To Use An Auxiliary Control Power Transformer - Carrier RTU Open v3 Installation And Startup Manual

To use an auxiliary control power transformer

If you use a separate control power transformer, it is essential that the auxiliary transformer and the rooftop
transformer are in-phase. You must verify this prior to connecting the auxiliary transformer to the RTU Open.
Follow these steps:
1
Verify the available primary voltage at the rooftop equipment.
2
Remove power from the rooftop equipment and install the appropriate auxiliary transformer. Follow the
manufacturer's installation instructions.
3
Ground one leg of the auxiliary transformer's secondary wiring.
4
Apply power to the rooftop equipment. Measure the potential between the rooftop equipment control power
and auxiliary transformer's secondary hot (non-grounded) legs. If the voltage measured is less than 5 volts,
the transformers are in-phase; proceed to step 7. If you measure a voltage greater than 24 Vac, then the
phases are reversed.
5
Correct the phase reversal by either of the following methods:
Remove the ground from the secondary at the auxiliary transformer and connect it to the other
○
secondary
Reverse the primary wiring at the auxiliary transformer
○
6
Repeat step 4 to rewire.
7
Remove connector assembly from RTU Open's J1 connector.
8
Connect the auxiliary transformer wires to J1 wires 1 (24 Vac) and 3 (Gnd).
9
Apply power to the transformer.
10 Measure the voltage at the RTU Open's J1 - 1 and 3 to verify that the voltage is within the operating range of
21.6–26.4 Vac.
11 Attach harness to RTU Open's connector J1. See illustration below.
NOTE The harness connectors are keyed and must be oriented properly for correct installation.
12 Verify that the Power LED is on and the Run LED is blinking.
RTU Open v3
Installation and Start-up Guide
9
Installing the RTU Open
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