With a split unit aircon unit the compressor and fan would keep running even when the unit inside was turned off.

I figured out it was probably the relay sticking, so I replaced it on the control board inside the unit inside and it seems to work fine now. The other relays on the board were for different fan speeds.

However I'm having some second thoughts, is it probable that the outside compressor/fan unit has it's own relay that could be sticking? from what I could look from this units design I think the 220v AC power going to the outside unit is routed through the inside unit and the 220v flows to the relay at all times so the relay I changed would have caused the compressor to be on all the time if it stuck in the closed position.

1 Answer 1


If a repair fixes a problem, then in general one does not look for more things to do. Wait before you do anything more.

In my experience the 240 V power line goes directly to the condensing unit outside. In the US there is usually no 240 V line to the air handler inside. In the US most residential air handlers use 120 V on an entirely different circuit from the 240 V line to the condensing unit outside.

There is a "relay" (called the contactor unit) inside the condensing unit which switches off and on the 240 V high current power to the compressor and fan. Failure of the contactor unit is common, but at present you have not given any reason to suspect yours should be replaced.


But in Europe there is only one voltage 230 V to 240 V so the air handler would be at 240 V. I assume that the air handler and the condensing unit would still be on different circuits, but I really don't know.

  • 1
    A relay fixed it was enough for me. agree mostly, some split units do have line voltage but with no brand or model we could not say either way.+
    – Ed Beal
    Sep 9, 2019 at 13:20
  • This is in Thailand(230-240v). the outside unit isn't as easily accessible. I'm not even sure of the brand. Sep 11, 2019 at 6:27
  • Is this one of the so called mini-split ductless units? Sep 11, 2019 at 8:15
  • 1
    I believe it's a proper "split" type unit. the compressor with it's radiator are outside in it's own box and the lines run there through the wall and the cooling unit is inside(when the compressor ran full time even with the unit turned off all of those got ice on them too and the unit inside as well on the heat exchanger). It's been working all right for whats it worth. Sep 12, 2019 at 8:07

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