Engine Rev Fluctuating With Aircon On

[Ockie]

Hello guys. Yes, it is another Ockie car question. Well, those that remember me. I am not sure who is who here anymore.

Anyway, now with the temps rising into the high 20's in JHB, I have every now and again put the aircon the last few days. I noticed two days ago that with the aircon on, and the car is in neutral and idling while at a red robot for example, the rev counter will dip from 1 to 0.5 and then rev back up to 1. I am not exactly sure if this is a new thing because it has been winter so have not used the aircon for quite a while. Car had its 35 000Km service from Hyundai last week. I did not bring it up because I was not aware of it.

I do remember many many many years ago in my 20's when I drove a VW Polo it did the same when the aircon was on. But that was a second hand car with a 3rd party aircon installed when the company bought the car from the dealership.

Should I be worried? This service the car was in for now was the last on the service plan, but the car is still very much under the Hyundai warranty.

It is a Hyundai Atos 1.1 Motion 2022 model.

 

[Sinbad]

It's probably ok. As the compressor kicks in (remember it works in cycles) it takes power from the engine which drops the RPM, and it takes a second or so to compensate and bring the idle speed back up to where it should be.

 

[Ockie]

It's probably ok. As the compressor kicks in (remember it works in cycles) it takes power from the engine which drops the RPM, and it takes a second or so to compensate and bring the idle speed back up to where it should be.

OK, thanks meneer. Not going to stress about then meneer.

 

[Pax]

Normal for small engines

 

[Robocop]

I fit happens often (like every minute or 2) it can indicate low gas in the compressor.

 

[ArmatageShanks]

Yeah thats normal, my bantam does this when you turn anything on with high current draw, because the idle control is lazy ans and the alternator probably schite.

 

[Gordon_R]

I would be more concerned if the rpm's drop while driving, since that is a safety issue! The ECM should add power to keep the rpm's constant, but there may be a faulty setting (or delay).

On my (old) Camry automatic the rpm's actually increase at idle when the aircon is turned on. Uses more fuel, but definitely avoids a loss of power when needed.

Edit: You may be experiencing the opposite problem as the compressor cycles off and the rpm's drop. IMO an idle speed of 1000rpm is too fast and 500rpm is too slow, but it is a small engine...

 

[airborne]

It's probably ok. As the compressor kicks in (remember it works in cycles) it takes power from the engine which drops the RPM, and it takes a second or so to compensate and bring the idle speed back up to where it should be.

Normal for small engines

Fluctuating to that degree isn't normal and any modern small engined car can handle an aircon no problem, the engine should barely notice it other than slightly labouring as it cycles on an off, never dropping to 500rpm from 1000rpm.
It can perhaps happen if the battery is on the way out and the full current draw is being pulled from the alternator and the engine is struggling to cope with the load from the alternator and aircon pump at the same time.

@Ockie welcome back, considering it’s so new is the vehicle still under warranty?

 

[Neuk_]

Fluctuating to that degree isn't normal and any modern small engined car can handle an aircon no problem, the engine should barely notice it other than slightly labouring as it cycles on an off, never dropping to 500rpm from 1000rpm.
It can perhaps happen if the battery is on the way out and the full current draw is being pulled from the alternator and the engine is struggling to cope with the load from the alternator and aircon pump at the same time.

@Ockie welcome back, considering it’s so new is the vehicle still under warranty?

Current draw for what exactly? Unless these modern small engine cars use electrical driven aircon compressors...

 

[Gordon_R]

Current draw for what exactly? Unless these modern small engine cars use electrical driven aircon compressors...

Some cars do use electrically driven compressors. Everything is about fuel economy nowadays. Massive draw on the alternator is a possible reason for the fluctuations.

Edit: Mostly used on EV's and hybrids, unlikely on econoboxes and 12V batteries.

 

[Ockie]

Fluctuating to that degree isn't normal and any modern small engined car can handle an aircon no problem, the engine should barely notice it other than slightly labouring as it cycles on an off, never dropping to 500rpm from 1000rpm.
It can perhaps happen if the battery is on the way out and the full current draw is being pulled from the alternator and the engine is struggling to cope with the load from the alternator and aircon pump at the same time.

@Ockie welcome back, considering it’s so new is the vehicle still under warranty?

Thank you.

Yes, it is still under warranty. It is just the service plan that is now finished after last weeks service.

 

[SHL]

Hello guys. Yes, it is another Ockie car question. Well, those that remember me. I am not sure who is who here anymore.

