Honeywell CT87B Installation Guide

OFF

ADJUST-
ABLE
HEAT
ANTICIPATOR

COOL

HEAT

HEAT

OFF

COOL

Q539A, CT87A, B INTERNAL SCHEMATIC

TEMP.
FALL

CT87A,B

AUTO

FAN

ON

COOLING
CONTACTOR
COIL

HEATING
RELAY OR
VALVE COIL

COOLING
DAMPER
MOTOR

FIXED 
COOL
ANTICIPATOR

ON

OFF

CO

O

L

HE

AT

FA

N

AU

T

O

M3320

W

1

Y
1

B

O

W

Y

G

R

2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

NO. 4 TERMINAL IS SAME AS B TERMINAL.

1

2

R
1

FAN
RELAY
COIL

R

C

1

HEATING
DAMPER
MOTOR
(IF USED)

FAN
RELAY
COIL

HEATING
RELAY OR
VALVE COIL

HEATING
DAMPER
MOTOR
(IF USED)

COOLING
DAMPER
MOTOR

COOLING
CONTACTOR
COIL

The number will be one of the following: .2, .4, .8 etc., or 0.2, 0.4, 0.8, etc.

If no heat anticipator/indication is showing, do not be concerned; move on to the

next step.

■

■

Loosen screws holding thermostat base to subbase or wall and lift away.

■

■

Disconnect wires from old thermostat or subbase or wallplate. Wrap the wires

around a pencil or other object, as shown, to prevent them from falling back into
the wall opening.

■

■

Push excess wire back into wall.

■

■

Plug hole in wall with nonflammable insulation to prevent drafts from affecting

thermostat operation.

FOR SUBBASE (CT87B heating/cooling systems)

■

■

Refer to illustration above and strip thermostat wire insulation as necessary.

■

■

Connect the wires to matching terminals on the subbase. If your old thermostat

had an R terminal, and your new one has R and RH or RH and RC terminals,
connect the old wire R to terminal RH, and add a jumper to connect RC or R to RH.
The drawing below shows how to jumper RC or R to RH. Strip the insulation off the
wire where it connects to the terminals. Firmly tighten screws.

■

■

Push excess wire back into wall.

■

■

Plug hole with nonflammable insulation to prevent drafts from affecting the

thermostat operation.

CONSUMER PRODUCTS: Honeywell warrants to the consumer that all Honeywell Consumer Products will be
free from defects in workmanship or materials, under normal use and service, for a period one (1) year from date
or original purchase by a consumer. If, at any time during the warranty period, a product is defective or
malfunctions, it should be carefully packaged, along with proof of purchase (including date purchased) and a short
description of the malfunction, and

1) returned to the store from which it was purchased, or
2) mailed, postage prepaid, to the following address:

LIMITED ONE YEAR WARRANTY: This warranty shall not apply if it shown by Honeywell that the defect or
malfunction was caused by damage which occurred while the product was in the possession of a consumer.

Honeywell’s sole responsibility shall be to repair or replace the product within the terms stated above.

HONEYWELL SHALL NOT BE LIABLE FOR ANY CONSEQUENTIAL DAMAGES RESULTING FROM ANY
BREACH OF ANY WARRANTY, EXPRESSED OR IMPLIED, APPLICABLE TO THIS PRODUCT. Some
provinces and territories do not allow the exclusion or limitation of consequential damages, so this limitation may
not 

apply

to you.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, AND THE

WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY
EXCLUDED BEYOND THE ONE YEAR DURATION OF THE WARRANTY. Some provinces and territories do not
allow limitation on the duration of an implied warranty, so the above limitation may not apply to you.

This warranty gives you specific legal rights and you may also have other rights which vary according to

province or territory. This warranty is in addition to and not a modification of or subtraction from warranties and other
rights and remedies contained in Statutes relating to the sale of this product.
Batteries included with Battery Operated Products are excluded from the Warranty as they are not manufactured by
Honeywell Limited. Such batteries are covered by battery manufacturer’s Warranty, if any.

■

■

Turn the transparent dial until the desired point on the setting scale

is in line with the pointer, as shown

.

■

■

To operate the heating

system, set subbase sys-
tem switch at HEAT; to op-
erate cooling, set switch at
COOL. Set at OFF if you
want  neither heating nor
cooling.

