AC on causes RPMs to fluctuate

[TestMe]

While driving down the road with the AC on my car does fine. But when coming to a stop and braking the RPMs rev up and down. But when I get to a complete stop it idles just fine. Any suggestions on what might be causing this????

 

[mustangmike6996]

this is normal. Engines will fluctuate a few hundred RPM for a few reasons, mainly Alternators kicking on to charge batteries (normally after a cold start) and AC compressors cycling to circulate the refrigerant in the lines. AC compressors also are active when using front defrost, the evaporators help dehumidify the cabin air reducing window fogging. On newer cars with drive-by-wire systems there are more things that can cause RPMs to change. That is all embedded in the tune or factory programming.