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THX9321 PRESTIGE
®
2.0 AND THX9421 PRESTIGE
®
IAQ 2.0 WITH EIM
51 68-0311—01
Before You Set Up Delta T
Diagnostics
Refer to the information below for tips on installation and setup
of Delta T Diagnostics.
1. Refer to Fig. 5–9 for the placement of the Discharge and
Return Air Sensors.
2. In gas or oil forced air systems, Delta T will continue to
rise for several minutes even after Delta T begins to
stabilize. Be sure the Maximum Delta T Limit is set
higher than the expected stable Delta T. See Fig. 52.
Fig. 52.
3. Delta T can be affected by indoor and outdoor conditions
for heat pumps and cooling systems. Consider the total
range of normal performance when setting the Delta T
Limits.
For example, in cooling, you might have a Delta T of 20
°F when the outdoor humidity is 50% and a Delta T of 16
°F when the outdoor humidity is 85%.
You can either set Limits further apart and monitor Delta
T during all indoor and outdoor conditions or set Limits
closer together and turn off diagnostics during certain
indoor and outdoor conditions (see “Advanced Options
for Delta T Diagnostics” beginning on page 53).
For example, you can set limits closer together and then
turn off diagnostics when outdoor temperature is above
90 degrees and outdoor humidity is above 85%.
4. Verify the filter is clean and all the registers are open
before running an equipment test.
5. Select a Run Time when Delta T begins to stabilize
during the equipment test.
6. Set Minimum and Maximum Delta T Limits based on
what you consider to be unacceptable performance from
the heating and cooling equipment.
NOTE: When the system operates below the Minimum
Limit or above the Maximum Limit multiple
times (Table 3), an alert is recorded in the log. If
configured to do so, the thermostat will display
an alert to the user, along with your contact
information.
7. Delta T Diagnostics is only for non-zoned forced air
systems.
8. The thermostat does not provide Heat or Cool Delta T
Diagnostics when it is set to control an Economizer
module (ISU 2220).
9. The thermostat cannot be setup for Heat Delta T
Diagnostics when the thermostat is used with an external
fossil fuel kit (ISU 2190).
Setting up Alerts and Diagnostics
1. Set up the Return and Discharge Air Sensors by
selecting the check boxes on the screen. These sensors
are used to measure Delta T.
Fig. 53.
2. Select the terminals that are wired to the Discharge and
Return Air Sensors (terminals S1 and S2 at the EIM).
IMPORTANT
Be sure to select the correct terminals for the dis-
charge and return air sensors. For example, if the
return air sensor is wired to S1, select S1 (see Fig.
54) for the return air sensor.
Fig. 54.
RUN TIME
M31489
DELTA T
MINIMIUM DELTA T LIMIT
RUN TIME WHEN THERMOSTAT
COMPARES DELTA T TO THE
MINIMUM AND MAXIMUM DELTA T LIMITS
DELTA T NOT STABLE DELTA T STABLE
DELTA T BEGINS TO STABILIZE
MAXIMUM DELTA T LIMIT