Problem inspecting a Lennox

More often than not, by pulling a slammed filter out, you are actually saving your customer from having to call an HVAC tech for a service call that might cost them hundreds of dollars. This is especially true when the house has undergone recent carpet replacement or drywall repair or interior spray painting. If the power is on when these crews are in there doing one of these dusty jobs, you can bet they’ll be taking advantage of the heating or cooling… And if you do find one that is slammed, it’s best to take it out, show the customer how to replace it (if they don’t have any new filters onsite) and advise them to leave the old filter out of the unit until they get a new one today or tomorrow (or whenever). A slammed filter blocks the transfer of heat to the evaporator coil’s vaporized refrigerant, allowing refrigerant to return to the compressor as more of a colder liquid instead of a warmer gas. This will destroy the compressor crankcase bearings in a matter of time, as the compressor oil is displaced from the crankcase and made to circulate throughout the lines and system until the oil eventually migrates back to the crankcase.

I hear that if you flip them over when they’re like that, they breathe much better

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Dirty filters are best with 3 pimento olives - for the record. If they are merely dirty, I put them back in - I’ve suffered the wrath of sellers for leaving them out. If they’re dished or looking like an alley cat, I’ll leave them out with a note for the seller.

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after reading all. one small point killing power by service switch, what would happen if power went out. cut power should not do it

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Exactly, Steve. That’s why the disconnect is there at the unit: so you don’t have to depower the t’stat first, when opening the air handler for whatever reason. Digital and analog t’stats alike were built so they would reset and run automatically when power is restored. You just have to keep in mind that the digital t’stat can revert to the factory default settings- and especially so, if it doesn’t have batteries as a backup power source to retain the newest user settings.

Steve as a past HVAC tech, the service switch is at the unit SO a tech can set it to heat or cool at the t-stat in the house … go to the basement, attic, crawl, etc … check the unit out, service or repair it by turning off the service switch WITHOUT crawling back out of the attic, crawl or basement to do so.

Some units when turned off at the service switch OR if the door interlock is disengaged WILL require reset at the tstat BUT do not cause the unit to kill the tstat.


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Yes that was my point. I’m also HVACR

There is absolutely nothing you can do to damage the t-stat when turning off the power (under any sequence), unless you short out a wire on the control circuit (ie.removing wire nuts, or shorting a terminal to ‘common’).

As for dirty filters; I am currently looking for an R22 scroll compressor because a tenant didn’t change a ‘high efficiency’ filter. She figured she bought a better filter and didn’t need to change as often. It flooded the compressor with refrigerant and broke the shaft to the scroll (something that is uncommon in a scroll).
Flooding a scroll generally does not do damage like in a reciprocal, but washing out the oil from the compressor will kill it.

If I see a dirty filter I can’t see through, it stays out.
You should always document this because it may fail as soon as you walk out the door.

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