Carrier RTU Open v3 - To Use the Rooftop Equipment Control Power Transformer

Installing the RTU Open
RTU Open v3 CARRIER CORPORATION ©2019
Installation and Start-up Guide All rights reserved
8
• Avoid running communication wires or sensor input wires next to AC power wires or the controller's relay
output wires. The resulting noise can affect signal quality. Common sources of noise are:
○ Spark igniters
○ Radio transmitters
○ Variable speed drives
○ Electric motors (> 1hp)
○ Generators
○ Relays
○ Transformers
○ Induction heaters
○ Large contactors (i.e., motor starters)
○ Video display devices
○ Lamp dimmers
○ Fluorescent lights
• In most cases, the RTU Open will be powered from the control power transformer provided with the rooftop
equipment. If you must use a separate control power transformer, additional precautions must be taken to
ensure that the auxiliary transformer is in-phase with the rooftop equipment’s control power transformer. See
Using an auxiliary control power transformer (page 9).
To use the rooftop equipment control power transformer
1 Remove power from the 24 Vac transformer.
2 Remove connector assembly from RTU Open's
J1
connector.
3 If the rooftop equipment has thermostat connection terminals, connect wiring harness
J1
wire 1 to R, and
J1
wire 3 to C. Alternately, connect the control power transformer wires to
J1
connector wires 1 (24 Vac) and 3
(Gnd).
4 Apply power to the rooftop equipment.
5 Measure the voltage at the RTU Open’s
J1
terminals 1 and 3 to verify that the voltage is within the operating
range of 21.6–26.4 Vac.
6 Attach harness to RTU Open connector
J1
.
NOTE
The harness and connector are keyed and must be oriented properly for correct installation.
7 Verify that the
Power
LED is on and the
Run
LED is blinking.