RPM's

[sebiches]

Hi i have a 4.6L 2k expedition and when i turn on my AC, the rpm's go up and down, but this seems to only happen when i'm on drive shift, if i put on neutral or parking it stays at normal rpm's. I was wondering what it could be, it does too sometimes even if the AC is not on, the rpms go up a little then down. for example there at 1k then goes down to 800 and so on. any advise?

 

[Black_Exhaust]

Do you notice the fan kicking in when the rpms drop or maybe a ratchet like noise or is it just odd fluctuations with no other noises?

 

[sebiches]

rpm

I dont think there's any other noises when this happens, but i'll pay more attention. and will let you know. what do you think it could be if that was the case? thanks for info.

 

[Black_Exhaust]

It could be the a/c clutch is slipping or that the strain of power steering, the a/c and possibly the fan could be bogging down the engine, heck with out those three things you could have an extra 20+ hp freed up, just to put in perspective what sort of a strain they put on the engine.

This is just a sort of educated guess, I'm not an expert by any means so I may be wrong, but this sort of a thing really shouldn't be an issue, maybe one or two tenths of a mile per gallon at low speeds but nothing more I'm sure.

Also these engines are equipped with something in the ecu or something that tells the engine to rev higher to heat up the engine faster, especially for those cold days where some heat is needed asap lol. so maybe that's just kind of messing with the things if your block is still cold or if you have an aftermarket thermometer. Hope this helps ya!