Hi,
When you hear the click, that indicated the compressor clutch is engaging the compressor. That is normal. Actually, the system cycles on and off, so you will hear it doing that.
As far as the RPMs, because of the engine size, you are likely going to see them drop a bit. Again, when the compress engages (clicks), there is a heavy load placed on the engine from the compressor. That's why you notice it.
Here is a link you may find of interest. It discusses how the A/C system works.
https://www.2carpros.com/articles/how-a-car-air-conditioner-works
Let me know if this helps or if you have other questions.
Take care,
Joe
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Monday, July 12th, 2021 AT 9:49 PM