Have a Lennox a/c electric unit with propane heat. At first the unit acted like the thermostat was bad so I changed it out to a new digital thermostat. Then I thought the new thermostat was no good as it did not work so I thought it was not compatible with my system so I went and got another digital thermostat and change it. It is compatible with my system and wired correct. The system would not work because it had a bad capacitor so I changed it out and the unit fired right up and cools the house. Now the problem is when you turn the a/c on it cools the house but the temp does not change on the thermostat. It stays around 78-82 and will not go lower to true temp kick off. So for example I turn the unit on and have it at 72 the house is cold but the temp on the thermostat will read 81 after an hour and never show it is actually cooler in the house to kick off. The unit is not freezing up, the blower is working just fine and the house gets cold just that the a/c will not read on the thermostat the true temp to shut off. So for some reason the a/c is not getting the message the house is cool to tell the thermostat to tell the unit to shut off. Anyone out here with any ideas. I have been searching the internet for a week and have come up empty I can not figure out what the issue could be. Has to be something simple but simple is not my middle name. Any help would be much appreciated. Thank you in advance.

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Do you have another thermometer in the house?? What temp does it say? Either the t-stat is bad and showing the wrong temp or the hole in the wall behind the stat is to big, or there is something wrong with the outdoor unit and not cooling the house.