Carrier 33CSSP3-FC - Phasing Problems and Auxiliary Control

About Advanced Features & Operation
32
SINGLE SETPOINT BEHAVIOR - When congured for Single Setpoint operation (step
#4, page 19), the degree icon will blink when the large number is displaying room
temperature and will remain solid when displaying the heating or cooling setpoint.
In the Auto mode the deadband is enforced both above and below the setpoint. To
avoid short cycling, a deadband of at least two degrees is recommended (step #8,
page 20). To display the room temperature press and hold the MODE button for two
seconds. Release the MODE button to return to the normal display.
Auxiliary Input Control and Multiple HVAC Control
Potential Phasing Problems
Whenusingtheauxiliaryinput(CK1&R)orcontrollingmultipleHVACunitswitha
single thermostat, it is possible to encounter transformer phasing problems that will
interfere with thermostat operation. Connecting transformers that are not phased
correctly may result in a direct short, which could damage transformers and/or the
thermostat. Phasing problems are likely if the units share a common ground with
secondary grounded transformers.
SOLUTION: If possible, phase all HVAC units together. If phasing is impractical,
isolation relays may be used to isolate the transformers. To isolate the auxiliary
input, use a separate transformer for the auxiliary control device, usually a time clock.
Connect the device to an isolation relay coil. Connect one set of isolated contacts to
each thermostat at CK1 and R. See diagram A.
Diagram A- Auxiliary Control
110vac Isolation Relay
Coil
CK 1
R
Thermostat
CK 1
R
Thermostat
CK 1
R
Thermostat
Additional relays may be used. Relay coils must be wired in parallel.
CAUTION WARNING
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