■

■

Set fan switch to ON

for continuous fan opera-
tion, or to AUTO for fan
operation during heating or
cooling cycles.

■

■

Align the thermostat over the wallplate or subbase and tighten the

three captive mounting screws (shown in illustration under step 4). These
captive mounting screws complete the electrical connections to the
thermostat.

■

■

Make sure you have the current draw (anticipator setting) for your

system. This is the number you wrote in the box in step 3. If you were
unable to find the current draw for step 3, this information can be found
printed on the primary control at the furnace or boiler. The primary control
is usually a gas valve, a relay or burner control box, Aquastat

controller, or zone valve with the thermostat wires connected to it.
These controls are usually located behind the furnace cover. See illustration

at right.

■

■

Follow the instructions provided by the heating or

heating/cooling equipment manufacturer. If not available, refer to Typical
Wiring Diagrams at the end of this publication.

NOTE:  All wiring must comply with local electrical codes

and ordinances.

■

■

Refer to illustration below and strip thermostat wire insulation as necessary.

NOTE: Clean wire ends thoroughly before connecting.

■

■

Connect either wire to R terminal and the other wire to W terminal. Firmly

tighten screws.

Handle your new thermostat carefully; rough handling can interfere with

its accuracy.

■

■

Remove and discard shipping wrap. Save screws and instructions.

■

■

Remove thermostat cover; set aside until called for later.

Remove material protecting mercury switch bulb.

■

■

Remove cover of old thermostat. If it re-

sists, check for a screw that locks on the cover.

■

■

If installing a CT86A or CT87B, before re-

moving the old thermostat from the wall, look at
it carefully to locate the heat anticipator adjust-
ment mechanism.

(See illustration to help you recognize the heat anticipa-
tor.) Make a note here ______________ of 

that antici-

pator setting for future reference.

Proper installation of your Honeywell thermostat is easy if you follow

these instructions, STEP-BY-STEP. It is recommended that as you read,
understand and complete each step, you check it off.

■

■

Assemble tools required:

Flat blade screwdriver
Wire cutter/stripper or sharp knife
Hand or power drill with 3/16 inch drill bit
Spirit level or plumb bob and line

■

■

Make certain that your burner and/or cooling system are working, especially

if they have been inoperative for any length of time. If either one does not work,
contact your local heating/air conditioning dealer. On cooling systems, do not
operate cooling if outdoor temperature is below 50° F [10° C].

■

■

Turn off power to the system at the main fuse panel. Most buildings have a

separate switch box or circuit breaker for disconnecting power to the furnace.

■

■

Place cover ring on the wall or outlet box at the desired location with

the cable entrance holes to the left. (Use of cover ring is optional for wall
mounting.)

■

■

Bring thermostat cable through the bottom entrance hole of the cover

ring and through the wallplate or subbase entrance hole.

■

■

Fasten the cover ring and wallplate or subbase to the wall or outlet box

with the mounting screws as shown in applicable illustration.

Installation and Owner’s Manual

• CT86A is for 15 to 30 Vac Control of heating-only or

cooling-only systems.

• CT87B is for 15 to 30 Vac control heating/cooling

systems.

• CT86C is for 250, 500 or 750 mV Powerpile heating

systems only.

For heating/cooling system: As you disconnect each
wire, tape the end and label with the letter of the terminal
designation to make reconnection to new subbase or
wallplate easier.
For heating only system: Normally there are only two
wires connected to the old wallplate. They can be con-
nected to the new wallplate W and R terminals. No wire
labelling is necessary.

WIRES THROUGH
WALL OPENING

WIR
WAL

EX
EN
DÈ
PU

1

POWERPILE
PILOT GENERATOR

POWERPILE 
GAS VALVE

PP

PP

TH

TH

HIGH 
LIMIT
CONTROL

CIRCLED WIRING MUST BE APPROVED SAFETY-CIRCUIT 
WIRING

USE R AND W TERMINALS FOR 750 mV SYSTEM. USE R 
AND Y TERMINALS FOR A 250 OR 500 mV SYSTEM.

