DIGITAL
NON-PROGRAMMABLE
THERMOSTAT
8
425
ELECTRIC
E
GAS
G
OIL
O
®
NeW
2 Heat / 2 Cool
User's Manual
Quick Start
Installation
HEAT PUMP
H
110-1090B
Application
The Robertshaw 8425 is a multi-stage thermostat designed to control
24 VAC heat pump systems.
Features
• Large backlit display
• Adjustable 1
1.5°C)
• Adjustable 2
3.0°C)
• Adjustable 2
• Compressor short cycle protection
• Accuracy within ±1°
• Zone system compatible as a master thermostat
• Permanent memory retention
• Fahrenheit/Celsius display option
• Adjustable from 45°F to 90°F (7°C - 32°C)
• Quick wire terminal block
st
stage temperature differential: 1.0°F to 3.0°F (0.5°C to
nd
stage temperature differential: 1.0°F to 6.0°F (0.5°C to
nd
stage delay (10-40 minutes)
1
!
WARNING:
• Always turn off power at main fuse or circuit breaker panel before
installing, removing, cleaning, or servicing thermostat.
• Read all the information in this manual before installing this thermostat.
• DO NOT CONNECT TO 120 VAC. This is a 24 VAC low-voltage
thermostat. Do not install on voltages higher than 30 VAC.
• All wiring must conform to local and national building and electrical
codes and ordinances.
• Do not short (jumper) across terminals on the gas valve or at the
system control to test installation. This will damage the thermostat
and void the warranty.
• Do not connect ground to any terminal in this unit.
Recycling Thermostat
If this thermostat REPLACES a thermostat that contains mercury,
DO NOT discard the old thermostat in the regular trash. Mercury
is harmful to humans and the environment. For this reason, do
not open, break, or crush the mercury cell. If mercury leaks from
a damaged cell, DO NOT touch or handle mercury with bare
hands. Use protective, non-absorbent gloves to place mercury
into a sealable container. Fill the container with sand or another
absorbent material and seal the container completely.
Return the mercury or mercury products, in a sealed container, to
Invensys Controls Americas or a local recycling center for proper
disposal. If you have any questions, call Robertshaw technical
support at 1-800-445-8299.
Invensys Controls Americas
28C Leigh Fisher Blvd.
El Paso, TX 79906
Attn: Mercury Recycling Center
Step 1: Replacing Existing Thermostat
Wiring Table
Old Terminal New Label Description
R, V-VR or VR-R R 24VAC, return
Y, Y1, M Y1 Compressor relay (Stage 1)
O or R O Reversing valve (cool active)
B B Reversing valve (heat active)
F or G G Fan control relay
Y2 Y2 2ndstage cooling circuit
W2, W-U or E W2/E 2ndstage heating control or
emergency heating for heat pumps
C, X or B C 24 VAC, transformer common side
L or X L System monitor
W or W1 W1 1st stage heat - non heat pump
NOTE: THIS THERMOSTAT REQUIRES A 24 VAC COMMON WIRE FOR PROPER OPERATION.
NOTE: ON SOME OLDER MODELS, THE C TERMINAL CAN BE EITHER THE COOLING CONTROL OR
THE COMMON SIDE OF THE TRANSFORMER. CHECK FURNACE WIRING DIAGRAM TO VERIFY C
TERMINAL. IF IT IS THE COMMON SIDE OF THE TRANSFORMER, CONNECT TO THE C TERMINAL.
2
emer heat off cool
auto on
°
F
!
WARNING:
In heat pump applications, do not connect anything to the W1
terminal. When switched to HP mode, W1 is connected internally
to Y1 on the thermostat.
1. Turn off power to heating and cooling system.
2. Remove cover from old thermostat to expose wires (Figure 1).
3. Disconnect wires one at a time from existing terminals. Use enclosed
labels to mark existing wires. Refer to cross references in the Wiring Table
if existing wiring does not directly match the labels.
4. Remove existing thermostat base from wall.
Figure 1
Step 2: Installing Model 8425 Thermostat
NOTE: FOR NEW INSTALLATIONS, MOUNT THERMOSTAT ON
INSIDE WALL, FIVE FEET ABOVE THE FLOOR. DO NOT
INSTALL BEHIND A DOOR, IN A CORNER, NEAR AIR
VENTS, IN DIRECT SUNLIGHT, OR NEAR ANY HEAT OR
STEAM GENERATING FIXTURES. INSTALLATION AT THESE
LOCATIONS WILL AFFECT THERMOSTAT OPERATION.
