Howdy,
Today I've been spending some time outdoor. The weather gets cold in here, we got around 15C or 60F. On my way back I've started motor to heat up the block and let it run for a minute or two. I've noticed, that under hood something goes "click... 5 seconds.... clack..... another 5 seconds" and over again.

I've raised the hood and found it's the AC clutch. It gets on and off. Inside the cabin I had a climate control set for 21C or 70F. I find it strange. I have an AC compressor replaced with UAC, that does not have the pressure switch built in, so I made the shunt on the plug (dunno if that matters). I've taken out the shunt to prevent any further clutch engaging.

Is that kind of behavior of AC clutch normal? Why the climate control unit wants to run the compressor, if the temperature inside the cabin is cooler than requested? Or maybe the temperature reading is fluctuating with a narrow hysteresis band? Any tips?

 

Are you by chance running it on defrost mode? Defrost kicks in the AC system to "dry" the air (pull the moisture out of the air) before it comes out of the defrost vents and hits the windshield, to prevent fogging up.

MAX AC selection will also make the AC compressor cycle even if you have the temp dial set to full heat, most likely (and I'm just assuming) for the same or similar reason.

 

Thanks! Good explanation, smart feature. Just checked - it was on defrost.