Anyway, now with the temps rising into the high 20's in JHB, I have every now and again put the aircon the last few days. I noticed two days ago that with the aircon on, and the car is in neutral and idling while at a red robot for example, the rev counter will dip from 1 to 0.5 and then rev back up to 1. I am not exactly sure if this is a new thing because it has been winter so have not used the aircon for quite a while. Car had its 35 000Km service from Hyundai last week. I did not bring it up because I was not aware of it.

I do remember many many many years ago in my 20's when I drove a VW Polo it did the same when the aircon was on. But that was a second hand car with a 3rd party aircon installed when the company bought the car from the dealership.

Should I be worried? This service the car was in for now was the last on the service plan, but the car is still very much under the Hyundai warranty.

It is a Hyundai Atos 1.1 Motion 2022 model.

Do you notice any power lag or stutter, especially when accelerating from standstill?

 

[Ockie]

Do you notice any power lag or stutter, especially when accelerating from standstill?

No. I can feel the car has a bit less power, which is normal. No stuttering or lag though.

 

[airborne]

Current draw for what exactly? Unless these modern small engine cars use electrical driven aircon compressors...

If the battery is faulty the alternator has to work overtime trying to charge the battery and feed the entire electrical system, that puts a greater load on the engine and may make it struggle in conjunction with the aircon. Modern vehicles have lots of electrical bits and bobs, many have electric steering racks etc. Just one aspect, it could also be a throttle body issue or sensor issue that makes the ecu struggle to maintain consistent revs at idle.

Thank you.

Yes, it is still under warranty. It is just the service plan that is now finished after last weeks service.

I’d take it back to the dealer then, see what they say and if then post back here what they say before they go ahead and do anything. Dealers are sharks..

 

[NR7]

Hello guys. Yes, it is another Ockie car question. Well, those that remember me. I am not sure who is who here anymore.

Anyway, now with the temps rising into the high 20's in JHB, I have every now and again put the aircon the last few days. I noticed two days ago that with the aircon on, and the car is in neutral and idling while at a red robot for example, the rev counter will dip from 1 to 0.5 and then rev back up to 1. I am not exactly sure if this is a new thing because it has been winter so have not used the aircon for quite a while. Car had its 35 000Km service from Hyundai last week. I did not bring it up because I was not aware of it.

I do remember many many many years ago in my 20's when I drove a VW Polo it did the same when the aircon was on. But that was a second hand car with a 3rd party aircon installed when the company bought the car from the dealership.

Should I be worried? This service the car was in for now was the last on the service plan, but the car is still very much under the Hyundai warranty.

It is a Hyundai Atos 1.1 Motion 2022 model.

It's a 50kw naturally aspirated engine that loses up to 18% of its power at Jhb altitude and is then being asked to power the AC compressor, it sounds fine to me.

 

[Neuk_]

If the battery is faulty the alternator has to work overtime trying to charge the battery and feed the entire electrical system, that puts a greater load on the engine and may make it struggle in conjunction with the aircon. Modern vehicles have lots of electrical bits and bobs, many have electric steering racks etc. Just one aspect, it could also be a throttle body issue or sensor issue that makes the ecu struggle to maintain consistent revs at idle.

Yes, but traditionally all aircon compressor pumps are mechanically driven, not electrically so it being on shouldn't have any affect on the alternator. This obviously isn't true if the aircon compressor pump is electrically driven but I don't know how many modern cars use electrically driven aircon compressor pumps, I have only seen retro fit kits like VWSA did for some CitiGolf's. I don't recall @Ockie saying that his car's rpm dips all the time, only when the aircon was on...

 

[SauRoNZA]

Aircon eats about 6kW on startup and then settles down which is why you see the revs dip.

Quite normal for small engine cars like these.

Every small engined N/A car I’ve ever driven has done exactly this. Opel Corsa’s, Chevy Sparks, Toyota Corollas, Picanto’s, Half tonne bakkies etc etc.

Why we called the Aircon button the Turbo button as young lads because it gave you more power when you turned it off.

 

[Ockie]

I don't recall @Ockie saying that his car's rpm dips all the time, only when the aircon was on...

Yes, it only does this when the aircon is on and I am in neutral at a red robot.

 

[Ockie]

Why we called the Aircon button the Turbo button as young lads because it gave you more power when you turned it off.

Yes, my mom always did that when we were driving somewhere on the open road going to visit her parents. When she wanted to overtake she would turn aircon off and then go for it. lol That was still in a Nissan Sentra I think it was called. Aircon was a must though, we were living in Springbok in Namaqualand.....35 - 40 degrees outside easy.

 

[RedViking]

and the car is in neutral and idling while at a red robot for example, the rev counter will dip from 1 to 0.5 and then rev back up to 1

Mine does it on my Hyundai Accent 1.6 2006 model for a little bit when the aircon kicks in. But car adjust accordingly. It's not that bad though and revs don't dip that low.