LAT & LED's Questions:

10.1
Q.
 What does the "LAT" control do?
A.
 The LAT controls the desired heating and cooling temperature range within the supply duct.
10.2
Q.
 Why should I use the "LAT" control?
A.
 The "LAT" control is a plus in several respects:
  • Provides high & low secondary temperature protection to the HVAC equipment.
  • Eliminates freeze up of evaporator coil.
  • Can de-energize second stage Heat or Cool, and eliminate the over conditioning of supply air.
  • Can aid in the reduction of excessive residual cooling and heating after a small zone cycle.
10.3
Q.
 How shall I select the right temperature?
A.
 You must set the LAT control setting BELOW your HVAC equipment primary factory protection level for heating. To set for Htg, use equipment manufacturer maximum temperature rise plus the average return air temperature.  For Clg, set the LAT above the manufacturer's factory protection level, between 40°F and 46°F.

NOTE: All LAT limit controls are to be used as secondary controls only.
10.4
Q.
 What range of settings are available on the "LAT"?
A.
 The LAT settings range from 100°F to 180°F for heating and from
40°F to 56°F for cooling.  Both heating and cooling also have an Off setting.
10.5
Q.
 Where do I install the "LAT" control?
A.
 Place the LAT downstream from the AC coil and heat exchanger. Preferably in a trunk line common to all zones approximately 12" to 24" from the plenum.
10.6
Q.
 What do the Red LED's near the "LAT" rotary switches mean?
A.
 When the Red LED's illuminate, one or both stages of heat (gas valves for a furnace or compressor for a heat pump) has been shut off because the high limits have been reached.  The lower Red LED (labeled #2) will illuminate when the duct temperature reaches 10°F below the high LAT setpoint.  The upper Red LED (labeled #1) will illuminate when the duct temperature reaches the high LAT setpoint.
10.7
Q.
 What do the Yellow LED's near the "LAT" rotary switches mean?
A.
 When the Yellow LED's illuminate, one or both stages of cooling (compressors) have been shut off because the low limits have been reached. The lower yellow LED (labeled #2) will illuminate when the duct temperature reaches 5°F above the low LAT setpoint. The upper Yellow LED (labeled #1) will illuminate when the duct temperature reaches the high LAT setpoint.
10.8
Q.
 How do I know if the "LAT" Sensor has a fault or is damaged?
A.
 If the sensor fails, the zone panel will shut down the HVAC equipment and either both Red A1 & A2 LED's or both Yellow B1 & B2 LED's will flash continually.

All AB model chips stamped V 1.0 and V 2.0:

  • A1: If the Red LED's are flashing, the sensor is reading an open (infinite ohms) across the LAT terminals.
  • B1: If the Yellow LED's are flashing, the sensor is reading a shorted sensor (0 ohms) across the LAT terminals.

V 3.0 chip and higher:

  • A2: If the Red LED's flash when serving a Heat (W1) call, the sensor circuit is reading an open (infinite ohms) across the LAT terminals.
  • B2: If the Yellow LED's are flashing when serving a Cooling call, the sensor circuit is reading a shorted sensor (0 ohms) across the LAT terminals.

(Check for loose or shorted wires at LAT terminal connection)
10.9
Q.
 How do I connect the Leaving Air Temperature Sensor, "LAT" to the Zoning System?
A.
 Connect the two leads to the two LAT Terminals on the right-hand side of the panel.  Connect the green "ground" wire to the ground terminal located in the upper left corner of the board. If you need additional wire length to place the sensor where you need it, you can add up to 100 ft. of wire. We recommend using a two conductor 18 gauge cable for extending the LAT sensor.

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