1. Turn power off to the heating and cooling systems.
2. Place EMER-HEAT-OFF-COOL in OFF position (Figure 2).
3. Place AUTO-ON switch into AUTO position (Figure 2).
emer heat off cool
auto on
°
F
Figure 2
3
4. Remove the cover using a coin or screwdriver (Figure 3). Set aside.
auto on
at off cool
he
°
F
N
O
M
set
vac
p
clock
tem
hold
hold
run/set
prog
Figure 3
5. Place thermostat against the wall at desired location. Make sure
wires will feed through opening (Figure 4) on base of thermostat.
Mounting Holes
°
F
GOB Y1W1
C
R
L
ELEC GAS
NON_HP HP
Y2
W2/E
Figure 4
6. Mark placement of mounting holes (Figure 4). Set base aside.
7. If mounting on drywall, tap plastic anchors into wall.
NOTE: Enclosed plastic anchors do not require a drilled hole
for drywall.
8. If mounting on a surface other than drywall, drill the marked holes
using a 3/16" (5mm) drill bit.
9. Align base with plastic anchors and feed wires through opening.
10. Secure base to wall with supplied screws. NOTE: The thermostat
will mount horizontally on a single gang junction box.
11. Strip end of wires 5/16” (8mm) if needed.
12. Terminal screws are already loose and ready for wire insertion.
Insert wires into terminal strip (Figure 4) matching the label to the
corresponding terminal (see Wiring Diagrams). Tighten screws.
13. Make sure wire connections are secure.
14. Push excess wire back through opening.
4
Hot
Heating
Control
Cooling
Control
Transformer
T
H
E
R
M
O
S
T
A
T
W1
C
R
Y1
G
O
B
24 VAC
120 VAC
HEAT/COOL
4-WIRE
SINGLE TRANSFORMER
Fan
Control
Y2
W2/E
Hot
Heating
Control
Transformer
24 VAC
120 VAC
HEAT ONLY
2-WIRE
SINGLE TRANSFORMER
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
HEAT/COOL
2 STAGE
Hot
Transformer
24 VAC
120 VAC
T
H
E
R
M
O
S
T
A
T
R
C
L
W1
Y1
B
O
G
Y2
W2/E
First Stage
Cool
First Stage
Heat
Second
Stage Heat
Second
Stage Cool
Fan
Control
Hot
Cooling
Control
Fan
Control
Transformer
24 VAC
120 VAC
COOL ONLY
3-WIRE
SINGLE TRANSFORMER
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
Hot
Heating
Control
Fan
Control
Transformer
24 VAC
120 VAC
HEAT ONLY
SINGLE TRANSFORMER
3-WIRE
W1
Y1
G
T
H
E
R
M
O
S
T
A
T
O
B
C
R
Y2
W2/E
♦ Wiring Diagrams
5
HEAT PUMP WITH
,
COOL ACTIVE
REVERSING VALVE
HEAT PUMP WITH
HEAT ACTIVE
REVERSING VALVE
Contactor
Fan
Relay
Reversing
Valve
R
C
W1
Y1
G
O
B
Y2
W2/E
Transformer
Hot
120 VAC
24 VAC
Compressor
NOTE: Make sure the HP swtich is in the HP
position. When switched to HP mode,
W1 is connected internally to Y1.
HEAT PUMP + AUX COOL
COOL ACTIVE
REVERSING VALVE
Valve
Fan
Control
Second
Heat
R
C
L
W1
Y1
B
O
G
Y2
W2/E
Transformer
120 VAC
Hot
Compressor
Fault Output
(24VAC)
24 VAC
Compressor
Contactor
Reversing
Stage Cool
Aux/Emer
Contactor
Fan
Relay
Reversing
Valv e
Y2
W2/E
R
T
C
H
E
W1
R
M
Y1
O
G
S
T
O
A
B
T
T
H
E
R
M
120 VAC
Transformer
Hot
24 VAC
Compressor
O
S
T
A
T
NOTE: Make sure the HP swtich is in the HP
position. When switched to HP mode,
W1 is connected internally to Y1.
HEAT PUMP + AUX HEAT
HEAT ACTIVE
REVERSING VALVE
Valv e
Heat
R
T
H
C
E
L
R
M
W1
O
S
Y1
T
B
A
T
O
Fan
G
Y2
W2/E
T
H
E
120 VAC
Transformer
Hot
24 VAC
R
M
O
S
T
A
Compressor
Fault Output
(24VAC)
Compressor
Contactor
Reversing
T
Control
Second
Stage Cool
Aux/Emer
NOTE: Make sure the HP swtich is in the HP
position. When switched to HP mode
W1 is connected internally to Y1.
NOTE: Make sure the HP swtich is in the HP
position. When switched to HP mode,
W1 is connected internally to Y1.
