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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 8401 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 HEAT-OFF-COOL in OFF position (Figure 2).

3. Place 

AUTO-ON switch into AUTO position (Figure 2).

3

Figure 1

heat off cool

auto  on

°

F

Figure 2

heat off cool

auto  on

°

F

!

110-1087B.qxd  3/4/05  4:00 PM  Page 3

Summary of Contents for 8401

Page 1: ...ctric heating and cooling systems or single stage heat pump The 8401 requires the use of a common wire Features Large backlit display Adjustable temperature differential 1 F to 3 0 F 0 5 C to 1 5 C 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...

Page 2: ...rcury 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 80...

Page 3: ...ng wiring does not directly match the labels 4 Remove existing thermostat base from wall Step 2 Installing Model 8401 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 ...

Page 4: ...an 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 matchin...

Page 5: ...COOL 4 WIRE SINGLE TRANSFORMER Fan Control 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 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 Wiring Diagrams ...

Page 6: ...E R M O S T A T NOTE Make sure the HP switch is in the HP position When switched to HP mode W1 is connected internally to Y1 Reversing Valve Fan Relay C R Hot Transformer 24 VAC 120 VAC HEAT PUMP WITH HEAT ACTIVE REVERSING VALVE W1 T H E R M O S T A T NOTE Make sure the HP switch is in the HP position When switched to HP mode W1 is connected internally to Y1 Compressor Contactor Y1 G O B Reversing...

Page 7: ...nection C 24VAC common connection Yes For input of 24VAC common side of transformer W1 Heat connection Yes Energizes on a call for heating Y1 Compressor Connection Yes Energizes on a call for cooling B Heat active reversing valve No Energizes when in the HEAT mode O Cool active reversing valve No Energizes when in the COOL mode G Indoor fan connection Yes Energizes with Y1 W1 terminals or with FAN...

Page 8: ...LAY IS REQUIRED TO OVERRIDE THE 5 MINUTE DELAY FOR INSTALLATION PRESS THE RESET BUTTON 3 Put the HEAT OFF COOL switch into the OFF position The air conditioning system should turn off 4 Put the 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 ...

Page 9: ...renheit 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 3 The display will read diFF The tempera ture differential is factory s...

Page 10: ... 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 pres...

Page 11: ...urs service a 24 hour automated helpline is available Thermostat turns system on and off too frequently Increase temperature differential see Changing the Temperature Differential section System fan does not operate properly Move Electric Gas switch to either gas or electric to match system see Installation section Thermostat does not display proper room temperature Check F C Fahrenheit Celsius se...

Page 12: ...air 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...

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