A/C compressor cycles on and off while driving?

The mechanic from Prilep (the city where I left the car on Saturday) has just called me and told me that the system is filled up, also he returned back the old high-pressure switch.
He gave me explanation that short cycling while driving is due to extremely cold state of the evaporator, and it has mercury thermostat to prevent getting frosted (I honestly don't believe in this too much).

I took the car yesterday, it worked fine 50km way to home.

It was daytime and a lot of traffic, I am not 100% sure. Tonight, I drove in very calm conditions because there is almost zero traffic at night, and the cycling is the same, about 10 seconds when driving, when stop it is continuously running on idle. So, my logic is that it cannot be true that "evaporator is freezing so that's why compressor shuts off" because if it freezes, it will also freeze on idle. I have no more idea what to inspect anymore.

Any advice on what step can I make on my own? I have no more where to take the car. :(

This period I didn't drive the car, but tonight I will make the same inspection again.

Outside temperature was 16°C (if that matters something). My small dash bulb is wired to the power source of R3 that is a clutch power relay. It is normally closed, so when energized it opens the contact.

Ignition on and bulb lights, push A/C button and bulb shuts off, the compressor runs.

Tested on both options (temperature set to hot - 25°C and temperature set to Lo), when stay in place on idle, the bulb stays off and clutch is energized all the time, start drive, it cycles on every 9-10 seconds.
Also made a test in place on idle, pressing the gas pedal, clutch shuts off after 2-3sec.
Ran the car in free motion (idle) on down warded street, clutch stay on.
Ran again on down warded street in gear (2-3) without gas, clutch still on. Pressing gas, start cycling.

In a moment of time, I got some conclusion on my mind maybe there is some reason in WOT circuit, but as I can search, there is no WOT relay on diagrams (thought it could be the same relay with both functions but different sources of control).

In the attachment there is a diagram picture of the power distribution box.

Please stay with me just a little more time in these hard moments for me, I don't have anyone to consult. It is not about the perfection of this scrap of a car, but about solving something so simple that it looks like a big mystery to our electricians and mechanics.

Thanks in advance and best regards from North Macedonia!

No, I have not, because I could not find the same here because it is normally closed and most of relays are normally opened. (Additional question: if it is the relay, how could it work all time on idle? Also, I opened it to see the contacts they were perfect.)

Tonight, I made another try, disconnected throttle position sensor, and drove the car for couple of kilometers but the problem was the same.

I know that I am annoying, also it is hard for you to make theoretical conclusions or predictions when you don't have the vehicle in front of you and also I don't have advanced equipment to be able both work on distance, but I must tell you every testing and results, because it is the only way that may lead to the root of problem.

Today I made a day test, drove about 15km through the city (outside temperature was 27°C if it matters) the A/C temperature was set to 19 then after a while to Low, and the bulb didn't light even once (the compressor was running all the time without cycling.

Thanks once more for your steel nerves and patience, I would be happy for your next advice?

As I told you, I don't have advanced tools and cannot measure pressures, also as I told you, compressor makes short cycling at night, because today when it was sunny it was on all the time as I explained in previous reply, and also as I told you in previous replies it shuts off when the relay stop receiving power.

Also, as I mentioned before, the temperatures outside were 16 and today 27°C, if that leads somewhere to the root.

As I explained, night driving, outside 16, AC set to 25, stay in place, compressor run continuously and vents blow warm air, press gas pedal, compressor starts cycling on and off every 9-10 seconds (relay that controls the clutch receives and loses the power). Start driving, compressor short cycles again. Driving in idle on down warded street, compressor stays on. Driving in shift but without gas, on down warded street, compressor still stays on, pressing gas, it starts cycling.
Made same tests on AC set to LO, everything the same.

Today, outside 27, drived 15 km through the city, compressor stayed on all the time and cold air blowing as it should.

Could it be some fault of ambient temperature sensor? Yesterday I drove 80km, outside was 27°c, compressor didn't shut down even once. This morning when coming back from work, turned on 22°c to demist the windshield, outside was 13°c, short cycling was the same.