To prevent electrical shock and/or equipment damage,
disconnect electric power to system at main fuse or
circuit breaker box until installation is complete.
Base
Back of
Thermostat Body
RC
G
RH
Y
O
B
W
W904
W905
Mounting
Hole
Mounting
Hole
Figure 1. Thermostat
W904 - clip for Celcius display
W905 - clip for hydronic system
NOTE:
Earlier models refer to 37-7006 for jumper locations.
Heating & Air Conditioning
1E78
Non-Programmable Heat Only Thermostat
PART NO. 37-6620B
Replaces 37-6620A
1026
Installation Instructions for
YOUR THERMOSTAT REPLACES
Typical System Compatibility Chart
1E78
Standard Heat Only Two Wire Gas or Oil Fired Systems (24 volt)
Yes
Electronic Ignition Heat Only Two Wire Systems (24 volt)
Yes
Electronic Ignition Heat Only Gas or Oil Fired Systems (24 volt)
Yes
Standard Heat/Cool Systems (24 volt)
No
Heat/Cool Systems Electric Heat (24 volt)
No
Heat Only Electric Heat Systems (24 volt)
No
Cool Only Systems
No
Heat Pump Systems (No Aux. or Emergency Heat)
No
Hot Water Zone Heat Only (Two Wire) Systems
Yes
Hot Water Zone Heat Only (Three Wire) Systems
No
Line Voltage Heating or Baseboard 110/240 Volt Systems
No
Millivolt Systems Floor or Wall Furnaces
Yes
12 VDC Mobile Home Application
Yes
Multistage Systems
No
Systems Exceeding 30VAC, 1.5 Amp
No
Assemble tools required as shown below.
HAND OR POWER
DRILL WITH 3/16 INCH
DRILL BIT, IF NEEDED
FLAT BLADE SCREWDRIVER
WIRE CUTTER/STRIPPER
3
REMOVING OLD THERMOSTAT
1
PREPARATIONS
2
THERMOSTAT DETAILS
Before removing wires from old thermostat’s switching subbase,
label each wire
with the terminal designation it was removed
from.
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
the mounting screws that hold it on the wall or adaptor
plate.
2.
Shut off electricity at the main fuse box until installation is
complete. Ensure that electrical power is disconnected.
3.
Remove the front cover of the old thermostat.
With wires
still attached,
remove wall plate from the wall. If the old
thermostat has a wall mounting plate, remove the thermostat
and the wall mounting plate as an assembly.
4.
Identify each wire attached to the old thermostat using
the labels enclosed with the new thermostat.
5. Disconnect the wires from the old thermostat one at a time.
DO NOT LET WIRES FALL BACK INTO THE WALL.
6. Install new thermostat using the following procedures.
CONTENTS
Preparations ................................................ 1
Thermostat Details ...................................... 1
Removing Old Thermostat ........................... 1
Mounting and Wiring .................................... 2
Check Thermostat Operation ....................... 3
Specifications .............................................. 4
Troubleshooting ........................................... 4
Failure to follow and read all instructions carefully
before installing or operating this control could cause
personal injury and/or property damage.
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CAUTION
!