Optional Supply Static Pressure Sensor; Optional Enthalpy Sensor; Optional Economizer Differential Pressure Sensor; Low Ambient Fan Control (S11 And S84) - Lennox Prodigy 2.0 Application Manual

4.5.

Optional Supply Static Pressure Sensor

The supply duct differential static pressure sensor (A30) is an analog sensor with a 0-10VDC output over a range of 0-5"w.c
as shown in the following table. The sensor is powered with 24VAC.
Pressure "w.c. DC Voltage
0 0
0.5 1
1 2
4.6.

Optional Enthalpy Sensor

The optional enthalpy sensors (A7 and A63) used with the economizer have an output of 4-20mA. The sensor is powered
with 18VAC provided by M3 Unit Controller (see figure 9 on page 39).
4.7.

Optional Economizer Differential Pressure Sensor

Rooftop units installed with Smart Airflow™ will have a Pressure Transducer (PT5) present in the economizer. PT5 requires
5VDC power supply (P266-5 and {P266-6) and gives 0.25 VDC to 4 VDC output (P266-4) corresponding to 0" water column
and 2" water column respectively. For all practical purposes the output should be less than 1.2" water column if not an error
code is stored and service alarm output is turned on.
5. Low Ambient Fan Control (S11, S84, S85 and S94)
See table 11 for fan layouts and tables 12 through 18 for low ambient fan operations.
5.1. High Efficiency A Box (3 - 5 Ton)
The outdoor fan in a high efficiency A Box unit operates at three distinct speeds; High, Low and Extra-low. At higher outdoor
temperatures, (above 65°F), the fan operates at high speed for a high cooling demand and at low speed for a low cooling or
de-humidification demand. At low outdoor temperatures the fan is off until the liquid pressure switch, S11 closes. Then the
fan runs at extra-low speed. See unit installation instruction or service manual for specific operational details.
5.2. Standard Efficiency A Box (3 - 5 Ton) and High Efficiency 6-Ton
During low ambient conditions, the outdoor fan is cycled by liquid line pressure switch S11. The M3 Unit Controller will also
de-energize fan due to low outdoor temperature. See unit installation instruction or service manual for specific operational
details.
5.3. Ultra-High Efficiency B Box
The following is the sequence of operations for the outdoor fans during low ambient conditions:
•
Low ambient operations will be activated based on the Parameter 84 (Low Ambient Outdoor Air Limit Temperature 2
Set Point). Factory default setting is 55°F. Go to SETTINGS > RTU OPTION > EDIT PARAMETER = 84 (LAC SP
TEMP 2)
•
Low ambient is deactivated when outdoor air temperature exceeds Parameter 84 + 3°F.
•
During normal operation all three fans are energized. During low ambient operation, two fans are de energized leaving
a single fan energized. During low ambient operation the fan speed is determined by whether the system is operating
in part load (one fan and one compressor) or full load (one fan and two compressors).
•
During low ambient conditions, if the low ambient pressure switch (S11) opens (240+10 PSIG) the single-fan is
de-energized and re-energized once pressure reaches 450+10 PSIG.
•
When switching back from low ambient to normal operation, the single-fan will be de-energized and then all three fans
will be re-energized simultaneously.
See unit installation instruction or service manual for specific operational details.
5.4.

Other Units

During low ambient conditions, various outdoor fans are cycled by liquid line pressure switches; S11, S84, S85 and S94. The
M3 Unit Controller will also de­energize fans due to low outdoor temperature. See tables 12 through 18 for further details.
Pressure "w.c. DC Voltage
1.5 3
2 4
2.5 5
Page 23
Pressure "w.c. DC Voltage
3 6
3.5 7
4 8
Pressure "w.c. DC Voltage
4.5 9
5 10