Is it normal for my mini-split to keep cycling on and off?

A 12,000 BTU unit in a single guest room is almost certainly oversized, wich explains why you're seeing that start-stop behavior instead of a steady hum. Most guest rooms only need 6,000 to 9,000 BTUs at most. When the capacity is too high, the system hits the target temperture so fast that the inverter can't modulate down low enugh to stay running. It basially turns into a standard on/off window unit because it has nowhere lower to go. The first thing you should do is **lock the fan speed** to a medium or low setting rather than using 'Auto.' Many people don't realize that in Auto mode, the logic often prioritizes reaching the setpoint quickly, which triggers a blast of air followed by a total shutdown. By fixing the fan speed, you force the indoor coil to maintain a more consistent temperature, which can help the compressor find a lower 'floor' to cruise at. If you really want to verify what's happening, get a cheap plug-in power meter. A system that is 'dialed in' will show a steady, low wattage draw for hours at a time. If you see the power usage spiking to 800 watts and then dropping to zero every fifteen minutes, that's **short cycling**. It’s bad for the hardware and it’s terrible for dehumidification because the coil never stays cold long enough to actually pull moisture out of the air. Check the behavior on a mild day when it's only 70 or 75 degrees out. A properly sized and modulating unit should be able to run at a whisper for thirty minutes or more without clicking off. If it's still blasting and quitting during light loads, your installer likely oversized the head for that specific square footage. You might be able to mitigate it by leaving the guest room door open to increase the 'load' on the unit, giving it more air to process so it doesn't satisfy the thermostat quite so fast.

I dealt with this on my shop unit. The sensor on the wall unit is ussually trash becasue it’s sitting right in a pocket of its own cold air. I switched my remote to "Follow Me" mode and moved it across the room. That alone stopped the constant start-stop because the unit finally had an accurate read on the actual living space temprature.

If your remote doesn't have that, try pulling the front cover and making sure the little copper thermistor isn't touching the cooling fins. I had to gently bend mine out about half an inch so it stopped getting false "cold" readings from the metal. Total game changer for getting it to acutally modulate.

Reminds me of the old central units we used to slap in back in the 80s—if you oversized the tonnage, you’d rot the floorboards out from the humidity because it never ran long enugh to drain the condensate pan. These fancy inverters are supposed to be smarter, but physics is physics. If that unit is short-cycling, your humidity is probably hovering around 60% or higher. Stick a hygrometer in there and watch it. If the temp is 70 but it feels like a swamp, your unit is just a glorified fan. I’d bet my last dollar the installer didn't even do a Manual J calc.

Check your minimum modulation floor. If that's a Mitsubishi GL12 or similar, the compressor can only drop down to about 1,700 BTU. In a small guest room, even that 'low' is too much heat removal, so it's going to cycle. It's the curse of the 12k heads—they just don't have the turndown ratio of a 6k or 9k unit. If your installer didn't check the Delta T across the coil once it's 'steady,' he missed the boat. Grab an infrared thermometer and hit the supply air; if you're seeing 40F air and then it's dead silent two minutes later, that inverter is just hitting its hard limit and giving up.

While the previous points regarding the modulation floor and remote sensor placement are certainly valid, I whould highly recommed you meticulously examine the return air thermistor’s positioning relative to the coil's proximity; if the plastic casing is slightly misaligned, the sensor often gets 'ghosted' by residual thermal mass from the evaporator assembly itself. Furthermore, you should verify if your installer performed a proper evacuation down to 500 microns with a calibrated micron gauge, as non-condensables in the line set can artificially inflate head pressures and cause the inverter board’s logic to prematurely truncate the cooling cycle before the thermal load is actually satisfied.