Installation - Controls
UNT-SVX07J-EN 83
Heating
In general, the (CSTI) changeover function will provide
heating if:
• A unit is factory-configured with a changeover coil
(cooling/heating) as the only coil or as the main coil
portion.
• SW3 on the CSTI adapter board is turned on, and the
Fprv parameter set to EHl or Ehfs to use the
changeover functions.
–
Ehl parameter should be chosen if the unit has a
changeover coil without electric heat.
–
EhFs parameter should be chosen if the unit has a
changeover coil with electric heat. Generally, this
will perform the same as the
Ehl parameter but will
in addition, disable the heating function on electric
heat and on the changeover coil heat if there are fan
failures. The auxiliary heating coil valve will
continue to respond to customer heating requests.
• The motor control board has sensed that there is hot
water available on the supply/bypass line for the
changeover coil. In this case, “hot” water is
determined if:
– A 10K NTC thermistor (similar to Trane part number
X13790374010) is wired properly to the motor
control board, through the crossover cables and
CSTI adapter boards.
– The input impedance of the thermistor circuit must
be set correctly (the
Aipu parameter should be set
to
in for CSTI units).
– The temperature sensed is higher than the
Ai2b
parameter.
– The
Ai2b parameter is higher than the Ai2M
parameter.
a. The temperature is not in the dead-band between
the
Ai2b parameter and the Ai2M parameter (in
this case, previous state will be retained).
• The customer thermostat is properly hooked up the
input strip 1TB3, and is requesting heating input (V2)
based on the customer heating set point being higher
than the space temperature.
• The heating input on 1TB3 will drive the main
changeover coil IF conditions 1–4 are satisfied, but will
always drive the auxiliary coil valve (if present).
Electric heat will be locked out (where present) if hot
water is available since SW4 will be factory set to “ON”
in these units.
SW4 selects the electric heat lockout function, where we
will lock out the electric heat circuit based on either:
• The presence of hot water in the changeover coil
section (if the
Fprv parameter is set to EHl).
• Abnormal behavior of the fan/s (if the
Fprv parameter
is set to FnSt).
• Or a combination of both the presence of hot water or
abnormal behavior of the fan/s (if the
Fprv parameter
is set to EHFs).
• The preceding three examples depend on the
inference of the motor control board that hot water is
present. In this case, “hot” water is determined if:
– The temperature sensed is higher than the
Ai2b
parameter.
–The
Ai2b parameter is higher than the Ai2M
parameter.
– The temperature is not in the dead-band between
the
Ai2b parameter and the Ai2M parameter (in
this case, previous state will be retained).
– The input impedance of the thermistor circuit must
be set correctly (the
Aipu parameter should be set
to in for CSTI units).
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