Running AC Compressor loss of engine power.

Symptoms: Running with AC on seems to suck a lot of power from the engine. I would expect some but this seems excessive. AC runs nice and cold.

Details: 99xj, AW4, 33x10.5x15 KO2s, 4.56 gears. I6.

Best way to describe is when accelerating it feels like someone tapped the brakes a bit when the compressor cycles.

Thoughts?

Yep, that's how it goes. Running the AC in all my vehicles I can tell there is a decrease in engine power. In the TJ you can actually feel the compressor kick on and off as you drive, and it feels like it slows down just as you describe.

CarbonXJ said:

Yep, that's how it goes. Running the AC in all my vehicles I can tell there is a decrease in engine power. In the TJ you can actually feel the compressor kick on and off as you drive, and it feels like it slows down just as you describe.

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I'm thinking pretty normal as well but wanted to see what others are saying. I don't feel any loss in power in our other car but it is not a Jeep. Need MO POWER!

You should feel some drag on the system, however really severe drain on power may be the compressor about to bite it.
When off and cool to the touch try turning the compressor by hand see how much resistance you have. I can't think of a better test for this, but shouldn't feel like someone taps the brakes.
Is the compressor excessively noisy?

It is hard to say going by words, some resistance is normal. I'm concerned it might be too much.

I can notice in all of our vehicles when the compressor kicks on, even the v8 truck, the resistance is why ac hurts gas Mileage. Maybe it usual for the size tires and gears.




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Check your system pressure, perhaps overcharging could cause it to become more noticeable.

Just for reference, most AC systems pull around 15 hp.

What happening could be normal, it's hard to tell over the forum with written words.

What makes me concerned when anybody mentions a bad drag on the Engine when compressor kick in is I know people who ground compressors to the ground burning out everything and locking it up. Literally smoked the belt until it broke. (That how long ago it was the car had v belts)
Yes they were stupid, negligent, dumbass to say the least and even with a ton of work the ac never worked right in that car again.

I've heard of stories of big engines being destroyed by a compressor locking up,

Some drag on the engine is normal, this probably is as well. Do to my experience I am always jumping over a compressor problem before it gets bad.



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Well, when the compressor craters, it's time to tear the dash apart to the firewall to reach the evaporator, change the accumulator, and flush/replace the condenser. This is more than most people want to do, so the system never quite works the same and money for a new compressor and charge is pissed into the wind shortly thereafter.

Overland said:

Well, when the compressor craters, it's time to tear the dash apart to the firewall to reach the evaporator, change the accumulator, and flush/replace the condenser. This is more than most people want to do, so the system never quite works the same and money for a new compressor and charge is pissed into the wind shortly thereafter.

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I'm part of the problem is aftermarket parts are almost never work up oem standards. So even taking apart and replacing lines, dryer, evap and condensers it may never work right again, especially old r12 systems and/or old Germans cars .


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old_man said:

Just for reference, most AC systems pull around 15 hp.

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Wow....15hp is a lot. I was thinking it was more like 5hp. After driving yesterday I am not sure the issue is with AC. I ran with AC on and it seemed just fine. You could tell when it came on but it really did not affect engine performance.

I think when it is really hot out or the under hood temps are high the mech fan is locking up killing the engine power.

Green Mesa XJ said:

I'm part of the problem is aftermarket parts are almost never work up oem standards. So even taking apart and replacing lines, dryer, evap and condensers it may never work right again, especially old r12 systems and/or old Germans cars .


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There are good and bad parts, and good installs and bad installs. I will always adhere to the "it's all in the prep work" doctrine. My 87 Ranger has 273k and only the compressor is original for its R12 system; and I still run R12. Still does this to the AC


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I've got one car, my baby, perfect shape still has the original r12 system. That car gets cold fast! Almost forget how good r12 was. The worst r134a car I had was adapted as a afterthought by Honda (year before was r12) by the time I got where I was going it finally beginning cooling the cab off. Any trip longer than 30 min was well cooled.

More modern cars may be easier to keep ac in good running shape. A lot of cars from the late 70s were bolt on crap at individual dealers, or last minute additions by carmakers who didn't have ac in their base models in Europe and needed to compete in the USA.

The car I was talking about was given to me as my fist car, just had to fix it up. I pulled the dash, replaced everything. The compressor was a afterthought and not in the books. Had to take it to a ac shop for them to look it up. Did all that work with a neighbor who worked in ac. It ended up working but it never was to par. A cheap car, cheap parts, bad design with almost no aftermarket support.
I doubt that trifecta is going to be replicated any time soon.
All the jeeps I've repaired the air on have been great, all the new parts some NOS mopar worked great.


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