CONTENTS
Preparations ...........................................
Thermostat Features ..............................
Removing Old Thermostat .....................
Mounting and Wiring ..............................
Set Heat Anticipator ...............................
New Thermostat Operation ....................
Specifications .........................................
1
2
3
4
5
6
7
Installation Instructions for
Heating only
1C20
and
Heating & Cooling
Troubleshooting ..................................... 8
8
1C26
PREPARATIONS
YOUR THERMOSTAT REPLACES
1
Assemble tools required as shown below.
Description
1C20
No
1C26
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Standard Heating & Cooling Systems - 4 or 5 wires
Standard Heat Only Systems
Yes
Yes
No
Millivolt Heat Only Systems - Floor or Wall Furnaces
Standard Central Air Conditioning
Gas or Oil Heat
FLAT BLADE SCREWDRIVER
WIRE CUTTER/STRIPPER
Yes
Yes
Yes
No
HAND OR POWER
DRILL WITH 3/16 INCH
DRILL BIT, IF NEEDED
Electric Furnace
Hydronic (Hot Water) Zone Heat - 2 Wires
Hydronic (Hot Water) Zone Heat - 3 Wires
Heat Pump (No Aux or Emergency Heat)
Heat Pump (with Aux or Emergency Heat)
Baseboard Electric Heating or Line Voltage (120 or 240 Volt)
SPIRIT LEVEL OR PLUMB BOB AND LINE OPTIONAL—
THERMOSTAT MUST BE LEVEL TO WORK PROPERLY
No
Yes
No
No
Failure to follow and read all instructions carefully be-
fore installing or operating this control could cause
personal injury and/or property damage
No
No
THERMOSTAT FEATURES
REMOVING OLDTHERMOSTAT
2
3
CAUTION
!
MOUNTING SCREWS
To prevent electrical shock and/or equipment damage,
disconnect electrical power to the system at the main
fuse or circuit breaker until installation is complete.
ANTICIPATOR
Before removing wires from old thermostat’s switching subbase,
label each wire with the terminal designation it was removed from.
Some models also include an adaptor plate to cover unpainted
surfaces. Thermostat wires pass through the adaptor plate center
opening.
CAPTIVE SCREWS
SUBBASE
(MODEL 1C26
ONLY)
1. Remove Old Thermostat: A standard heat/cool thermostat
consists of three basic parts:
a. The cover, which may be either a snap-on or hinge type.
b. The base, which is removed by loosening all captive screws.
c. The switching subbase, which is removed by unscrewing
themountingscrewsthatholditonthewalloradaptorplate.
BASE
Make a note here
of the anticipator setting on
the old thermostat for future reference and use in step 5.
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. The number will be one of the following:
.2, .4, .8, etc. or 0.2, 0.4, 0.8, etc.
COVER
Adaptor Plate
(optional)
If no heat anticipator/indication is showing, do not be concerned;
move on to the next step.
Figure 1.
PART NO. 37-6335B
Replaces 37-6335A
0835
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SET HEAT ANTICIPATOR
5
Set anticipator to match the setting of your old thermostat you
noted in Step 3, or, the anticipator should be set to match the
current rating stamped on your main heating control. The heat
anticipator is adjustable from 0.15 to 1.2 amps. Adjust the antici-
pator by rotating the contact arm (see fig. 5). The anticipator
setting is indicated by the numbers on the base that the pointer
points to. If you are unsure where to set the anticipator contact the
heater manufacturer for a recommended setting.
Rotate contact arm
to adjust heat anticipator
NOTE
For Milivolt Application:
Rotate contact arm
to rest on this rivet.
Movethepointer counterclockwise to lengthen heatingsystem
cycles; move clockwise to shorten heating cycles. Adjustments
should not be greater than 1/2 marking at a time.
Arrow points to the
current rating of
the primary coontrol
Snap on Cover: Carefully align the cover with the base and snap
the cover onto the base.
Figure 5. Anticipator adjustment
Typical Zone Valve
Typical Gas Valve
Typical Oil Primary
24VAC
50/60 Hz
.43 Amps
24VAC
24VAC
50/60 Hz
.35 Amps
50/60 Hz
.23 Amps
NEW THERMOSTAT OPERATION
1C20 Heat Only – After power is turned on, slide temperature
lever to desired setting. To turn heat off, slide lever all the way to
the left until it clicks.
Shows switch position
6
FAN
SYSTEM
OPERATION
AUTO ON
COOL OFF HEAT
No heating; no cooling; no fan
1C26 – This thermostat is easy to operate. Fig. 6 shows how the
heating/cooling system and fan operate when the switches are in
various positions. After power is turned on, use the system switch
to select either heating or cooling, or to turn the heating/cooling
system off. Use the fan switch to control fan operation. When the
fan switch is in the AUTO position, the fan will cycle with the
heating or cooling system (the fan will not run if the system switch
is in the OFF position and the fan switch is in the AUTO position).
