Honeywell t8424d Installation Instructions Manual

Multistage Thermostat

The T8424 Thermostat provides electronic control of
single-zone, multistage heating and cooling systems.
First and second stage cooling cycle rates are fixed at 3
cph. Heating cycle rate is selectable. Temperature
indication can be set for °F or °C.

The T8424 Thermostat is powered from the system
transformer. Batteries are not required because setpoints
are held permanently by non-volatile memory.

The T8424 includes a thermostat, wallplate (for wiring
and mounting thermostat) and owner ’s guide.

MERCURY NOTICE

If this control is replacing a control that contains
mercury in a sealed tube, do not place your old
control in the trash.

Contact your local waste management authority
for instructions regarding recycling and the
proper disposal of an old control containing
mercury in a sealed tube.

If you have questions, call Honeywell Inc. at
1-800-468-1502.

INSTALLATION

When Installing this Product…

1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard­ous condition.

2. Check the ratings given in the instructions and on
the product to make sure the product is suitable 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.

T8424D Electronic

INSTALLATION 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 area with good air circulation at average temperature.
See Fig. 1. Do not install the thermostat where it can be
affected by:
— drafts or dead spots behind doors and in corners.
— hot or cold air from ducts.
— radiant heat from the sun or appliances.
— concealed pipes and chimneys.
— unheated (uncooled) areas such as an outside wall

behind the thermostat.

This thermostat is a precision instrument and was
carefully adjusted at the factory. Handle it carefully.

Mounting Wallplate to Wall

IMPORTANT

Level only for appearance. The thermostat func­tions normally even when not level.

Mount wallplate, T8424 and the screws provided (see
Fig. 2) as follows:

1. Place the wallplate at the desired location on the
wall.

2. Pull the thermostat wire through the entrance hole
on the decorator cover plate, then through the wall­plate entrance hole.

3. Select the two mounting holes that best fit the
application.

4. Fasten the wallplate to the wall using the anchors
and screws provided.

5. After wiring the wallplate, plug the hole to prevent
drafts from affecting the thermostat; see Wiring
section.

® U.S. Registered Trademark
Copyright © 2001 Honeywell • • All Rights Reserved

69- 1386- 1

T8424D ELECTRONIC MULTISTAGE THERMOSTAT

Wiring

NO

WALL

MOUNTING
SCREWS (2)

1

WHEN USING WALL ANCHORS, DRILL 3/16 INCH
HOLES FOR DRYWALL, 7/32 INCH HOLES FOR
PLASTER OR WOOD.

WALL
ANCHORS (2)

1

WALLPLATE

Fig. 2. Mounting wallplate to wall.

YES

NO

5 FEET

[1.5 METERS]

Fig. 1. Typical location of thermostat.

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.

KEEP WIRING IN
SHADED AREA

G

C

W1

M12202A

NO

M11338

R

W2

Y2

B

Y

O

IMPORTANT

Use an 18-gauge maximum wire for wiring the
T8424 Thermostat.

All wiring must comply with local electrical codes and
ordinances. Disconnect the power supply to prevent
electrical shock or equipment damage.

NOTE: To ensure proper mounting of thermostat,

restrict all wiring to the shaded area. See Fig. 3.

The shape of the terminals permits insertion of straight or
wraparound wiring connections; either method is
acceptable. See Fig. 4.

69-1386-1 2

MOUNTING
SCREW HOLE

WIRING ENTRANCE
HOLE

Fig. 3. Restrict wiring to shaded area.

MOUNTING
SCREW HOLE

M20211