Intermittent cooling

[Rbs]

Need some guidance/opinions.  Have a Goodman 3ton condenser and coil. Temperature outside 80-85 degrees F.  Inside house temperature got to 78 degrees so turned on AC and set to 72 degrees.  Several hours later inside temperature leveled at 72.  Today, after'hold' 74 overnight, inside temperature has risen to 78 degrees with the unit running. Why will unit cool from 78 to 72 yet allows hold 74 to creep up even with the unit running?  TIA

[Admin]

What kind of thermostat do you have?

If you leave everything running does it eventually bring the temperature back down to 72F?

The fact you're able to reduce the temperature in a short period of time during a hot day would indicate there's no problem with the refrigerant charge.

Sometimes at this time of year when the nights get colder than 59F you can run into low pressure conditions that may cause a lockout, but the fact you say the AC continues to run has me scratching my head.

Are you sure the compressor is also running and not just the outdoor fan?

[Rbs]

Thermostat is older American Standard.  Don't know how to tell if compressor is running. The fan is certainly moving.  Cycled AC off for 1 hour.  Upon turning back on at an inside temperature of 78, it has now run for 2 hours and has dropped the temp to 74. Seems to operate correctly for now.  I'll try the 74 'hold' and see if the temp rises after running it on hold all night.  Water is pulsing out of coil and draining through the 'U' tube. Thx

[taiwanluthiers]

Need some guidance/opinions.  Have a Goodman 3ton condenser and coil. Temperature outside 80-85 degrees F.  Inside house temperature got to 78 degrees so turned on AC and set to 72 degrees.  Several hours later inside temperature leveled at 72.  Today, after'hold' 74 overnight, inside temperature has risen to 78 degrees with the unit running. Why will unit cool from 78 to 72 yet allows hold 74 to creep up even with the unit running?  TIA

I had the same problem with the mini split for my room. It would turn on, cool, but the cooling power seems to "level off" or decrease with longer run time and it was taking a VERY long time to cool it to temperature (we're talking hours to cool a small room from 28C down to about 25C). This is a 8000btu unit.

Then the compressor locked up and failed, and I replaced it just now. When the new compressor fired up and I charged it properly, it now cools the room from 28C down to 23C within 15 minutes.

You might have either a weak compressor or a low charge, or a broken metering device somewhere.

If you can measure your head pressure, and see what your compression ratio looks like... this can tell you a lot. My mini split didn't give me any way of knowing what the head pressure is, as it only has a charge port on the suction side. I believe it has a fixed orifice metering device. If I had to guess it was weak because shortly before the compressor locked up it was struggling to pump at a correct charge (compressor was VERY loud on startup and was very loud while running, with the suction pressure needle vibrating, indicating that the compressor was having issue maintaining the suction pressure as well).

I'd say try and see if there's an issue with the compressor, I'd be willing to bet if it wasn't a low charge or a severe overcharge, it's probably the compressor. Look into getting it replaced...

It might be expensive but the alternative is very high electricity charge AND hot days because it locked up in the middle of the night.

Unless you have a brand new inverter unit and the compressor just reduces its cooling power by slowing itself down, otherwise AC is either on or off, and the thermostat just tells it to turn on when it gets hot, and turn off when it reaches their set temp. Inverters are weird like that as in they can reduce their compressor performance in order to save energy.

Otherwise you're just wasting full amp draws for hours for no benefit if it is a fixed compressor and it's been running trying to maintain 74F