Trane INTELLIPAK ™ ™ ™ ™ ™ Commercial Single-Zone Rooftop Air Conditioners with CV or VAV Control - Manual (Page 9)

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General Information (Continued)
3S69 is a binary input device used on all rooftop units
equipped with an exhaust fan. It is located in the exhaust
fan section of the unit and is connected to the RTM (1U48).
During a request for fan operation, if the differential switch
is detected to be open for 40 consecutive seconds, the
economizer is closed to the minimum position setpoint, the
request for exhaust fan operation is turned "Off" and locked
out, and a manual reset diagnostic is initiated. The fan fail-
ure lockout can be reset; at the Human Interface located in
the unit's control panel, by Tracer, or by cycling the control
power to the RTM (1S70 Off/On).
Lead-Lag
Is a selectable mode of operation on 40 thru 130 Ton units
within the Human Interface. It alternates the starting be-
tween the first compressor of each refrigeration circuit. Only
the compressor banks will switch, not the order of the com-
pressors within a bank, providing the first compressor in
each circuit had been activated during the same request for
cooling.
Supply and Exhaust Fan Circuit Breakers (1CB1, 1CB2)
The supply fan and exhaust fan motors are protected by cir-
cuit breakers 1CB1 and 1CB2 respectively. They will trip
and interrupt the power supply to the motors if the current
exceeds the breaker's "must trip" value. The rooftop module
(RTM) will shut all system functions "Off" when an open fan
proving switch is detected.
Low Pressure Control
Is accomplished using a binary input device on CV & VAV
applications. LP cutouts are located on the suction lines
near the scroll compressors.
The LPC contacts are designed to close when the suction
pressure exceeds 22 ± 4 psig. If the LP control is open
when a compressor is requested to start, none of the com-
pressors on that circuit will be allowed to operate. They are
locked out and a manual reset diagnostic is initiated.
The LP cutouts are designed to open if the suction pressure
approaches 7 ± 4 psig. If the LP cutout opens after a com-
pressor has started, all compressors operating on that cir-
cuit will be turned off immediately and will remain off for a
minimum of three minutes.
If the LP cutout trips four consecutive times during the first
three minutes of operation, the compressors on that circuit
will be locked out and a manual reset diagnostic is initiated.
Saturated Condenser Temperature Sensors (2RT1 and
2RT2)
Are analog input devices used on CV & VAV applications
mounted inside a temperature well located on a condenser
tube bend. They monitor the saturated refrigerant tempera-
ture inside the condenser coil and are connected to the
SCM/MCM (1U49). As the saturated refrigerant temperature
varies due to operating conditions, the condenser fans are
cycled "On" or "Off" as required to maintain acceptable op-
erating pressures.
Head Pressure Control
is accomplished using two saturated refrigerant tempera-
ture sensors on CV & VAV applications. During a request
for compressor operation, when the condensing tempera-
ture rises above the "lower limit" of the controlband, the
Compressor Module (SCM/MCM) starts sequencing con-
denser fans "On". If the operating fans can not bring the
condensing temperature to within the controlband, more
fans are turned on. As the saturated condensing tempera-
ture approaches the lower limit of the controlband, fans are
sequenced "Off". The minimum "On/Off" time for condenser
fan staging is 5.2 seconds. If the system is operating at a
given fan stage below 100% for 30 minutes and the satu-
rated condensing temperature is above the "efficiency
check point" setting, a fan stage will be added. If the satu-
rated condensing temperature falls below the "efficiency
check point" setting, the fan control will remain at the
present operating stage. If a fan stage cycles four times
within a 10 minute period, the control switches from control-
ling to the "lower limit" to a temperature equal to the "lower
limit" minus the "temporary low limit suppression" setting. It
will utilize this new "low limit" temperature for one hour to
reduce condenser fan short cycling.
High Pressure Controls
High Pressure controls are located on the discharge lines
near the scroll compressors. They are designed to open
when the discharge pressure approaches 405 ± 7 psig. The
controls reset automatically when the discharge pressure
decreases to approximately 300 ± 20 psig. However, the
compressors on that circuit are locked out and a manual re-
set diagnostic is initiated.
Outdoor Air Humidity Sensor (3U63)
Is an analog input device used on CV & VAV applications
with 100% economizer. It monitors the outdoor humidity lev-
els for economizer operation. It is mounted in the fresh air
intake section and is connected to the RTM (1U48).
Return Air Humidity Sensor (3U64)
Is an analog input device used on CV & VAV applications
with the comparative enthalpy option. It monitors the return
air humidity level and compares it to the outdoor humidity
level to establish which conditions are best suited to main-
tain the cooling requirements. It is mounted in the return air
section and is connected to the ECEM (1U52).
Low Ambient Control
The low ambient modulating output on the compressor
module is functional on all units with or without the low am-
bient option. When the compressor module has staged up
to it's highest stage (stage 2 or 3 depending on unit size),
the modulating output will be at 100% (10 VDC). When the
control is at stage 1, the modulating output (0 to 10 VDC)
will control the saturated condensing temperature to within
the programmable "condensing temperature low ambient
control point".
Status/Annunciator Output
Is an internal function within the RTM (1U48) module on CV
& VAV applications that provides;
a. diagnostic and mode status signals to the remote
panel (LEDs) and to the Human Interface.
b. control of the binary Alarm output on the RTM.
c. control of the binary outputs on the GBAS module to
inform the customer of the operational status and/or
diagnostic conditions.