6
TERMINAL LEGEND - 8425
TERM EQUIPMENT TO CONNECT REQ? TERMINAL FUNCTION
R 24 VAC hot connection Yes For input of 24VAC hot
C 24 VAC common connection Yes For input of 24VAC
L System fault indicator No For connection of system
connection fault indicator (if present)
W1 First stage connection for No* Energizes on a call
non heat-pump applications for heat
Y2 Second stage cooling No Energizes on a call for
connection second stage cooling
Y1 First stage compressor Yes Energizes on a call for
connection first stage of heating
W2/E Second stage heat or Yes* Energizes on a call for
Emergency heat connection second stage or
B Heat active reversing Yes** Energizes when in the
valve connection HEAT or EM modes
O Cool active reversing Yes** Energizes when in the
valve connection COOL mode
G Indoor fan connection Yes Energizes with E & Y1, Y2
* Do not connect W1 in heat pump applications. Connect auxiliary heat to W2/E.
** Most heat pump systems will have a cool active or a heat active reversing valve. Use the
appropriate terminal.
side of transformer
common side of
transformer
and cooling
emergency heat
and W2 terminals or with
FAN option switched to
the ON position
°
F
GOB Y1W1
C
R
L
ELEC GAS
NON_HP HP
Y2
W2/E
HP OPTION SWITCH
ELECTRIC/GAS SWITCH
Heat pump switch.
Selects fan control.
Figure 5
15. Set the Electric/Gas switch to either GAS for a gas/oil heating
system or ELEC for an electric heating system (Figure 5).
16. Set the HP option switch to either the HP for heat pump or
NON_HP for furnace applications (Figure 5).
17. Replace thermostat cover by snapping into place.
7
Step 3: Testing the Thermostat
emer heat off cool
emer heat off cool
emer heat off cool
emer heat off cool
auto on
auto on
emer heat off cool
!
WARNING: DO NOT SHORT (JUMPER) ACROSS TERMINALS OF GAS
VALVE OR SYSTEM CONTROL TO TEST OPERATION. THIS WILL
DAMAGE THE THERMOSTAT AND VOID YOUR WARRANTY.
CAUTION: DO NOT SWITCH SYSTEM TO COOL OR LEAVE IN COOL MODE
1. Place the EMER-HEAT-OFF-COOL switch into
2. Press the button until the temperature
NOTE: ONCE THE THERMOSTAT TURNS OFF WHEN IN THE COOL MODE,
3. Put the EMER-HEAT-OFF-COOL switch into the
4. Put the EMER-HEAT-OFF-COOL switch into the
5. Press the button until the temperature
NOTE: If HP is selected, the heat will not come on until the 5 minute
6. Put the EMER-HEAT-OFF-COOL switch into the
7. Press the button until the temperature
8. Put the EMER-HEAT-OFF-COOL switch into the
9. Put the AUTO-ON switch into the ON position.
IF THE TEMPERATURE IS BELOW 50°F (10°C). THIS CAN
DAMAGE THE AIR CONDITIONING SYSTEM AND CAUSE PERSONAL INJURY.
the COOL position. The will be displayed.
setting is at least 3 degrees below the room temperature. The air
conditioning system should turn on within a
few seconds.
A BUILT IN 5-MINUTE DELAY PREVENTS THE SYSTEM FROM
TURNING ON AGAIN. THIS PROTECTS THE COMPRESSOR. NO
ADDITIONAL TIME DELAY RELAY IS REQUIRED. TO OVERRIDE THE
5-MINUTE DELAY FOR INSTALLATION, PRESS THE RESET BUTTON.
OFF position. The air conditioning system
should turn off.
HEAT position. The will be displayed.
setting is at least 3 degrees above room
temperature. The heating system should turn on. The fan may
not turn on immediately, depending on the fan delay built into
the furnace.
short cycle protection has expired.
EMER position. The will be displayed.
setting is at least 3 degrees above room
temperature. The secondary heating system should turn on.
NOTE: The compressor will not turn when in
emergency heat mode.
OFF position. The heating system should turn
off. The fan may continue to run for a short
period of time.
The blower fan should turn on. The display will show
a .
10. Put the AUTO-ON switch into the AUTO position.
The blower fan should turn off.
8
Step 4: Customizing the Thermostat
♦ Settings
System
Cool: The thermostat controls the cooling.
Off: The heating and cooling systems are off.
Heat: The thermostat controls the heat.
Emer:The thermostat controls the second stage emergency heat. Use
only when the primary stage of heat is not functioning or requires
service. The display will show CHECK HP
when the heat pump requires service.
Fan
Auto: Equipment controls the fan.
On: The fan operates continuously.
♦ Temperature Differential
The temperature differential for 1ststage is factory set at 1.0°F (.5°C).
This means that whenever the room temperature changes by one
degree Fahrenheit from the temperature setting, the system will turn on.
