Johnson Controls T25 User manual

Master Catalog 125

Room Thermostats Section T

Product Bulletin T25

Issue Date 1182

Code No. LIT-125640

T25 Type Two-Stage Room Thermostat

Low or Line Voltage--Also for Automatic

Changeover of Heating and Cooling

Application

T25 thermostats are for line or

low voltage service requiring

accurate control of two operating

functions. Choice of functions

include:

•control of two stages of

heating, such as two-rate

unit heaters or duct furnaces,

commercial heat pumps, etc.

•control of two-stages of

cooling, such as two-stage

compressors, dual

compressor units, etc.

•automatic changeover

control of heating and

cooling on three and four

pipe fan coil installations and

similar applications;

automatic changeover from

heating to cooling for unit

operation

All Series T25 thermostats are

designed for use

only

operating controls. Where an

operating control failure

would result in personal injury

and/or loss of property, it is

the responsibility of the

installer to add devices or

systems that protect against,

or warn of, a control failure.

Typical uses are for compressor

control, fan coils, etc. Two

SPDT switches permit

independent control circuits.

Each switch may be wired to

make or break the control circuit

on rise in temperature. A

removable jumper across the

“common” terminals is supplied

as standard.

Features

•Contact units are

dependable, dusttight, field

proven Pennswitches.

•A sensitive liquid charged

element and an efficient

lever mechanism provides

close operating differential

without anticipators.

Fig. 1 -- T25 Two-Stage

Thermostat.

•A bimetal thermometer is

standard.

•A semi-concealed high

temperature stop, which can

be set in the field, is built-in

feature of the thermostat.

•Attractive style matches

other Johnson Controls

thermostats and humidistats.

General Description

T25 thermostats have pleasing,

contemporary styling that is

adaptable to any decor. The

thermometer is a dependable

easy reading, bimetal pointer

type.

The liquid charged sensing

element is formed to achieve

maximum sensitivity to

surrounding air temperature

changes. (See Fig. 2.) Coupled

with a highly efficient diaphragm

and lever mechanism, the

element actuates totally

enclosed Pennswitch contact

units to provide a low operating

differential and dependable

switching action without the

necessity of either heating or

cooling anticipators.

Specifications

2 T25 Product Bulletin

Fig. 2 -- Interior of T25. Note

high temperature stop and

convenient wiring terminals.

Elimination of anticipators

makes every thermostat a

“stock” control, which may be

used on single or two-stage

heating and/or cooling over a

wide range of current loads, at

voltages up to 277 V.A.C.

Thermostats are available with

concealed adjustments. All

thermostats have Allen-head

cover screws to discourage

unauthorized tampering.

T25 thermostats have a

concealed high temperature

stop with adjustments in 2°F

(1.1°C) increments between

68°F (20°C) and 80°F (27°C).

This feature prevents

unauthorized people from setting

the thermostat for temperatures

above a pre-determined

maximum.

Operating Temperature

Differential

The operating temperature

differential of any room

thermostat depends on: the

current flowing through the

thermostat (amperage load); the

velocity of air over the

thermostat; the rate of

temperature change to which the

thermostat is subjected; and,

whether the thermostat is

operating heating or cooling

equipment.

Graphs (Fig. 4, 5) show the

operating temperature

differentials of these thermostats

under various electrical load

conditions.

Fig. 3 -- T25 with concealed

adjustment.

Fig. 4 -- Heating operating

differential for T25.

Fig. 5 -- Cooling operating

differential for T25.

The air velocity was 25 feet per

minute, (.1 m/sec) and the rate

of temperature change was 6°F

(3.3°C) per hour. Higher air

velocities and/or lower rates of

temperature change result in

lower operating differentials.

(See Figs. 4 and 5.)

Optional Constructions

Celsius Dial and Thermometer

Supplied, when specified, at no

extra charge. Thermostat range

of 5 to 30°C. Thermometer

scale 10 to 30°C.

Brand Nameplates

Available on quantity orders.

Check with Customer Service.

Thermostat Guards

Plastic, wire or cast aluminum

guards are available at extra

cost. See GRD Series in the

Johnson Controls Product

Catalog

Ordering Information

To order, specify:

1. T25A for thermostat with

knob adjustment.

2. Specify optional

construction details, as

required:

a. Concealed dial and

adjustment model.

b. Celsius dial and

thermometer.

c. Brand named.

T25 Product Bulletin 3

Repairs and Replacement

Field repairs must not be made

except for replacement of the

knob, faceplate, and cover. For

a replacement thermostat or

parts, contact the nearest

Johnson Controls wholesaler.

4 T25 Product Bulletin

UL Guide No. XAPX

File E6688

Performance specifications appearing herein are nominal and are subject to

accepted manufacturing tolerances and application variables.

Controls Group

507 E. Michigan Street

P.O. Box 423 Printed in U.S.A.

Milwaukee, WI 53201

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