1

2

M3321

2

CT86C POWERPILE
THERMOSTAT

R

Y

W

■

■

Move the heat anticipator lever to match the

number from step 3 or printed on primary con-
trol, as shown right. If no current draw informa-
tion can be found, leave the anticipator setting
at 4, the factory setting.

■

■

Attach thermostat cover.

FOR STRAIGHT
CONNECTION–
STRIP 5/16 in. [8 mm]

FOR WRAPAROUND
CONNECTION–
STRIP 7/16 in. [11 mm]

M3327

EXAMPLE:  FOR R AND R    OR R    AND R    
JUMPER, STRIP WIRE END LONG ENOUGH
TO JOIN BOTH TERMINALS.

 H 

C

 H 

M6114

WALLPLATE  1

CAPTIVE
MOUNTING
SCREWS (3)

CT86

NO 4 x 1 INCH
SHEET METAL
SCREWS (3)

MOLDED
LEVELING
POSTS

THERMOSTAT
WIRE
ENTERANCE
HOLE

1. USE WALL PLATE FOR HEATING
     ONLY APPLICATIONS (CT86)
2. USE SWITCHING SUBBASE FOR
     HEAT/COOL APPLICATIONS (CT87)

NO 4 x 1 INCH
SHEET METAL
SCREWS (3)

SWITCHING  2
SUBBASE

CAPTIVE
MOUNTING
SCREWS (3)

CT87

THERMOSTAT
WIRE
ENTERANCE
HOLE

1. USE WALLPLATE FOR HEATING ONLY

APPLICATIONS ( CT86)

2. USE SWITCHING SUBBASE FOR

HEAT/COOL APPLICATIONS (CT87)

■

■

Tighten the screws after using spirit level or plumb line to accurately level the

wallplate or subbase. It must be level to maintain accurate calibration.

SPIRIT
LEVEL

LEVELING
POSTS (2)

MOUNTING
SLOTS

M3319A

OPENING FOR
THERMOSTAT
WIRING

M6115

BULB
SWITCH

ANTICIPATOR
SCALE

ANTICIPATOR
SETTING LEVER

The heat anticipator pointer, if adjustable, will be set at one of a series of

numbers representing the current rating of the primary control in your furnace.

■

■

Keep the old thermostat for reference purposes until your new thermostat is

functioning smoothly.

NOTE: Your thermostat should be located about 5 ft. [1.5 m] above the floor in an area

with good air circulation and average temperature. It should not be on an outside
wall.

THERMOMETER

SETTING SCALE

M2685

If this control is replacing a control that contains mercury in a sealed tube,
do not place your old control in the trash. Dispose of properly.
Contact your local waste management authority for instructions regard-
ing recycling and the proper disposal of an old control.

8406 

24 Vac 50/60 Hz

0.4 AMP

30 VAC

0.2 AMP

T

F

T

F

SHOWS
CURRENT 
DRAW

SHOWS 
VOLTAGE
RATING

M6116B

FROM MAIN
FUEL SUPPLY

SHOWS
VOLTAGE
RATING

TO
BURNER

SHOWS
ANTICIPATOR
SETTING

SHOWS
VOLTAGE
RATING

SHOWS
ANTICIPATOR
SETTING

30 VAC

0.2 AMP

T

F

T

F

SHOWS
CURRENT 
DRAW

SHOWS 
VOLTAGE
RATING

M6116B

S

PATOR

NG

LONGER

.15

.12

.2

.6

.8

1.0

.5

.4

.3

HOLE SUITABLE FOR 
PENCIL POINT 
TO MOVE INDICATOR

HEAT 
ANTICIPATOR
INDICATOR

SCALE

Turn down temperature setting to lowest point. If subbase is used, move

system switch to HEAT position. Raise temperature setting until burner
starts. Slowly turn dial back. Burner should stop when dial has been
turned below room temperature. If thermostat controls cooling,

move subbase system switch (if used) to COOL and lower setting until cooling
equipment starts. Raise setting above room temperature and cooling system
should shut down. Make certain equipment functions properly in response to the
thermostat.

Make certain the pilot burner is lit before checking thermostat operation. Then

raise thermostat temperature setting slowly until the burner starts. Note this
setting. Slowly turn dial back. The burner should stop when the dial has been
turned back 1 or 2 degrees below room temperature.