If the system turns on too often, increase the temperature differential.
NOTE: The temperature differential for 2ndstage is factory set at
2.0°F (1.0°C)
♦ Changing Fahrenheit (°F) to Celsius (°C),
the Temperature Differential, and
the Filter Monitor
1. The thermostat is preset to display the
temperature in degrees Fahrenheit (US
models) or degrees Celsius (Canadian
models). The temperature display can be
changed. Press and hold both the
and buttons for three seconds. The display will flash either
an F or C. Release buttons. Press the or button to switch
the display.
2. Wait five seconds or press and the display will switch to the differential setting for 1
3. The display will read diFF.
Press the or button to adjust the
differential up or down.
4. Wait five seconds or press and the
display will switch to the differential
setting for 2
5. The display will read diF2.
Press the or button to adjust the differential up or down.
6. Wait five seconds or press and
the display will switch to the
differential delay.
7. The display will read dLY2.
The differential delay is the length of time
(in minutes) from when the 1st stage
engages, until the 2nd stage engages to
assist in heating or cooling. Press the or
button to adjust the delay up or down.
nd
st
stage heating and cooling.
stage heating and cooling.
9
8. Wait five seconds or press and the display will switch to the filter monitor setting.
9. CHECK FILTER and the length of hours for
the filter monitor will be displayed.
10. Use the or to adjust the filter timer
from 0 (OFF) to 9900 hours. NOTE: The
filter timer is based on equipment run
time. Select the length of time based on the recommended service
interval for your filter.
11. Press the to return to normal operation.
♦ Check Filter Reset
Once the filter timer has expired,
CHECK FILTER will turn on and stay
on. To clear the message and reset
the timer:
1. Press the and buttons and
hold for 3 seconds. CLr will appear
in the time display.
2. Press any key to clear the message.
The display will transition to the
temperature scale display as
described in the previous section.
3. No further input is needed. Within a few seconds, the display will
return to the normal operating mode.
♦ Backlit Display
This thermostat is equipped with a backlight to make night time temperature adjustments quick and easy. Press the button to activate the
backlight. The backlight will turn off after about 10 seconds of inactivity.
♦ Reset
To reset the thermostat press the RESET button located above the upper
left corner of the display.
RESET switch
°
F
Y2
W2/E
GOB Y1W1
C
R
L
ELEC GAS
NON_HP HP
10
Step 5: Troubleshooting
Symptom Remedy
Thermostat does not turn on system.
Thermostat turns system on and
off too frequently.
System fan does not operate
properly.
Thermostat does not display
proper room temperature.
Check wiring (see Installation
section).
Increase temperature differential
(see Changing the Temperature
Differential section).
Move Electric/Gas switch to
either gas or electric, to match
system (see Installation section).
Check F/C (Fahrenheit/Celsius)
setting. See Changing Fahrenheit
(F) to Celsius (C).
If problems with thermostat cannot be resolved, call:
Technical Support: (800) 445-8299
Monday-Friday 7:30 AM - 5:30 PM CST
For after hours service, a 24-hour automated
help line is available.
11
Two Year Limited Warranty
Invensys Controls Americas warrants to the original contractor
installer, or to the original consumer user, each new Robertshaw
thermostat to be free from defects in materials and workmanship under
normal use and service for a period of two (2) years from date of
purchase. This warranty and our liability does not apply to batteries or
merchandise that has been damaged by misuse, neglect, mishandling,
alterations, improper installation, or use in a way other than in
accordance with Invensys Controls Americas recommendations
and instructions.
Invensys Controls Americas agrees to repair or replace at its option any
thermostat under warranty provided it is returned within the warranty
period, postage prepaid, with proof of the date of purchase. Cost of
thermostat removal or reinstallation is not the responsibility of Invensys
Controls Americas.
Repair or replacement as provided under this warranty is the exclusive
remedy of the consumer. Invensys Controls Americas shall not be liable
for any incidental or consequential damages for breach of any express
or implied warranty on this product, or under any other theory of liability.
Except to the extent prohibited by applicable law, any implied warranty
of merchantability or fitness for a particular purpose on this product is
limited to the duration of this warranty.
Some states do not allow the exclusion or limitation of incidental or
consequential damages, or allow limitations on how long an implied
warranty lasts, so the above limitations or exclusions may not apply to
you. This warranty gives you specific legal rights, and you may also have
other rights which vary from state to state.
For warranty returns, send thermostat, shipping prepaid to:
Invensys Controls Americas
Warranty Claims Department
515 S. Promenade
Corona, CA 92879-1736
Controls Americas
191 E. North Avenue
Carol Stream, Illinois 60188
United States of America
©2005 Invensys Controls Americas 110-1090B
12
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