Does A/C actually affect engine performance?

[DropTopDon]

I've always thought that having the A/C on worsens performance very slightly and decreases MPG's. On my old TJ I could definitely feel the difference in driving with the A/C on and off. In my LJ though it feels relatively the same with the A/C on but I haven't tracked MPG's. So is it true that A/C affects fuel economy or performance or is it just placebo effect?

 

[srimes]

I've always thought that having the A/C on worsens performance very slightly and decreases MPG's. On my old TJ I could definitely feel the difference in driving with the A/C on and off. In my LJ though it feels relatively the same with the A/C on but I haven't tracked MPG's. So is it true that A/C affects fuel economy or performance or is it just placebo effect?

It's true. A/C takes energy to run, and that energy come from the engine. There's no free lunch.

This applies to most EVERYTHING in the car: headlights, blower motor, radio, etc. They may be too small to really notice but if it takes electricity it takes gas. One exception is heat as that's captured from otherwise wasted energy.

 

[Wildman]

I don't remember how long ago this was but one of the car mag's did a write-up on running with A/C or windows down for cooling and they found that you used less fuel then running with your A/C on and windows rolled up. Now as srimes said there is no free lunch and it takes HP to turn the A/C compressor.

 

[SSTJ]

As others have said, it’s true.

In my 2.5, I sometimes switch off the AC for a minute in order to avoid downshifting up hill in traffic.

 

[BlueC]

Yes, A/C takes power to run, as does every other engine driven accessory. Engine Masters covered this with what takes how much power (engine driven cooling fan w/ clutch is like 7-10 hp). I think Myth Busters covered the topic of A/C and MPG and showed that below 45 mph, A/C off and windows down was better for MPG, above 45 windows up and A/C on.

 

[freedom_in_4low]

I don't seem to feel it as much with torquier engines but I've definitely had 4 cylinder cars where I could feel the compressor cycling. I once narrowly avoided plunging an MX5 into the Arkansas river once after the cycling of the compressor (which was running due to using the defroster) made enough change in the engine output to break the tiny shred of traction I was tenuously holding onto as I descended an icy hill toward a bridge.

 

[Wildman]

Yes, A/C takes power to run, as does every other engine driven accessory. Engine Masters covered this with what takes how much power (engine driven cooling fan w/ clutch is like 7-10 hp). I think Myth Busters covered the topic of A/C and MPG and showed that below 45 mph, A/C off and windows down was better for MPG, above 45 windows up and A/C on.

Which is why swapping to the Tarus fan was popular on the 4 banger YJ & TJ's.

 

[TheBoogieman]

Which is why swapping to the Tarus fan was popular on the 4 banger YJ & TJ's.

It still won't help those poor 4 little squirrels from getting really tired, running on the fan belt to turn it.

 

[TheBoogieman]

As others have said, it’s true.

In my 2.5, I sometimes switch off the AC for a minute in order to avoid downshifting up hill in traffic.

You should drive my Scion XA 1.5L auto, uphill with the AC on. Your 2.5L is a BEAST!
p.s. But I get 38 mpg with the AC on. It's my $3,000 solution to Biden.

 

[SSTJ]

Which is why swapping to the Tarus fan was popular on the 4 banger YJ & TJ's.

Was this actually a good idea, and did it help? I'm interested.

 

[Wildman]

Was this actually a good idea, and did it help? I'm interested.

I did it on mine when I still had the 4 popper and yes, my butt dyno noticed a difference. You have to get some parts from other cars to make it all work well. But it's been too long since I'd done it, so I don't remember what exactly. It was a heavy-duty relay from a BMW or Volvo I think and a sensor or something else but I'm not sure.

 

[Zorba]

This applies to most EVERYTHING in the car: headlights...

That explains all the fools I see driving after dark with no headlites - they're saving gas!

 

[Cheetokps]

Which is why swapping to the Tarus fan was popular on the 4 banger YJ & TJ's.

I thought about swapping out my fan, but mostly for the sound. I know I know, it’s a Jeep, but mg find is super loud. I live in CT not somewhere super hot, so I think an electric fan would have enough cooling

 

[BlueC]

p.s. But I get 38 mpg with the AC on. It's my $3,000 solution to Biden.

I did the same thing with a Civic when a family member wanted to buy a truck. I warned him about future (current now) gas prices, now he wants to buy it back.

 

[srimes]

I don't remember how long ago this was but one of the car mag's did a write-up on running with A/C or windows down for cooling and they found that you used less fuel then running with your A/C on and windows rolled up. Now as srimes said there is no free lunch and it takes HP to turn the A/C compressor.

Good point. On aerodynamic cars the drag loss from windows down at highway speeds is more than the loss from running A/C. At low speeds this switches. No idea how this works on a TJ with its aerodynamics.

 

[Wildman]

Good point. On aerodynamic cars the drag loss from windows down at highway speeds is more than the loss from running A/C. At low speeds this switches. No idea how this works on a TJ with its aerodynamics.

Yep, since it's a brick already who knows if it matters. And I had full doors for mine but never used them, so I sold them. Soft top and half doors I'm sure don't help matters either.

 

[freedom_in_4low]

I thought about swapping out my fan, but mostly for the sound. I know I know, it’s a Jeep, but mg find is super loud. I live in CT not somewhere super hot, so I think an electric fan would have enough cooling

Have you driven a JL/JT? Holy moly, that's the loudest fan I've ever heard. and it's electric.

 

[Cheetokps]

Have you driven a JL/JT? Holy moly, that's the loudest fan I've ever heard. and it's electric.

Really? No I haven’t. I always hear about the post-tj Jeeps being way quieter overall. Good to know, maybe the electric fan wouldn’t be quieter

 

[Artsifrtsi]

Have you driven a JL/JT? Holy moly, that's the loudest fan I've ever heard. and it's electric.

The standard fan is barely noticeable... The AUX fan however... Had it kick on for the first time in Moab, thought the truck was rigging for hover mode! Lots of noise, and billowing dust!

 

[NashvilleTJ]

Really? No I haven’t. I always hear about the post-tj Jeeps being way quieter overall. Good to know, maybe the electric fan wouldn’t be quieter

I run an e-fan, and it is a hell of a lot louder than a stock engine driven fan.