THX9321 PRESTIGE
®
2.0 AND THX9421 PRESTIGE
®
IAQ WITH EIM
68-0311—02
90
Set Delta T Limits
1.
Press Stage 1 to set the limits and run time (see Fig.
158). Use the saved test data located in the upper right
corner of the screen to set the Delta T Minimum and
Maximum Limits and the Run Time (see Fig. 159).
Fig. 158.
2.
Press the up or down arrows to set the Minimum and
Maximum Limits and the Run Time.
Fig. 159.
3.
Set appropriate Minimum and Maximum Delta T Limits
based on the reading from the equipment test and what
you consider to be unacceptable performance from the
heating and cooling equipment.
4.
When setting the run time, select a setting based on
when Delta T began to stabilize during the equipment
test. In the example shown in Fig. 157 and 159, Delta T
began to stabilize around 10-11 minutes.
5.
Set the limits and run time for all stages of cooling using
steps 1–4 above.
6.
Repeat steps 1–5 above for Heating.
After Delta T Diagnostics Setup is Complete
The thermostat will measure Delta T after the specified run
time, and compare Delta T to the minimum and maximum limits
for each valid cycle. If the system operates below the minimum
limit or above the maximum limit multiple times (see Table 7),
an alert is recorded in the Alerts Log. If configured to do so, an
alert is displayed to the user (Display Delta T Alerts to User,
ISU 13190). The user is alerted by default. For example, if 10
of the last 15 cycles have the same fault, an alert is logged and
the user is alerted.
Advanced Options for Delta T Diagnostics
To set Advanced Options for Delta T Diagnostics, select Yes for
ISU 13015.Then the following advanced options are displayed:
• Delta T Alert Sensitivity (ISU 13180
; Default: 3
)
• Display Delta T Alerts to User (ISU 13190
; Default: Yes
)
• Allow Delta T Diagnostics:
— during humidification (ISU 13020; Default: Yes)
— during dehumidification (ISU 13030; Default: Yes*)
— during ventilation (ISU 13040; Default: Yes)
— only when indoor temperature is within a certain range
(ISUs 13050, 13090, 13130; Default: Always)
— only when indoor humidity is within a certain range
(ISUs 13060,13100, 13140; Default: Always)
— only when outdoor temperature is within a certain range
(ISUs 13070, 13110, 13150; Default: Always)
— only when outdoor humidity is within a certain range
(ISUs 13080, 13120, 13160; Default: Always)
* Default is Yes for Dehumidifiers and A/C with High Speed
Fan. The thermostat does NOT allow Delta T diagnostics dur-
ing dehumidification if it is setup for A/C with Low Speed Fan,
Hot Gas Bypass, or Reheat.
The Delta T Alert Sensitivity is set on a scale of 1–5 in ISU
13180 (1 is the least sensitive; 5 is the most sensitive):
By default, Delta T alerts are displayed to the user, but can be
turned off and on in ISU 13190.
Delta T Alerts
The thermostat uses alerts and diagnostics to provide greater
comfort and efficiency. Alerts and diagnostics can notify
customers when maintenance or service is needed, and
display your contact information to make it easy for them to
reach you.
This tells you if the system is performing above or below
expected standards which would normally go unnoticed, and
may cause unnecessary energy use. It can also detect and
warn about problems early, before heating or cooling
equipment fails.
There are three alerts each for the heating and cooling system.
They occur when:
• the system is not operating
NOTE: The thermostat displays an alert when the sys-
tem does not reach a Delta T of 5 F after the
thermostat calls for a reasonable period of time.
• the system is operating below the minimum Delta T limit
• the system is operating above the maximum Delta T limit
Delta T Alerts are displayed for basic failures including no
heating or no cooling that may be related to bad igniter, bad
flame sensor, bad gas valve, bad draft motor, bad blower, bad
contactor, bad startup capacitor, dead compressor, etc.
Table 7. Delta T Alert Sensitivity (ISU 13180).
Setting
Alert is logged and user is alerted if
1
10 of the last 15 valid cycles have the same fault, or
25 of the last 30 valid cycles have the same fault.
2
10 of the last 15 valid cycles have the same fault, or
20 of the last 30 valid cycles have the same fault.
3
(Default)
5 of the last 5 valid cycles have the same fault, or
10 of the last 15 valid cycles have the same fault, or
15 of the last 30 valid cycles have the same fault.
4
5 of the last 5 valid cycles have the same fault, or
8 of the last 15 valid cycles have the same fault, or
15 of the last 30 valid cycles have the same fault.
5
3 of the last 5 valid cycles have the same fault, or
8 of the last 15 valid cycles have the same fault, or
10 of the last 30 valid cycles have the same fault.
