AC clutch engaging and disengaging RPMs oscillate

[sonsky]

94 base 4-cyl
When I turn AC on and rev up to 2000 rpms the ac clutch goes back and forth. During the normal driving the ac turns on for 6 sec, then is off for another 4 sec - so the cycle repeats every 10 secs. This has impact on rpms I feel a slight increase/decrease of power during the switching.
I suspect 2 problems that together make this effect:
1. faulty IAC valve that causes rpm drop when ac kicks on
2. leak or low pressure in ac system causing cluch to engage and disengage
But I may be wrong. I'm not a mechanic - just a user.

Any ideas?

[Ryan]

This happens in my mothers 04 Nissan Sentra as well. Manual tranny, no cruise. When the AC kicks in and out I can change speeds by up to 10km/h each way. Its really annoying, but I think its normal. Maybe not as extreme as you, but I think some change in the RPMs is normal with the AC coming on. Not as frequent either.

They say an AC is a load that uses up to 20hp. With a 112hp engine, thats a whole lot.
I prefer 2/60 AC

Mooneggs has the Eco switch and Shameen knows what it does. I think it fixes that problem?

[sonsky]

It turns out that the ac was overcharged and it was causing the clutch to engage and disengage. Adjusting pressure to the proper level fixed one problem.
I still have a question for u guys. Can someone check if the rpms drop on idle when u turn ac on?

[Volones]

Yes, your RPM will drop slightly when your A/C comes on, but then should raise to a slightly higher level and stabilize. As an example, my engine idles at 600rpm with no A/C, when the A/C kicks in, it will drop to about 300-400rpm, then raise to around 800-1000rpm and stabilize there, but it will feel much rougher (if that makes sense) than when it's idling w/o A/C.

The reason is exactly what Ryan mentioned, the A/C puts a load on the engine, so the ECU is forced to react to that load. It doesn't react immediately, nor can it predict when the A/C compressor is going to engage, so there is a drop in RPM until it compensates for the increased load, then it will idle higher since it's working harder. This is entirely normal for a small engine operating in a low torque area of its powerband, and nothing to be concerned about. I have considered getting a UD pulley, converting to manual steering, and even getting custom rods and cams to give my engine more torque at lower RPMs, but don't have the money or time right now to pursue either.

Anyway, good luck and I hope I didn't talk your ear off.
Vol!

[sonsky]

I understand that turning ac on should cause rpm drop but as you said - after that it should compensate and go back. Mine does not go back. Engine idles at 800rpm, when I turn ac on it drops to 400 and stays there.