[kloker]

It is not normal. If you left it on, it should still be on. However, this is not a good idea. You should always shut down your A/C whenever you park the car. Leaving it on allows the compressor to be left under pressure, which, over time, can lower the service life of any and all seals in the A/C system, but especially in the compressor, as well as causing leaks over time. leading to loss of refrigerant.

 

[kloker]

The pressure doesn't go away when the compressor isn't running, it just equalizes between the two side of the system. I don't think that the system knows the difference between the compressor not running because the engine is stopped or the compressor not running because it's declutched. Could be wrong, my says I frequently am.

https://gobdp.com/blog/what-should-my-ac-pressure-be/

From the above webpage:

"Thanks for your question about your Nissan Sentra. When your AC compressor isn’t running, the pressure in your system equalizes between the high and low side. What that pressure should be depends on the design of your system and the temperature outside when you take the measurement, but 100 psi with the compressor off may be just fine. When the compressor turns on it should lower the pressure on the low side of your system and that pressure again is dependant on ambient temperature and other factors. If the pressure isn’t lowering in your system with the AC switched on, then either your compressor isn’t running, or it has an internal failure.
Thanks again for your question!
-BD Auto Pro"

And this Toyota dealer has this about it.

https://www.toyotavacaville.com/blog/should-you-turn-your-a-c-off-before-turning-off-your-car/

From Top Gear, the explanation for turning it off has to do with electrical load when starting which once upon time made sense when starting a car was a bit of adventure as opposed to today's starts where the engine hardly spins before it fires.. But these days, I wonder if the cars aren't smart enough to disable the air conditioning system during cranking?

https://www.topgear.com.ph/columns/...c-before-i-switch-off-the-engine-a20-20160301

My point is that when you shut the engine off leaving the A/C on, the compressor is left under high pressure. Yes, the pressure, over time, equalizes, meaning that after that the high pressure condition goes away. If instead you shut it off first and let it cycle off before killing the engine, it equalizes then, thereby releasing the high pressure condition that is undesirable when the compressor is not turning, which relieves stress on the seals. The better care you take of those seals, the longer they will last. Any real A/C tech can verify this. The years may have made some small advancements in how these systems function, but in this regard they are no different now than they have ever been. The high-to-low side differential is still there, still has the same internal function, and still affects the seals in the same way. And those seals are all-important in the life of the system. It's just common sense. The relation to electrical function is a completely different issue, and one I didn't comment on.