A/C off but clutch engages

Hi, thank you for the quick response, you guys are really helpful.

No codes recorded for anything and AC is showing as N/A.
No humidity sensor but there is an external temperature sensor mounted in the front fender and a thermistor in the cab heater unit. There is a coolant temperature sensor on the AC compressor and just a pressure sensor on the AC high side pipe. I have some info for a very similar variant of the car.
The coolant level in the radiator has never required topping up and appears normal and I have not noticed any antifreeze odor in the cab so I don't think the heater matrix is leaking.
However, as part of these checks I have noticed that I have an engine coolant thermostat that appears reluctant to open. The radiator bottom hose is cold for too long. Should start opening at 82 C but looks like at least 90 C measuring temperature at / adjacent of the thermostat housing. The dash overheat warning light (no gauge just blue and red indicator lights) only comes on when I first start the engine, presumably as a check. The cabin heater churns out hot air when required but this is not so good as it was at middle setting (maybe my memory playing tricks) (I've never had the need to have the heating set to full). This indicates to me the water pump is working okay, pushing coolant through 3/4" heater pipe and not thermosiphoning, but the temperature may be reduced a little by the AC compressor cycling and dumping cold into the heater unit even though AC is turned off. Presumably an internal baffle in the heater unit would prevent most of the cold air mixing with cab air - that does raise a question, what happens to any water that condenses on the evaporator under this circumstance, could this be the source of moisture?

My priority is to change the thermostat this weekend. That should make it easier to see the wood for the trees. Would higher than normal coolant and therefore engine temperature cause cycling of the AC compressor, even with the AC turned off?

Many thanks for your time and patience.

Installed a new thermostat this morning. The AC compressor clutch no longer cycles, engaging and disengaging, when the AC switch is off.
However, when the AC is switched on the cycling restarts, at least at idle, not noticeable when driving.

I only have a low DIY filling kit with low pressure gauge so did the best of a bad situation and connected it up. Low side, at 12C (54F) with the AC on 20/25 Psi, and then when the clutch disengaged it went up to 40/45 Psi. This seems normal? I should add I have never recharged the AC on this car.

When test driving with the AC off, the heater seems noticeably cooler, unless turned full on when it is really toasty. The old thermostat was reluctant to open early so maybe a bit of over-temperature.

Got some technical info for the car off the web which seems to support what you say. It states:
- “Compressor Energy Conservation Control. Optimum ON/OFF control of the compressor is achieved according to the outside/inside air mode air temperature (air temperature sensor), and insulation.”
Also
- “Detection Control For Refrigerant Leaks. When it is judged from the air temperature (air temperature sensor) and the refrigerant pressure (A/C pressure sensor) that the refrigerant amount is the specified value or less, or the refrigerant pressure is abnormal, the compressor is forced to be cut off to protect the A/C system.”

What next please?