I’m suspecting an upcoming issue with my split AC system. Currently it is working and cooling, however in the last week or so, I’ve noticed that after the AC reaches the set temp, the copper line inside at the air handler sounds like refrigerant is flowing. The line is hot to the touch, not burn you hot, but hot.

Leaving for work one morning I then noticed the condenser unit fan shut off as the AC reaches the set temp, but a humming (compressor?) with the fan off. The whole CU is again, hot to the touch. This will on for about 10 minutes or so after the CU fan and AH shut off. Happens in the heat of the day and at night. More often than not, but not all the time.

Compressor is new. Goodman system. CU coils aren’t dirty. AH coils aren’t too bad either.

“Flowing” noise goes away when AC is running.

System is in South Florida.

Any ideas of why this would happen?

  • Do you expect the line set to cool the instant the system shuts off? It takes time to dissipate the heat in the pipes...
    – FreeMan
    Commented Jan 1, 2021 at 18:30
  • I understand that. But: 1) the exposed copper line at the air handler is not always hot, not hot when the unit is running and not hot when the AC shuts off normally. 2) I am working outside right now and the CU shut off completely when the AC reached the set temp. As I mentioned this happens when what sounds like the compressor stays running after the fan on the CU shuts off. Commented Jan 1, 2021 at 18:36

1 Answer 1


If in Cooling mode neither line should be “hot” but warm is fine. If you are in heating mode hot is ok I know you said cooling but make sure your thermostat is in cooling as a large temp swing can cause it to change modes in auto.

A low refrigerant or “Freon” charge can also cause problems as there is not enough gas to be compressed to a liquid and get cooled properly. If recharged prior to drawing air into the system it may not be horribly expensive, but a pound of R22 costs $100+ these days other types are usually half that cost per pound.

The noise after the compressor stops is normal as the system pressures equalize this can last in excess of 5 minutes depending on type of control.

You said a new compressor so it should have had a new capacitor installed and without knowing the control method running for a short time after the set point is reached this may be ok.

Since hvac servicing requires a license other than cleaning coils there is not much we could do and having a service call could save quite a bit if done now prior to s failure.

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