I have a Gree Terra24HP230v mini split HVAC that's about six years old. Three months ago it would suddenly come on by itself (it was turned off by wireless remote, essentially in standby) and so I read the manual and found an override button ten feet up the wall where the unit is and pushed it. I didn't think this was a solution since it's only meant for a lost remote but it solved it for a month for no logical reason. The really problematic symptom is that it will suddenly go off and on twice a second as if I was pushing the button on the remote but then it might stay on for an hour. Yikes, no pattern here whatsoever.

This unit is out of warranty so instead of immediately calling the installer I removed the batteries from the remote to take that out of the equation but it didn't help and then I unplugged the display panel from the interior mainboard convinced it was a bad IR sensor and THAT didn't work. I also noticed a blinking red LED on the interior mainboard when up on the ladder and the cover is off where the 120v lines come in. I don't believe that's normal but there is no pattern to it, just constant beeping. There are also no error codes on the front panel.

I checked resistance on the ambient temp sensor and although I didn't get the connector off (these little buggers are not easily removed, I was afraid of ruining a pin or wire) I did read about 8k ohms which proves at least there's not a short although it could have been open and the reading was from another path on the board but since this is a sporadic symptom it can't be an open or shorted sensor, correct?

After much video watching and suffering the 95 degree heat I did eventually call the installer and he not only didn't show up but never called back after I sent a very nice text to let him know we could reschedule. I have forty years of general construction experience including electrical, have built two computers and do some simple electronics repairs so with your help I'm hoping to solve this myself. It may very well be above my pay grade to troubleshoot the mainboard if I can't get a new one but at least I'll have learned some things on the way.

The other telling symptoms that point to the interior mainboard is that now the up/down louver will start by itself when it's in cool mode (I've been able to get lucky and run it for an hour or two before it spazzes out) and also the display panel doesn't light up anymore although I can still use the remote. This has to be the interior mainboard doesn't it? Failing IC, mosfet, caps, dead bug?

If it helps I can slide out the mainboard and take a pic.

 

I had one of those remote control switch boxes that you plug in, then plug Christmas lights or a tree - or some other electrical thing. The remote was a single button key fob. I was setting it up to operate low voltage lighting. I wanted to know how far away I could be and still turn it on and off. As I was testing it over and over at differing distances my neighbor came to me carrying his wireless doorbell. Every time I pushed the button his doorbell would ring. Same frequency. Same code. I don't know which - but I'm wondering if something similar is going on in your area. Someone is operating some electronics that may be triggering your AC to switch on and off.

Another possibility is a bad ground, meaning there could be noise on the line and the circuitry is reading that noise as a command signal. It's going to be hard to tell from here what's going on there. But I'd recommend starting by unplugging it (or switching off the breaker) and checking for loose connections inside the unit. There could also be a bad solder joint whereby it is intermittently connecting and the change in signal may be triggering the ON - OFF cycle you're seeing.

I was watching TV (one of those older CRT TV's) when I noticed a dust bunny under the TV. It would leap up to the edge of the screen, hang out there for about 10 seconds, then drop off. Then 10 seconds later it would jump back up there again. Over and over, the cycle repeated. Took a while but I finally figured out that it was static electricity that was drawing the dust bunny up to the screen, then the intermittent degaussing ring would come on and eliminate the static charge.

Sometimes the strangest things have the simplest explanations.

 

I had one of those remote control switch boxes that you plug in, then plug Christmas lights or a tree - or some other electrical thing. The remote was a single button key fob. I was setting it up to operate low voltage lighting. I wanted to know how far away I could be and still turn it on and off. As I was testing it over and over at differing distances my neighbor came to me carrying his wireless doorbell. Every time I pushed the button his doorbell would ring. Same frequency. Same code. I don't know which - but I'm wondering if something similar is going on in your area. Someone is operating some electronics that may be triggering your AC to switch on and off.

Another possibility is a bad ground, meaning there could be noise on the line and the circuitry is reading that noise as a command signal. It's going to be hard to tell from here what's going on there. But I'd recommend starting by unplugging it (or switching off the breaker) and checking for loose connections inside the unit. There could also be a bad solder joint whereby it is intermittently connecting and the change in signal may be triggering the ON - OFF cycle you're seeing.

I was watching TV (one of those older CRT TV's) when I noticed a dust bunny under the TV. It would leap up to the edge of the screen, hang out there for about 10 seconds, then drop off. Then 10 seconds later it would jump back up there again. Over and over, the cycle repeated. Took a while but I finally figured out that it was static electricity that was drawing the dust bunny up to the screen, then the intermittent degaussing ring would come on and eliminate the static charge.

Sometimes the strangest things have the simplest explanations.

Thanks Tonyr1084, those are some good ideas and in a general sense what I was thinking or hoping even as an amateur electronics person although I'm wondering about the blinking red LED.

Many of the connectors on this board are so difficult to release I'm afraid of damaging pins or wiring so even if I had the skills to troubleshoot a component I may not even be able to safely remove the connectors. Their difficulty reminds me of many automotive connectors but at least those are larger and I can repair wiring, buy a new connector or even replace pins if I have to. It would be a three stooges event to remove and resolder anything up in the air like that with no way of securing the dangling MB.

Hopefully later today I'll check that out.

 

I removed the MB and did my best with a mag visor to look it over and I don't see anything obvious like bulging caps, broken solder joints etc. The main ground wire from the MB to the evap coil looks solid. The unit ran for four hours two days ago before I removed the MB and yesterday as well after I put it back together although I left out the display panel to see how things go without the IR in the circuit.

I forgot that the blinking red LED could have been SMP so when I had the board off I never noticed it but did again after installation and powering up the unit. I'll have to remove the board again and attempt to trace where it gets a signal from.

 

Here is a closeup of the blinking led indicated by the arrow. Is it a typical design to have an led blink when part of an IC goes bad? I also tried to take down the part number of the IC since the mainboard seems to be unavailable but I can't find it on any of the big semiconductor sites.

the numbers looks like
0211ZB10
C2BSSFNA

 

I found a new mainboard through the seller after my brother dug up the sales receipt from six years ago and that took care of the issue. Of course it took twelve days so I wasn't able to fix it for the hottest four days of the year but as I said before the unit sometimes would work for several hours and I got lucky during those days. It was as if the powering off at the panel would set the circuitry into a stable state sometimes if it had been left off for many hours.