Bryant Q674 Manual

A SERVICE OF

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—812

anticipator at 140 percent of the actual primar

y

con-

trol current draw to reduce the c

y

clin

g

rate. See Fi

g

.

11.

Most heat pump s

y

stems should c

y

cle 2-1/2 to 3 times per hour.

4.

Han

g

the upper ed

g

e of the thermostat cover on top of

the thermostat base and swin

g

the cover downward

until it en

g

a

g

es with the cover clip.

Fig. 11. Adjustable heat anticipator scales.

Temperature Setting

Move the heatin

g

and coolin

g

levers to the desired comfort

positions. See Fi

g

. 12. On some models with two sta

g

es of

heatin

g

or coolin

g

, the same lever controls both sta

g

es. The

minimum differential between heatin

g

and coolin

g

setpoints is

4°F

(

2°C

)

(

5°F [3°C]

)

on T874W.

If model has optional screws to lock temperature control

levers, loosen these screws before makin

g

temperature

ad

j

ustment; ti

g

hten the screws when levers are set at desired

position.

Fig. 12. Internal view of T874W (three stages of

heating, two stages of cooling).

Subbase Setting

The subbase switchin

g

positions control the s

y

stem operation

as described below.

SYSTEM SWITCH

(

see subbase for positions

)

:

OFF—both the heatin

g

and coolin

g

s

y

stems are off. If the

fan switch is at the AUTO position, the coolin

g

fan is

also off.

HEAT—heatin

g

s

y

stem is automaticall

y

controlled b

y

the

thermostat. Coolin

g

s

y

stem is off.

AUTO—thermostat automaticall

y

chan

g

es between heat-

in

g

and coolin

g

s

y

stem operation, dependin

g

on the

indoor temperature.

COOL—coolin

g

s

y

stem is automaticall

y

controlled b

y

the

thermostat. Heatin

g

s

y

stem is off.

EM.HT.—emer

g

enc

y

heat rela

y

is automaticall

y

controlled

b

y

the thermostat. Coolin

g

s

y

stem is off. Compressor is

de-ener

g

ized.

SUPL.HT.—supplemental heat rela

y

is ener

g

ized. Coolin

g

s

y

stem is off. Compressor is de-ener

g

ized.

WOOD—heatin

g

s

y

stem is operatin

g

with onl

y

the wood-

burnin

g

sta

g

e.

OIL—heatin

g

s

y

stem is operatin

g

with onl

y

the oil-burnin

g

sta

g

e.

WOOD/OIL—wood and oil sta

g

es operate se

q

uentiall

y

;

first the WOOD sta

g

e operates, then the OIL sta

g

e

operates if the WOOD sta

g

e cannot handle the load.

EVAP—controls coolin

g

s

y

stem b

y

water evaporation; see

e

q

uipment instructions for further information.

OVERRIDE—ni

g

ht setback is disabled.

ON—heatin

g

s

y

stem is controlled b

y

the thermostat. EM.

HT. or SUPL. HT. rela

y

is not ener

g

ized.

FAN SWITCH

positions control fan operation as follows:

ON or CONT.—fan operates continuousl

y

.

AUTO—fan operates as controlled b

y

the thermostat in

heat pump s

y

stems or conventional coolin

g

mode; fan

operates as controlled b

y

the plenum switch in conven-

tional heatin

g

mode.

LO—fan operates constantl

y

at low speed.

MED—fan operates constantl

y

at medium speed.

HI—fan operates constantl

y

at hi

g

h speed.

To move the subbase switches to the desired control

positions, use thumb and index fin

g

er to slide the lever. The

lever must stop over desired function indicator position for

proper circuit operation.

Sprin

g

return momentar

y

position switchin

g

feature is

available on selected subbase models. On these models, the

fan switch is positioned to the ri

g

ht of the s

y

stem switch. B

y

movin

g

the fan switch to the far ri

g

ht and releasin

g

it, the ON

position circuit makes. The lever sprin

g

s back on release. This

position is not marked on the subbase.

Setting the Adjustable Differential

The ad

j

ustable intersta

g

e differential feature, on a selected

T874D model onl

y

, can be identified b

y

the scale and tension

screw near the heatin

g

and coolin

g

mercur

y

switches. See

Fi

g

. 13. On this model, the number of de

g

rees between the

makin

g

of the first and second sta

g

e mercur

y

bulbs is

ad

j

ustable. This feature is especiall

y

useful if the first sta

g

e

controls the comfort temperature, and the second sta

g

e

controls the ener

gy

savin

g

s temperature. Timers, such as the

S6005, for insertion between the first and second sta

g

e

control points must be ordered separatel

y

.

1.2

.4

.6

.3

.2

.15

.12

.1

0

.8

1.2

.4

.6

.3

.2

.15

.12

.8

.5

MOVE INDICATOR TO

MATCH CURRENT RATING

OF PRIMARY CONTROL

STAGE ONE

ANTICIPATOR

HEATING

CONTROL

STAGE TWO

ANTICIPATOR

HEATING CONTROL

M5069

STAGE 1

HEATING

STAGE 3

HEATING

STAGE 2

HEATING

HEATING

LEVER

COOLING

LEVER

STAGE 1

COOLING

STAGE 2

COOLING

CAPTIVE

MOUNTING

SCREWS (2)

M7625