A/C causing engine lag

[TiptreeFord]

My 2009 Fiesta had its aircon refilled the other weekend, but since I've noticed that the engine lags when the a/c is turned on, and has rather sluggish acceleration. It's already only a 1.4 petrol, so performance is already limited - it really struggles when the a/c is on.

Is this normal, or indicative of an issue with the compressor?

[niknakmb]

Somebody once told me that you lose about 10 bhp from the engine when the compressor cuts in, maybe it just wasn’t working until the regas?

[pragmatix]

50 minutes ago, niknakmb said:

Somebody once told me that you lose about 10 bhp from the engine when the compressor cuts in, maybe it just wasn’t working until the regas?

Depending on the car its 2-3 bhp, so in answer to the op, there is somthing else wrong with your car, it may well be related but it i cant think how.

[TomsFocus]

It's a lot more than 2-3bhp for the AC compressor.  Very noticeable with a small engine, much less so with a larger one.  However the AC should cut if you want max acceleration, so try giving it full throttle and see what happens, if it's still very laggy there's likely to be another issue.

[pragmatix]

9 minutes ago, TomsFocus said:

It's a lot more than 2-3bhp for the AC compressor.  Very noticeable with a small engine, much less so with a larger one.  However the AC should cut if you want max acceleration, so try giving it full throttle and see what happens, if it's still very laggy there's likely to be another issue.

Once running the bhp is a lot less than the initial start up, I had a 1.2 fiesta with a/c and cant say i noticed a drop in performance

[TomsFocus]

2 minutes ago, pragmatix said:

Once running the bhp is a lot less than the initial start up, I had a 1.2 fiesta with a/c and cant say i noticed a drop in performance

We'll have to agree to disagree on that.   I've had various cars and have noticed a drop in midrange performance with the AC on in most of them, even including the 140bhp 1.6TDCi Focus.  The 1.0VVTi in the 107/Aygo is horrendous with the AC on, actually had to turn it off for certain hills!  

[pragmatix]

10 minutes ago, TomsFocus said:

  The 1.0VVTi in the 107/Aygo is horrendous with the AC on, actually had to turn it off for certain hills!  

Ill give you that, my friend has one, infact you could have just said horrendous car😂

[TiptreeFord]

35 minutes ago, TomsFocus said:

It's a lot more than 2-3bhp for the AC compressor.  Very noticeable with a small engine, much less so with a larger one.  However the AC should cut if you want max acceleration, so try giving it full throttle and see what happens, if it's still very laggy there's likely to be another issue.

There's definitely a noticeable lack of power once the compressor kicks in. I haven't noticed any difference whether I'm full-throttling or not, but I'll give it another go later and see what happens.

[TomsFocus]

8 minutes ago, pragmatix said:

Ill give you that, my friend has one, infact you could have just said horrendous car😂

Yeah, mine lasted all of about a week before I returned it to the dealer and bought a Focus instead!   My sister has one though and it suits her fine, just a bit slow in some places (going on holiday fully loaded is the biggest issue lol) but I must admit it's been 100% reliable...just serviced once in 4 years and no engine problems at all!!

[Bobr]

I use A/C quite a bit in this weather and have never noticed any difference.

[David73]

On 7/13/2018 at 11:31 AM, pragmatix said:

Depending on the car its 2-3 bhp, so in answer to the op, there is somthing else wrong with your car, it may well be related but it i cant think how.

Idle fuel consumption on mine rises by between 0.1-0.2 gall/hour depending on weather. 0.1 gall/hour is 3kW, which, after engine efficiency considerations, roughly matches your figure for mechanical power. However, the 1.4 engine is only capable of generating about 30hp at 2000rpm so 2-3hp so is a more significant low speed load than to an Ecoboost.

Mine is an auto gearbox so combine the AC on/off action to gear changes as the pedal is moved, the car can lurch horribly when trying to make a brisk but not all out start.