Robertshaw 8425 User manual

DIGITAL

NON-PROGRAMMABLE

THERMOSTAT

8425

ELECTRIC

GAS

OIL

NeW

2 Heat / 2 Cool

User's Manual

Quick Start

Installation

HEAT PUMP

Application

The Robertshaw 8425 is a multi-stage thermostat designed to control

24 VAC heat pump systems.

Features

• Large backlit display

• Adjustable 1st stage temperature differential: 1.0°F to 3.0°F (0.5°C to

1.5°C)

• Adjustable 2nd stage temperature differential: 1.0°F to 6.0°F (0.5°C to

3.0°C)

• Adjustable 2nd stage delay (10-40 minutes)

• 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

110-1090B

110-1090B.qxd 3/4/05 3:58 PM Page 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 2nd stage cooling circuit

W2, W-U or E W2/E 2nd stage 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.

110-1090B.qxd 3/4/05 3:58 PM Page 2

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.

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).

Figure 1

emer heat off cool auto on

Figure 2

emer heat off cool auto on

110-1090B.qxd 3/4/05 3:58 PM Page 3

4. Remove the cover using a coin or screwdriver (Figure 3). Set aside.

5. Place thermostat against the wall at desired location. Make sure

wires will feed through opening (Figure 4) on base of thermostat.

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.

heat off cool

hold

vac

prog

run/set hold

temp

clock

set

auto on

MON

Figure 3

W2/E

GOB Y1W1

ELEC GAS

NON_HP HP

Figure 4

Mounting Holes

110-1090B.qxd 3/4/05 3:58 PM Page 4

Hot

Heating

Control

Cooling

Control

Transformer T

24 VAC

120 VAC

HEAT/COOL

4-WIRE

SINGLE TRANSFORMER

Fan

Control

W2/E

Hot

Heating

Control

Transformer

24 VAC

120 VAC

HEAT ONLY

2-WIRE

SINGLE TRANSFORMER

W2/E

HEAT/COOL

2 STAGE

Hot

Transformer

24 VAC

120 VAC

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

W2/E

Hot

Heating

Control

Fan

Control

Transformer

24 VAC

120 VAC

HEAT ONLY

SINGLE TRANSFORMER

3-WIRE

W2/E

♦Wiring Diagrams

110-1090B.qxd 3/4/05 3:58 PM Page 5

Hot

Compressor

Contactor

Transformer

24 VAC

120 VAC

HEAT PUMP WITH

COOL ACTIVE

REVERSING VALVE

NOTE: Make sure the HP swtich is in the HP

position. When switched to HP mode,

W1 is connected internally to Y1.

Reversing

Valve

Fan

Relay

W2/E

HEAT PUMP + AUX COOL

COOL ACTIVE

REVERSING VALVE

Hot

Transformer

24 VAC

120 VAC

NOTE: Make sure the HP swtich is in the HP

position. When switched to HP mode

W1 is connected internally to Y1.

W2/E

Compressor

(24VAC)

Fault Output

Compressor

Contactor

Aux/Emer

Heat

Second

Stage Cool

Fan

Control

Reversing

Valve

Hot

Transformer

24 VAC

120 VAC

HEAT PUMP + AUX HEAT

HEAT ACTIVE

REVERSING VALVE

NOTE: Make sure the HP swtich is in the HP

position. When switched to HP mode,

W1 is connected internally to Y1.

W2/E

Compressor

(24VAC)

Fault Output

Compressor

Contactor

Aux/Emer

Heat

Second

Stage Cool

Fan

Control

Reversing

Valve

Hot

Transformer

24 VAC

120 VAC

HEAT PUMP WITH

HEAT ACTIVE

REVERSING VALVE

NOTE: Make sure the HP swtich is in the HP

position. When switched to HP mode,

W1 is connected internally to Y1.

Compressor

Contactor Y1

Reversing

Valve

Fan

Relay

W2/E

110-1090B.qxd 3/4/05 3:58 PM Page 6

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.

W2/E

GOB Y1W1

ELEC GAS

NON_HP HP

Figure 5

TERMINAL LEGEND - 8425

TERM EQUIPMENT TO CONNECT REQ? TERMINAL FUNCTION

R 24 VAC hot connection Yes For input of 24VAC hot

side of transformer

C 24 VAC common connection Yes For input of 24VAC

common side of

transformer

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

and cooling

W2/E Second stage heat or Yes* Energizes on a call for

Emergency heat connection second stage or

emergency heat

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

and W2 terminals or with

FAN option switched to

the ON position

* 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.

ELECTRIC/GAS SWITCH

Selects fan control.

HP OPTION SWITCH

Heat pump switch.

110-1090B.qxd 3/4/05 3:58 PM Page 7

Step 3: Testing the Thermostat

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

IF THE TEMPERATURE IS BELOW 50°F (10°C). THIS CAN

DAMAGE THE AIR CONDITIONING SYSTEM AND CAUSE PER-

SONAL INJURY.

1. Place the EMER-HEAT-OFF-COOL switch into

the COOL position. The will be displayed.

2. Press the button until the temperature

setting is at least 3 degrees below the room temperature. The air

conditioning system should turn on within a

few seconds.

NOTE: ONCE THE THERMOSTAT TURNS OFF WHEN IN THE COOL MODE,

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.

3. Put the EMER-HEAT-OFF-COOL switch into the

OFF position. The air conditioning system

should turn off.

4. Put the EMER-HEAT-OFF-COOL switch into the

HEAT position. The will be displayed.

5. Press the button until the temperature

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.

NOTE: If HP is selected, the heat will not come on until the 5 minute

short cycle protection has expired.

6. Put the EMER-HEAT-OFF-COOL switch into the

EMER position. The will be displayed.

7. Press the button until the temperature

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.

8. Put the EMER-HEAT-OFF-COOL switch into the

OFF position. The heating system should turn

off. The fan may continue to run for a short

period of time.

9. Put the AUTO-ON switch into the ON position.

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.

emer heat off cool

auto on

emer heat off cool

110-1090B.qxd 3/4/05 3:58 PM Page 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 1st stage 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 2nd stage 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 For C. Release buttons. Press the or button to switch

the display.

2. Wait five seconds or press and the display will switch to the dif-

ferential setting for 1st stage heating and cooling.

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 2nd stage heating and cooling.

5. The display will read diF2.

Press the or button to adjust the dif-

ferential 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.

110-1090B.qxd 3/4/05 3:58 PM Page 9

8. Wait five seconds or press and the display will switch to the fil-

ter 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 temper-

ature 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.

W2/E

GOB Y1W1

ELEC GAS

NON_HP HP

RESET switch

110-1090B.qxd 3/4/05 3:58 PM Page 10

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