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Do not touch both probes with your fingers—doing so will produce a faulty reading.
At 77°F, the resistance of the sensor will be 10K ohm; at lower probe temperatures,
expect higher resistance; at warmer probe temperatures, expect lower resistance.
After reading the resistance at room temperature, warm the tip of the sensor by
holding it in the palm of your hand, and take another resistance reading. The
resistance should be noticeably lower than the previous reading.
The zone control system will monitor the operation of the probe and determine
if a failure has occurred. The probe is an integral (but replaceable) part of the
zone control system. The zone control system will indicate if the probe is operating
improperly and needs to be replaced. The discharge air temperature probe serves
several purposes:
1.
In cooling systems (and heat pump systems in cooling mode) the probe varies
the speed of the compressor from high to low to off in order to maintain a
constant discharge air temperature and prevent coil freezing.
2.
In gas heating systems, it is responsible for increasing the speed of the blower
to the setting of the CFM jumpers after the discharge air has warmed up to
about 100ºF. Also stages equipment up and down to control discharge air
temperature.
3.
In heat pump systems operating in the heating mode, the probe varies
compressor speed and stages of auxiliary heat in order to maintain a constant
discharge air temperature.
6.1.5.
Blower Speed Checkout
The indoor blower speed should vary as zone demand changes. The fan speed
LED varies in brightness as the blower varies in speed. The brighter the LED, the
more CFM being delivered. Blower speed can also be viewed by attaching an
electronic voltmeter between
DS
and any
C
terminal on the zone control panel.
While not a precise measurement, the voltmeter fluctuation indicates that the
blower speed is changing.
1.
Connect electronic voltmeter between
DS
and any
C
terminal on the zone
control panel. Leave all field wiring in place.
2.
Select DC volts scale.
3.
Start zone heating or cooling checkout procedure.
4.
Observe voltages:
• 22 volts DC = high speed (varies depending on input voltage at primary
transformer).
• 11 volts DC (approx.) = Medium speed 50% into adjustment band of blower.
• 0 volts DC = low speed or off.
NOTE:
All speeds in between are a percentage of 22VDC.
5.
Also measure voltage at the indoor unit between
DS
and
C
. If the voltage is
lower than the voltage measured at the Harmony zone panel and/or the blower
runs at a minimum fan speed, check and make sure
C
on the indoor unit is
connected to C on the zone panel transformer connection.
NOTE:
SLP98 furnace models are equipped with an LED on the integrated
control which displays blower airflow in all modes of operation. See SLP98
installation instructions for additional information.
NOTE:
CBA38MV, CBX40UHV and CBX32MV Rev 06 or higher have an LED
display that will indicate the unit air volume. “A” followed by the number
indicates the CFM. For example, “A-2-0-0-5” indicates 2005 CFM.
NOTE:
If blower operates only at the minimum CFM or will not ramp to zone air
volume, check and make sure terminal
C
on the indoor unit terminal strip
is connected to Harmony 24 VAC terminal
C
(see figures 17 through 27).
NOTE:
If blower “hunts”, check and make sure there is no connections on Y1 or
Y2 on the indoor unit terminals strip.
NOTE:
Units without a 7-Segment LED will have a “CFM” LED to indicate blower
airflow. One blink of the LED is equal to approximately 100 CFM; then it
pauses and repeats. For example if the CFM indicator LED blinks 10 times
this indicates approximately 1000 CFM.
NOTE:
Make sure DS on the Harmony board is connected to DS on the furnace/
air handler terminal strip.
Summary of Contents for Harmony III
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