RPM fluctuation when A/C is on

[Caretaker]

For the past year, my '09 has had a glitch when the A/C is on. While driving, especially under 40 miles per hour, the RPMs will dance between 1500 and 1900 when the A/C is on. This does not happen when the A/C is off. The sensation is almost like the transmission is searching for a gear. I had the MAF sensor sprayed and cleaned, but that has not resolved the problem. The PCV has never been changed, nor the plugs. Any thoughts?

[Chiadog]

Sounds like the AC compressor is cycling on-off-on-off. Have you tried to repeat this situation in PARK or NEUTRAL holding a constant gas pedal at 2,000 rpm, with an accomplice er, helper watching the AC compressor for cycling with the hood open?

[kumquat]

I'm actually going to suspect a low refrigerant charge. The compressor will cycle off when it detects insufficient pressure on the LP side. When the compressor goes off, the LP pressure will go up as the LP and HP sides equalize. Once it's high enough the compressor will switch back on.

So the first thing I'd do after looking at the compressor with the car running to confirm it's actually cycling on and off that rapidly would be to check the pressure on the low side while it's running.

[Caretaker]

Thanks to both of you. I shall investigate into what you have provided.