Fluctuation of filter life reading on Infinity t-stat

[BPChiIL]

Fully realizing that the filter life is based on static pressure - why do the percentage readings vary? For instance, one day it will read 60% used and the next day it will read 30% used. The unit itself runs on low stage roughly 90% of the time, therefore, the air flow (static pressure) itself is not varying a great deal.

Thanks in advance for your help / answers!

[isuredo]

True Sense Dirty Filter Detection for (-A) User Interface
At 1:00 PM each day, or when the user switched the system from OFF to any
operating mode, the fan will run at either 233 CFM/ton of cooling capacity or
(90% High Heat Airflow/1.5), whichever is higher for one minute after
heating/cooling is turned off (A heating or cooling call will be interrupted if in
progress at 1:00 PM). If the furnace staging is set to LOW, then use the low
furnace airflow/1.5 or cooling airflow (233 CFM/ton), whichever is highest.
Blower RPM measurements are then taken and a static pressure is calculated.
If the blower has not run in the past 24 hours, the measurement will not be made.
If the system is

[isuredo]

Situation: Clean or Replace Filter is displayed after a short period of time
These systems have a feature called TrueSense filter detection. This feature reads the change in
static pressure caused by the filter accumulating dirt. At 1:00 pm each day the system will take a
reading and record the change in static pressure. The clean or replace filter message will pop up
when the filter is full.
This feature operates by setting a base line static pressure based on the highest airflow the system
could run (this could be heat or cool airflow). The measurement is taken at a low airflow, and then
calculated up to the highest airflow the system could see. An enhancement to the (-A) model was
that if a furnace is used and it is locked in low fire, the calculation will use the higher of the cooling
airflow or low furnace heat airflow. In previous versions, it used the higher of high furnace airflow or
cooling airflow even if the furnace was locked in low fire.
In (-A) models (version 10 and 12 software), clean filter routine was changed to eliminate nuisance
pop up messages when a marginal duct system is used. When the initial static pressure is 0.7
inches or higher, a modified calculation is used to allow this feature to be used at higher static
pressures. With –A models, it will only pop up immediately if the initial static is 1.5 inches or higher.
This truly indicates a ductwork problem that must be addressed.
Options if this pops up quickly:
• Evaluate duct work and make improvements to lower static pressure where possible
• Change filter type to EAC. This will display the message based on time instead of static
pressure change
• Turn the filter reminder to off in the homeowner’s Advance Setup