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Discussion Starter #1
First hot day of the season. Took a 25-mile drive, mostly interstate.

Had the A/C on, noticed a huge reduction in power. I don't think I've ever had a vehicle that exhibited such a noticable impact from having the A/C compressor engaged.
 

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And gas mileage, i get 17-18 around town, 25 to 50mph, and if we have a hot spell where I'm doing the same driving with the AC i get around 14. My gas mileage went up a lot when I put the Magnaflo and the K&R intake with a throttle body spacer, but the AC still robs the power, even after mods.
 

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Discussion Starter #3
Maybe a retrofit with a modern compressor would help?
 

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The one thing that I've heard about, is modern cars have a relay that shuts the compressor down at a certain power, so that when your pulling up a long interstate hill the compressor would shut off. Basically a relay that shuts the compressor down when you need power most. This relay started showing up at around 2000, but is standard these days. I don't know how it could be done, on ours, but it's been done before on others. We need an Electrical Engineer stat!
 

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I've had a '98 Frontier for 13 years now, and a 2004 Frontier for 5 years; both are 4-cylinder 5-speeds, and I don't notice the same. Mine are the original compressors, and the AC gets used a ton here in Arizona. It's not like I have a practice of turning off the AC to go up hills either.
 

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I love the way my truck responds when I hit the pedal, but there is no doubt I feel like I'm driving in mud when the AC is on.
 

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I use the ac like an engine brake if I'm going down a steep hill it will definately slow me down so I can use less brakes

Same if I'm pulling out onto the highway, I turn it off right before I take off so I don't slow everybody down

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BigDad said:
I love the way my truck responds when I hit the pedal, but there is no doubt I feel like I'm driving in mud when the AC is on.

I use the ac like an engine brake if I'm going down a steep hill it will definitely slow me down so I can use less brakes

Same if I'm pulling out onto the highway, I turn it off right before I take off so I don't slow everybody down

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Maybe get a 4-cylinder 5-speed 2WD truck? I know my daughter's 4WD '98 Pathfinder with VG33 and automatic is no racehorse, but figured extra weight of 4WD and Pathfinder body had something to do with it. A co-worker who had a 2002 4-cylinder Frontier King Cab with automatic claimed his was a dog as well; maybe the automatic transmission shift points????
 

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Was just looking at numbers and was very surprised. The L4 in a 2wd extended cab 5 speed, has almost the same HP to weight ratio as the V6 with auto and 4 WD. I have been looking for another 1st gen, and I will think about the L4 with 5 speed, and had not even considered it before.
 

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maybe the automatic transmission shift points????
Had to go to a graduation party and it's about 95 here, so I manually shifted my trans at about 200 rpm's above the auto shift points, huge difference! That little bit bogs it down just enough, doubt I will bother, but if I ever need trans work, I might look into it.
 

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I drove my 2004 King Cab 2WD 4-cylinder, 5-speed 200 miles yesterday, mostly on highways (this weighs more than my similarly-equipped '98 regular cab). So I intentionally tried turning the AC off and on while driving, on straightaways, downhills, and uphills, and if I didn't know I was pressing the button, I wouldn't have had any idea whether AC was switched on or off.

So my guesses for the difference - which I do believe are real - are still:
...automatic transmission design
...engine design
...are the same AC compressors used on the two engines?

Maybe someone with a manual transmission and the V6 can comment about whether they have the same issue.
 

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Last week I did a 500 mile RT including some lower elevation passes. One 6% grade had me down in third gear, once; otherwise fourth handled them all. But I turned the air off on long or steep uphill grades. There's no way the truck would sustain 75mph speed limit with the A/C on on even moderate grades.

On steep downhills I always turn the air on in warm weather too.
 

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Yes, sometimes on steep uphill highway grades I do have to downshift into 4th gear on mine. On highways I typically use the aftermarket Rostra cruise control in my 2004.
 

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My aftermarket CC will disengage when the speed differential gets too great. Set at say, 79mph, when the truck slows to 64mph on a grade the cruise will disengage. At that point it's time to shift down into 4th gear anyway so it works out well.
 

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Ac power reduction.

First hot day of the season. Took a 25-mile drive, mostly interstate.

Had the A/C on, noticed a huge reduction in power. I don't think I've ever had a vehicle that exhibited such a noticable impact from having the A/C compressor engaged.
When I first purchased my 2004 2.4 XE I hardly noticed the ac kick in. But over the last few years it felt like it was robbing half the limited hp the truck has. I charged the ac refrigerant and now it feels like a different truck. I think overtime the hoses degrade and you slowly lose refrigerant. This low level of refrigerant causes the ac to cycle constantly when your ac is on and robs hp.
 

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I'll have to double check my facts, but I believe the fan clutch may play a part in this as well. If it's hot enough for the compressor to run non-stop, or disengage all together, than it's a safe bet it's hot enough for the clutch to engage. The two of them acting together would cause a very noticeable drop in both hp and gas mileage.
I'm told converting to an electric fan does wonders.
 

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I remember an article some years back in Car and Driver I think. The horsepower cost of running the A/C compressor is about 10-14HP on average. That would cause a noticeable difference with A/C on or off in almost any vehicle. I know that my 4-banger has a compressor cutout. At about 75% throttle, the compressor cuts off until you back off the throttle. I don't know if the V6 does the same, but I would assume so.
 
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