Robertshaw 8425 User Manual

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