Honeywell Q674A-E, Q674A-G, T874A-F installation instructions

160-1165—6

Q674 Switch Positions

Model System Fan

A Heat-Auto-Cool Auto-On

B Heat-Off-Cool Auto-On

C Off-Auto Auto-On

D None None

E Off-Heat-Auto-Cool Auto-On

G Off-Auto None

T874A-F MultistageThermostats/Q674A-E,G Subbases

TRADELINE®

Installation Instructions for the Trained Service Technician.

Operation

On a 2-heat thermostat, the two stages of heat make

sequentially as the temperature drops. Make refers to the

mercury switch initiating a call for heat or cool.

There are about 2° F [1° C] between stages so that the

second stage makes only when the first stage cannot handle

the load. This is the interstage differential.

M3375

Recycling Notice

This control contains mercury in a sealed tube. Do not

place control in the trash at the end of its useful life.

If this control is replacing a control that contains mer-

cury 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

this control, or of an old control containing mercury in a

sealed tube.

Installation

WHEN INSTALLING THIS PRODUCT…

1. Read these instructions carefully. Failure to follow

them could damage the product or cause a hazardous condi-

tion.

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 tech-

nician.

4. After installation is complete, check out product

operation as provided in these instructions.

CAUTION

1. Disconnect power supply to prevent electrical

shock or equipment damage.

2. To prevent interference with the thermostat

linkage, keep wire length to a minimum and

run wires close as possible to the subbase.

3. Do not overtighten thermostat captive mount-

ing screws because damage to subbase threads

can result.

4. Do not short across coil terminals on heating

relay or gas control. This can burn out the

thermostat heat anticipator.

IMPORTANT: Thermostats are calibrated at the factory

by using subbases mounted at true level. Inaccurate

subbase leveling will cause thermostat control de-

viation.

LOCATION

Locate the subbase about 5 ft [1.5m] above the floor in

an area with good air circulation at average temperature.

Do not mount the subbase where the thermostat may be

affected by:

—drafts or dead spots behind doors and in corners.

—hot or cold air from ducts.

—radiant heat from sun, appliances or fireplace.

—concealed pipes and chimneys.

—unheated (uncooled) areas such as an outside wall

behind the thermostat.

MOUNTING THE SUBBASE

The thermostat subbase can be mounted on a vertical

outlet box, horizontal outlet box or directly on the wall.

1. If you must mount the subbase on a vertical outlet

box, order Honeywell 193121A Adapter Assembly (Fig. 1).

The assembly includes an adapter ring, two screws and a

cover plate to cover marks on the wall. Install the ring and

cover plate on the vertical outlet box.

Application

The T874A-F Thermostats provide 24 to 30 Vac control

for heating and/or cooling systems as listed in Table 1.

TABLE 1—THERMOSTAT HEATING AND/OR

COOLING STAGES.

The Q674A-E,G Subbases provide wiring terminals,

system and fan switching, and mounting bases for T874

Thermostats as listed in Table 2.

TABLE 2—SUBBASE SWITCHING POSITIONS.

T874 A B C D E F

Heating Stages 1 122—2

Cooling Stages 1 2122—

M3375