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Old 09-29-2018, 09:50 AM   #1 (permalink)
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HCH1 +20mpg loss with AC on

I recently purchased a cheap, high mile, manual 2005 Civic Hybrid that I've been bringing back to life. I got the check engine lights and IMA light taken care of and auto-stop is back. It's been running great and mpgs have jumped up considerably.

One issue I've noticed is that the AC absolutely kills my mileage. I can generally achieve +60mpg on my daily work commute without the AC. Meanwhile it's difficult to even hit 40mpg with the AC on. I know air conditioning is going to eat mileage, but that seems incredibly excessive.

Is this consistent with what others are seeing or is there something i should take a look at? I realize "turn the ac off" is going to be the popular answer, but it's really not an option during the summer driving to work in South Florida.

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Old 09-29-2018, 12:21 PM   #2 (permalink)
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Turn the AC to a warmer temperature and it'll cycle the compressor off more. That'll help a bit.

The HCH1 uses an engine-driven compressor like regular cars, instead of an electrically-driven compressor like many other hybrids. You may be able to do a pulley swap to underdrive the AC some and reduce its drag on the engine. I've never looked into that though, and the pulley on the compressor is pretty distinctive, not to mention a bear to get at. It wouldn't be like swapping a V-belt pulley on a small block Chevy engine, I'm not sure if the right kind of parts are even available.

When my AC comes on it pulls a pretty noticeable amount of power, sufficiently cutting into what the engine provides that I turn the AC off when climbing some of the longer hills in my area. It makes the difference between shifting down one gear, or two.

Don't forget about setting it to Recirculate and turning the ECON button ON. ECON will allow the engine to turn off at lights, otherwise if you have the AC on the engine will keep running. At short lights a brief pause won't be too bad, but at longer ones it might be more than you can tolerate.

If your windows aren't already tinted to block as much IR as possible, now's the time to consider it.
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Old 09-29-2018, 01:46 PM   #3 (permalink)
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If you use the brakes a lot or moderately, you could add a relay that only engages the ac compressor when the brakes are applied, or you could somehow hook it up to battery regen. So it is only doing its job then.
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Old 09-29-2018, 03:01 PM   #4 (permalink)
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Hi pdexta,
I have a 2010 Ford Fusion hybrid. It has an electric A/C and I get about the same mpg hit during the hottest days. My usual daily commute gets me 49 to 50 mpg. During the worst days this summer (reported high 115 deg. but the temp sensor in the car while on the freeway read 122) the mileage dropped to 35.
I also take a hit when it's cold. I doubt the heater has any effect on economy, but the colder, denser air does.
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Old 09-29-2018, 10:45 PM   #5 (permalink)
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That sounds about right. The AC absolutely murders the HCH1 MPG. You can't maintain lean burn at most speeds.
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Old 09-30-2018, 12:45 AM   #6 (permalink)
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60 mpg is pretty exceptional for an HCH1. You're either a very good hypermiler, or you have a very inaccurate mpg meter.

Regardless, to get that kind of mileage, you must be at a very low average power... probably on the order of 9-12 hp. A/C consumes about 3-4 hp. You can see that's a huge % increase in power.

While you may feel compelled to use your A/C less for better mileage, consider that the battery is cooled by cabin air. I always say, "if the driver and passengers aren't cool and comfortable, the battery is being damaged."
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Old 09-30-2018, 11:14 AM   #7 (permalink)
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Thank you all for the replies. At least it doesn't sound like there's an issue with the car. Hopefully some cooler weather will roll in soon. I was planning for tint anyway, seems like that would help cool me down a bit.

Quote:
Originally Posted by S Keith View Post
60 mpg is pretty exceptional for an HCH1. You're either a very good hypermiler, or you have a very inaccurate mpg meter.

Regardless, to get that kind of mileage, you must be at a very low average power... probably on the order of 9-12 hp. A/C consumes about 3-4 hp. You can see that's a huge % increase in power.
That +60mpg reference was flat ground, with cruise set at 40-50mph. Certainly not something I can maintain over a full tank of gas or anything. The built in mpg meter has read pretty consistent with calculations at the pump (maybe 1mpg on the optimistic side). My first 2 tanks have been in the mid 40's, I think I'm a little over 45mpg on my current tank.

The HP explanation makes a lot of sense. The more efficient the car runs, the bigger % of loss you see from the AC.
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Old 09-30-2018, 01:11 PM   #8 (permalink)
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Quote:
Originally Posted by S Keith View Post
60 mpg is pretty exceptional for an HCH1. You're either a very good hypermiler, or you have a very inaccurate mpg meter.
Florida has no hills.

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