R8845U UNIVERSAL SWITCHING RELAY
© 2020 Resideo Technologies, Inc. All rights reserved.
This product is manufactured by Resideo Technologies, Inc. and its affiliates.
www.resideo.com
Resideo Technologies, Inc.
1985 Douglas Drive North, Golden Valley, MN 55422
1-800-468-1502
68-0215—02 M.S. Rev. 07-21 | Printed in United States
Fig. 9. R8845U control options.
OPERATION
The R8845U consists of a transformer, two Spst line voltage
relays, a Spst low-voltage relay and wiring terminals. When
line-voltage is applied to the transformer, the relay is
powered on thermostat contact closure. The relay may also
be used to provide electrical isolation in low-voltage circuits,
if powered from a 24 Vac or 24 Vdc external source
connected to W(T) and C. Fiber barriers separate line- and
low-voltage connections.
CHECKOUT
1.
Keep the cover on the relay during normal operation
and remove only for service and checkout.
2.
Relay contacts require no cleaning; they are arranged
to close with a wiping action and are self-cleaning. The
contacts may turn black after being in service for some
time; this discoloration does not prevent proper opera-
tion.
3.
After installation is complete, operate system through
at least one cycle from the controller to make certain
the relay controls the equipment as intended.
TROUBLESHOOTING
Test Button
This connection is the same as a call for heat connection
between the R(T) and W(T) terminals.
Heat Call LED
• The LED should light if there is a call for heat or if the test
button is pressed.
• If the LED remains off during a call for heat and turns on
when the Test Button is pressed, the thermostat is not
operating correctly.
• If the LED remains off on a call for heat and also remains
off when the Test Button is pressed, the R8845U is not
operating correctly. Check the fuse; if the fuse is intact,
replace the control.
Relay LED
This LED lights whenever there is 120 Vac (L1) on the N.O.
terminal (when COM/N.O. relay contacts are closed).
L1
L2
COM
R(T)
A
N.O.
C
W(T)
R8845U
M13320
A.
FOR 24V THERMOSTAT CONTROL
R
C
W
THERMOSTAT
B.
FOR LINE VOLTAGE CONTROL
C. FOR EXTERNAL SEPARATE LOW VOLTAGE POWER SOURCE
OPTIONAL
L1, (HOT)
NEUTRAL
LINE VOLTAGE
CONTROLLED
OUTPUTS
X2
X1
LOW VOLTAGE POWERPILE®
CONTROLLED OUTPUT
L1
L2
C
R8845U
JUMPER
LINE VOLTAGE
CONTROL
NEUTRAL
X2
X1
L1
L2
C
R8845U
NEUTRAL
X2
X1
24V CONTROLLER
INPUT SUPPLY
1
REQUIRED FOR OUTPUT LED OPERATION.
2
FOR SERIES 10 OR OTHER HARDWIRED ELECTRONIC 3-WIRE
THERMOSTATS.
3
WARNING!
ELECTROCUTION HAZARD. POWER SUPPLY CAN
CAUSE SEVERE INJURY OR DEATH. DISCONNECT POWER BEFORE
WIRING OR SERVICING L1. POWERED RELAYS MUST BE WIRED AS
DRY CONTACTS.
B
COM
A
N.O.
B
COM
A
N.O.
B
R(T)
W(T)
R(T)
W(T)
1
2
3
