETTING

FAN SWITCH

SYSTEM SWITCH

Set

Room  

INDICATOR

ROOM TEMPERATURE

SETPOINT TEMPERATURE

M14679

M14680

M14681

M14682

M14683

M14686

M14684

M14685

Summary of Contents for T8424D

Page 1: ...le for your application 3 Installer must be a trained experienced service technician 4 After installation is complete check out product operation as provided in these instructions CAUTION Electrical Shock or Equipment Damage Hazard Can shock individuals or short equipment circuitry Disconnect power supply before installation Location Install the thermostat about 5 ft 1 5m above the floor in an are...

Page 2: ... shape of the terminals permits insertion of straight or wraparound wiring connections either method is acceptable See Fig 4 The T8424 Thermostat is powered through the system transformer and is adaptable to most 24 Vac multistage heating cooling systems Refer to Fig 5 for typical wiring hookups Fig 3 Restrict wiring to shaded area 5 FEET 1 5 METERS YES NO NO NO M11338 M12202A WALL WALL ANCHORS 2 ...

Page 3: ...e heating equipment turns on on most systems When using an electric heat thermostat the fan starts and stops with the heating equipment Slide the FAN switch in the bottom left corner of the thermostat to select the desired fan setting SYSTEM Switch System switch settings control thermostat operation as follows Cool The thermostat controls the cooling system Off Both heating and cooling are off Hea...

Page 4: ... set the F C indication and heat cycle rate 1 If the temperature is displayed in F set the tem perature setpoint to 52 F If the room temperature is displayed in C set the temperature setpoint to 11 C 2 Press the keys simultaneously for more than one second to light all segments on display and to enter installer setup mode When the keys are released a two digit software revision code is dis played ...

Page 5: ...thm C3 Aggressive algorithm can cause overshooting 13 Press the key again Current configuration CC is displayed A typical example is shown but CC varies by model This information is for factory use only Table 1 Heating Cycle Rates for Stage Two Heating a High efficiency furnace bRefer to equipment manufacturer s instructions 14 Press the key to save all changes exit installer setup mode and return...

Page 6: ... Press the key to lower the temperature setting several degrees below the room temperature After approximately five minutes the cooling equipment should start The fan starts and stops with the cool ing equipment 3 Press the key to raise the temperature setting above the room temperature Cooling system should shut down NOTE To bypass the 5 minute delay see the Optional System Checkout section Fan 1...

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