When the fan switch is in the ON position, the fan will run
continuously, regardless of system switch position (even if the
system switch is set to OFF, the fan will run if the fan switch is in
the ON position).
No heating; no cooling; fan runs continuously
Cooling system cycles from thermostat; fan runs
continuously
Cooling system and fan cycle from thermostat
Heating system cycles from thermostat; fan cycles
from fan control on furnace
Heating system cycles from thermostat; fan runs
continuously
Figure 6. Subbase switching and thermostat/system
operation (1C26 only)
SPECIFICATIONS
ELECTRICAL DATA
7
THERMAL DATA:
Temperature Range ..............50°F to 90°F (10°C to 32°C)
Operating Humidity Range ... 0 – 90% noncondensing
Switch Rating ........................ 24 VAC (30 VAC max.)
Heating.................................... 0.15 to 1.2 Amps
Cooling .................................... 0 to 1.5 Amps
Switch Action ........................ Snap Action
Anticipator Rating:
Heating.................................... Adjustable from 0.15 to 1.2 Amps
Cooling .................................... Fixed
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TROUBLESHOOTING
8
Symptom
Possible Cause
Corrective Action
No Heat/No Cool/No Fan
(common problems)
1. Blown fuse or tripped circuit breaker.
2. Furnace power switch to OFF.
Replace fuse or reset breaker.
Turn switch to ON.
3. Furnace blower compartment door or
panel loose or not properly installed.
Replace door panel in proper position to engage
safety interlock or door switch.
No Heat
1. Pilot light not lit.
Re-light pilot.
2. Broken or melted anticipator wire.
Excessive current or dead short in system. Have
a qualified service person check the system
before replacing thermostat.
3. Loose connection to thermostat or system.
Verify thermostat and system wires are securely
attached.
4. Thermostat or heating system requires
replacement or service.
Your furnace manufacturer or service person can
describe how to test the heating system to verify
it is operating correctly. If the heating system is
capable of operation and the no heat condition
persists, replace the thermostat.
5. System Switch not set to Heat.
1. Furnace Lock-Out Condition
Set System Switch to Heat and raise temp above
room temp.
Intermittent Heat
No Cool
Many furnaces have safety devices that shut the
system down when a lock-out condition occurs. If
the heat works intermittently contact the furnace
manufacturer or local service person for assistance.
1. Loose connection to thermostat or system.
Verify thermostat and system wires are securely
attached.
2. Thermostat or cooling system requires
replacement or service.
Your cooling system manufacturer or service
person can describe how to test the cooling
system to verify it is operating correctly. If the
cooling system is capable of operation and the no
cooling condition persists, replace the thermostat.
3. System Switch not set to Cool.
Set System Switch to Cool and lower temp below
room temp.
Heat, Cool or Fan Runs Constantly.
1. Possible short in wiring.
2. Possible short in thermostat.
3. Possible short in heat/cool/fan system.
Check each wire connection to the thermostat to
verify it is neatly looped under the terminals. No
extra wire should stick out from under the
terminals.
Furnace Cycles Too Fast or Too Slow
Narrow or wide temperature swing
See Step 5, Adjusting the Anticipator.
The anticipation setting is the only adjustment that
effects the heating cycle rate. If an acceptable
cycle rate is not achieved using the anticipator
contact a local service person for additional
suggestions. The location of the thermostat, size
of the Heat/Cool System and current draw can
influence the cycle rate.
Cooling Cycles Too Fast orToo Slow
(narrow or wide temperature swing)
1. Poor thermostat location for sensing room
temperature.
2. Cooling system over or undersized.
3. Excessive Current draw influencing thermostat.
The cycle rate for cooling can not be adjusted.
The location of the thermostat, size of the Cool
system and current draw can influence the cycle
rate. Contact a local service person for suggestions.
Thermostat Setting and Thermostat
Thermometer Disagree
1. Thermostat thermometer setting requires
adjustment.
The thermometer can be adjusted by using a
standard slotted screwdriver. Turn the thermom-
2. Thermostat setting lever requires calibration. eter pointer screw located inside the front cover
to change the setting. For calibrating the setting
lever contact a local heating and cooling service
person.
Adjusting Thermometer
1. Thermostat thermometer disagrees with
other room thermometers.
The thermometer on the thermostat is accurately
calibrated at our factory but you can adjusted it
by using a standard slotted screwdriver. Turn the
thermometer pointer screw located inside the
front cover to change the setting.
The Emerson logo is a
trademark and a service mark
of Emerson Electric Co.
White-Rodgers is a division
of Emerson Electric Co.
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