Engine misfiring when aircon is on

**Waterboy** · 2nd June 2009, 23:51

What with this sudden "summer", it's been the first time i've had the aircon on in the car since i bought it late last year.

Trouble is that when i have the aircon on, the car seems woefully slugish but more worryingly it seems to misfire and hesitate. Doesn't matter if i'm accelerating or have my foot off the pedal as i coast and slow down.

I know the power steering and aircon are al powered electrically (or are they? Is the aircon belt powered?)but surely even with the aircon on, there should still be enough power left to power a spark plug??????

As soon as the aircon is turned off, the car runs smooth again.

Any Ideas? Car is a 1.8 Club manual

**davidjameswest** · 3rd June 2009, 00:19

i had a similar problem on my mondeo st24 and never got to the bottom of the problem mate

**Waterboy** · 3rd June 2009, 12:59

Originally Posted by davidjameswest

i had a similar problem on my mondeo st24 and never got to the bottom of the problem mate

Damn, and i was hoping for a "A sensor connection has come off. Just plug it back in"

**Deztroyer** · 3rd June 2009, 13:03

is anything else electrical on ??

had similar issues on a ford focus 1.6
if heated screen and fans and headlights were on i couldnt open the drivers window
turn off the fans or heated screen and windows worked
underpowered alternator was the cause

**daveg360** · 3rd June 2009, 14:47

does the engine respond to the AC being switched on? it should pick up a little to compensate for the extra load at idle. Perhaps the ecu is not getting the input to do this.

**Waterboy** · 4th June 2009, 01:50

Yep, engine picks up when aircon is on.

Can't see any leaks, aircon is cold. No other electrical items on, not even the radio.

Aircon does squeel sometimes though. Was wondering if the belt driven motor was siezing or something so was causing the engine to go slightly out of sink as it may struggle to turn it.

Does that make any sense at all?