HVAC definitions of TLC and PTU

Hi,
I've just come from posting my question at alt.HVAC where I got all kinds of 'cute' definitions on what TLC and PTU might stand for. The most intelligent response I got from that group was to try posting my question here.
Could someone give me the HVAC definitions for 'TLC and PTU' when used for a gas mid-efficient furnace?
The reason I ask is my daughter's 1993 Lennox G24M2-75A-2 mid-efficient hot surface ignitor furnace has been (IMHO) rapidly cycling lately.
I came across a service bill at her home from many years ago (before they bought the home) and it had the notation 'Recommend TLC or PTU'.
So I was thinking - maybe TLC means: Temperature Limit Control? But PTU? . . . They had their ducts cleaned in the summer - but the furnace was not cleaned at that time. I'm going to recommend that they have the furnace cleaned but was wondering if the TLC or PTU might also require attention (provided I can figure out what they are).
The furnace has the normal pre-ignition exhaust fan run for 1 minute then normal ignition but the gas runs for only for 4 minutes (which seems a short period of time to me at least compared to my furnace) The blower fan starts normally after the 1 minute heat exchanger warm up period, After the gas shuts off, the blower runs for the cool down period for 3 minutes to fan off There is a 2 minute delay - which seems abnormally short - then the ignition sequence restarts.
Total cycle time 10 minutes.
They have been doing lots of renovations - some involving work around the ducts & I suspect they may have kicked up a lot of dust onto the heat exchanger.
We replaced the blower compartment filter. The problem persists.
Thanks, Cindy
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Sometimes it can mean Tender Loving Care or Precision Tune Up. Or:
http://www.thermometrics.com/assets/images/ptu.pdf
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