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During hot days when the air conditioner is on a lot it comes to a point in the evening when the air conditioner shuts down and the fan (from furnace) stays on. This will go on all night as the house gets hotter. Thermostat will be set at 72 and the temperature in the house will be 75. If I turn the thermostat up to 76 the fan will go off. If I wait a while and turn it back down past the temperature of the house the air conditioner will kick back on for a while. Shouldn’t the air conditioner stay on until the house temperature gets to the temperature off the thermostat

  • Is the air conditioner overheating? The condenser (outside bit) might have a motor or such that overheats, shutting the air conditioner off until it can cool down. – IronEagle Jul 6 '18 at 14:13
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    Is your thermostat programmed to do this, based on time of day? – Phil Freedenberg Jul 6 '18 at 14:41
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    Could be refrigerant charge needs checking. – Jim Stewart Jul 6 '18 at 15:09
  • The fan is from the air handler which can run when the compressor doesn't. It is the compressor that provides the cooling. The air handler (fan) just moves the air. You could have a failing capacitor, be low on refrigerant, or sometimes have a bad fan motor on the compressor unit and the compressor shuts down when it gets overheated. – Bill Jul 10 '18 at 22:18
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There are a lot of possible reasons this could be happening, but here are some common ones:

1. Frozen coils

If too much moisture remains inside the indoor unit, it can freeze and form big blocks of ice around the refrigerant coils. Instead of cooling the air, the refrigerant just keeps making more ice.

There are several common reasons for icing, especially if the unit has been running for a long period of time:

1a. Icing due to clogged drain

If the condensate drain out of the unit is clogged, the backed up water causes elevated moisture levels in the air inside the unit which form ice on the coil. As more water sitting in the drain pan evaporates, the ice gets thicker.

Find the condensate drain from the indoor unit and check it. How to do this will vary depending on your unit.

1b. Icing due to poor airflow

This is most commonly seen on units with very dirty air filters. The airflow through the filter is restricted, meaning that not enough air is flowing through the coils. As above, the moisture condensed on the coils freezes. It can also happen if the return vents are blocked by items in the house.

2. Failing capacitor

Inside the outdoor unit of your air conditioner, there is a large capacitor that is used for starting the unit. If this capacitor fails, the outdoor unit won't run and the refrigerant won't circulate. Make sure the thermostat is calling for AC (turn it really low) and go outside and see if the fan and compressor are running. If they are not, listen closely to see if you hear a faint humming noise. If you hear the hum, you need a capacitor.

3. Low refrigerant

You probably need to get an HVAC professional to check this one - they have special tools to measure the refrigerant flow through the system.

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