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  #1  
Old 06-22-2011, 06:18 AM
TenSilver TenSilver is offline
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Default Air Conditioning and Gas Consumption

This post rates right up there with the 101 questions you wanted to know but was afraid to ask.


Does the Ranger use more gas if the air conditioner is running and the blower motor is on high but not max ac?

My weird science way of thinking about it says more since more hot air is being drawn across the evaporator.




A Ranger friend of mine says it doesn't matter what the blower motor is set to. It would use the same amount of gas.

Post your thoughts on this folks.

This should be a fun thread!
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Old 06-22-2011, 07:11 AM
bmjwright bmjwright is offline
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Default Re: Air Conditioning and Gas Consumption

Max AC only moves the damper door from pulling outside air to using inside air, so the compressor is doing them same work and wouldn't have an effect on mpg.
The fan on high, using more electricity, will make the alternator work harder and have some effect on fuel economy. But I suspect the difference would be negligible.
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Old 06-22-2011, 07:29 AM
FireRanger FireRanger is offline
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Default Re: Air Conditioning and Gas Consumption

If the air across the evaporator coil is moving faster (higher blower setting), it can exchange more heat and the freon will return to the compressor warmer. If you have it on a lower setting or recirculating inside air, it will exchange less heat and return to the compressor cooler.

But remember there is no thermostatic control on any of this. The compressor works solely on it's output pressure. That output pressure really isn't dependent on it's incoming freon temperature. So the blower speed, max ac, etc should theoretically have no effect on this. The pressure goes from low to high due to mechanical design (expansion valves, etc).

So I think the blow speed and max ac settings effect on fuel consumption would be negligible if at any.
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Old 06-22-2011, 04:08 PM
TenSilver TenSilver is offline
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Default Re: Air Conditioning and Gas Consumption

Thanks for everyone's response!

Fireranger,
Your explanation makes sense. It juse seems that the compressor would have to work harder to chill the hotter freon, thus comsuming more gas.

So my friend was right.

Thanks!
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Old 06-22-2011, 04:35 PM
FireRanger FireRanger is offline
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Default Re: Air Conditioning and Gas Consumption

It would seem that way... except the compressor isn't chilling anything, and nothing in the AC system is operationally based on temperature. The compressor is just compressing to set pressures. It will make the pressure regardless of temperature.

The chill comes from two things. Air going across the condenser coil draws heat away from the compressed and heated freon (reducing its temperature some) causing it to condense into a liquid. Condensing gives up heat which is why air blowing over the condenser coil is hot. When that freon now goes into the evaporator coil inside the truck, it goes through an expansion valve too which causes it to expand (decompress...). Adiabatic cooling causes a steep drop in temperature which is where you get your cold from. It then goes back to the compressor and starts over.

So you see, an air conditioner actually has very little to do with temperature and very much to do with pressure. The temperature is merely a very useful side-effect that doesn't actually effect much.

The only time temperature and air flow can effect things is:
- A lack of air flow over the condenser will cause it not to condense. That's why it stops working if your engine fan isn't spinning while you aren't moving.

- A lack of air flow over the evaporator can cause it to ice up due to humidity. It doesn't actually stop the system from working though, as it remains a solid block of ice until you shut it off and let it thaw out.
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Last edited by FireRanger; 06-22-2011 at 04:39 PM.
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Old 06-22-2011, 05:08 PM
Pasco08 Pasco08 is offline
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Default Re: Air Conditioning and Gas Consumption

I always was told it didn't matter in fact when the ac is off and windows are down it creates more drag and actually hurts fuel economy.
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Old 06-22-2011, 05:10 PM
FireRanger FireRanger is offline
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Default Re: Air Conditioning and Gas Consumption

I've heard that too. Specifically at "highway speeds". Never bothered to research it since if it is cool enough to have the windows down, i put them down and don't care. A 75mph breeze is great.
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Last edited by FireRanger; 06-22-2011 at 05:13 PM.
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Old 06-22-2011, 07:44 PM
S13minus1 S13minus1 is offline
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Default Re: Air Conditioning and Gas Consumption

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Originally Posted by FireRanger View Post
But remember there is no thermostatic control on any of this. The compressor works solely on it's output pressure.
there isnt a evaporator temp sensor to cycle the compressor? what prevents the line from freezing then?
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Old 06-22-2011, 07:48 PM
FireRanger FireRanger is offline
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Default Re: Air Conditioning and Gas Consumption

There may be, I don't know if rangers have that. My guess would be no but its just a guess. None the less, if it does, that is a protection system for an abnormal condition. Not a thermostatic control in the sense that it controls how much work the system does based on how cold the air is.
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Old 06-22-2011, 07:51 PM
S13minus1 S13minus1 is offline
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Default Re: Air Conditioning and Gas Consumption

well if there is [the ranger is a pretty outdated system] it wouldnt be for an abnormal condition, thats what the line pressure sensors are for. it would tell the pcm if the evaporator is too cold [shut off compressor] or too hot [turn compressor back on] as long as both pressure sensors are within spec.

at least, thats how it works with most others
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Old 06-23-2011, 03:00 AM
TenSilver TenSilver is offline
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Default Re: Air Conditioning and Gas Consumption

Good explanation Fireranger! Thanks!
I've seen the air unit for the office at work freeze up many times.


My Ranger has an electric fan in addition to the fan on the engine. I think It's mounted behind the condenser but I'll have to look again. I assume it would run when in stop and go traffic with the air on. I don't know what years they started adding the electric fan.
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  #12  
Old 06-23-2011, 05:00 AM
TomN TomN is offline
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Default Re: Air Conditioning and Gas Consumption

My MPG's could drop to 10, Im still blasting the AC.

Love having AC.
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Old 06-23-2011, 09:24 AM
FireRanger FireRanger is offline
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Default Re: Air Conditioning and Gas Consumption

I didn't think they ever put electric fans in any ranger model or year.
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  #14  
Old 06-23-2011, 04:31 PM
TenSilver TenSilver is offline
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Default Re: Air Conditioning and Gas Consumption

^ I'll snap a photo of it tomorrow and post it here. ^
I've never seen one in a Ranger until I got this one.
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Old 06-23-2011, 04:33 PM
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Default Re: Air Conditioning and Gas Consumption

Quote:
Originally Posted by TomN View Post
My MPG's could drop to 10, Im still blasting the AC.

Love having AC.
x2...sometimes having the 3 windows open just doesnt cut it
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