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Old 10-31-2012, 10:43 AM   #1
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Remote start may lower gas mileage

Those whose Jeeps have REMOTE START AND AUTO A/C. If you REMOTE start you vehicle the center a/c control knob push function (a/c on/off) is USELESS. The little light may go off and on as you push the knob but your a/c is ON. If you want plain outside air or plain heated outside air you are out of luck as your compressor will cycle on/off anyway. To regain function of the a/c on/off button you have to turn off the car for about 15 minutes then restart with the key MANUALLY.

So...if you plan REMOTE starting your Jeep this winter with the heat preset so you can begin your cold morning drive in a warm Jeep you will have a warm Jeep and have your a/c compressor cycling as well. That way you will have consistant gas mileage all year (yup...that was sarcasm).

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Old 10-31-2012, 01:22 PM   #2
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Old 10-31-2012, 01:26 PM   #3
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Old 10-31-2012, 01:29 PM   #4
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Old 10-31-2012, 01:41 PM   #5
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wait..... huh? I read that about 5 times and still don't really understand what your sayin. Either way I don't have remote start and auto a/c / heat. Consider yourself lucky just to have heat and air in a jeep. No need to get too picky
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Old 10-31-2012, 02:02 PM   #6
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He is exactly correct. I didnt chalk it up to relating it to remote start, but since i do it everyday, it probably is. Never could get vent air myself...
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Old 10-31-2012, 02:10 PM   #7
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I will have to check this out. I don't seem to recall having an issue switching from auto to regular vents, even after using remote start. However, often my vehicle has stopped running by the time I get into it, so it could make a difference...

However, I don't care in terms of gas mileage. I didn't buy this vehicle expecting to pay less in gas than I did in my Pontiac...
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Old 10-31-2012, 03:07 PM   #8
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I HATE when people type like THIS to get a point across. We can READ and typing like that just PISSES off NORMAL people.


Italics were invented for a reason.
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Old 10-31-2012, 03:43 PM   #9
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For a little more detailed explanation, refer to this thread, where I too, TALK like THIS!

PS, I hate when people type with italics, or people that have time to hate stupid crap.

http://www.wranglerforum.com/f33/att...mp-196566.html
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Old 10-31-2012, 03:50 PM   #10
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Just to state the obvious, any time the Jeep is running and the wheels aren't turning, you're lowering your gas mileage.
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Old 10-31-2012, 08:04 PM   #11
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Originally Posted by SinCityJets View Post
PS, I hate when people type with italics, or people that have time to hate stupid crap.
You mean stupid crap like the AC compressor running all the time? It runs about 90% of the time with manual start and AC just to keep the oil circulated anyway.

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Originally Posted by JTE View Post
Just to state the obvious, any time the Jeep is running and the wheels aren't turning, you're lowering your gas mileage.
This. And the AC compressor running or not isn't going to make that much difference in how much lower it gets.
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Old 10-31-2012, 11:09 PM   #12
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Now this has turned out great. We have now all learned that THIS is called italics as opposed to capitalization. Someone else who has no interest in this subject is bored and wants us to know it. Another person who does not care about gas mileage anyway. Another person does not have remote start or auto a/c but feels they aren't necessary on a Jeep. And Oilwell....who hopefully has his/her Jeep jacked up by the frame at night with the engine running with a/c on and in gear with 4 wheel drive on and lockers engaged so the trany, engine, a/c compressor, front/rear diffs and power steering fluids are all circulating for lubrication sake. Keep your refrigerator slightly open as well to keep that compressor running and well lubed. Leave a faucet running in your house 24/7 if you have your own well to keep that pump running and in prime condition as well. WOW.......informaton overload !!!!
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Old 10-31-2012, 11:24 PM   #13
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Your a/c compressor runs on defrost because it removes humidity from the air, if it didn't do this it would take forever to clear the windshield. If it would even clear it
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Old 11-01-2012, 01:06 AM   #14
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I could be wrong but the only reason the a/c compressor comes on with the heat is to keep the compressor from seizing up from lack of use in the winter. The air coming in from the inside of the Vehical is not blowing across the evaporater core. It's blowing across the heater core. I have had a few older vehicals without a/c and the defrost fuction worked just fine without a dehumidifier.
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Old 11-01-2012, 01:21 AM   #15
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It's been proven many times that running the a/c uses very little fuel in modern systems. People who drive with their windows down at 55 mph or faster actually consume more fuel than running the A/C. At idle for a few minutes every day you wont even notice the drop in economy.
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Old 11-01-2012, 02:19 AM   #16
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To add a few cents here, I notice my ac compressor cycling with the heat on and ac button off. Mind you, I have the auto climate control so I just chalked it up to being something about the auto climate control.
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Old 11-01-2012, 05:51 AM   #17
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Don't now about jeep but when I worked on fords the a/c comp would come on with the heat in any mode but vent. It did not matter if it was manual or auto climit control.
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Old 11-01-2012, 08:56 AM   #18
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Quote:
Originally Posted by bsps1111 View Post
Now this has turned out great. We have now all learned that THIS is called italics as opposed to capitalization. Someone else who has no interest in this subject is bored and wants us to know it. Another person who does not care about gas mileage anyway. Another person does not have remote start or auto a/c but feels they aren't necessary on a Jeep. And Oilwell....who hopefully has his/her Jeep jacked up by the frame at night with the engine running with a/c on and in gear with 4 wheel drive on and lockers engaged so the trany, engine, a/c compressor, front/rear diffs and power steering fluids are all circulating for lubrication sake. Keep your refrigerator slightly open as well to keep that compressor running and well lubed. Leave a faucet running in your house 24/7 if you have your own well to keep that pump running and in prime condition as well. WOW.......informaton overload !!!!
Are you always this much of a tool, or did you wake up with your knickers in an especially large crusted bunch this morning?

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Your a/c compressor runs on defrost because it removes humidity from the air, if it didn't do this it would take forever to clear the windshield. If it would even clear it
This is false as someone else already mentioned. If you have cold air of a given humidity and heat it up the humidity will drop by itself. It doesn't need help from the AC to do that.

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I could be wrong but the only reason the a/c compressor comes on with the heat is to keep the compressor from seizing up from lack of use in the winter. The air coming in from the inside of the Vehical is not blowing across the evaporater core. It's blowing across the heater core. I have had a few older vehicals without a/c and the defrost fuction worked just fine without a dehumidifier.
Where the air goes depends on the vehicle. Most blow it across the evaporator and heater core all the time to simplify the system.
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Old 11-01-2012, 09:37 AM   #19
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Click image for larger version

Name:	RTFM.jpg
Views:	168
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ID:	174237
Defrost


Air is directed through the windshield and side
window demist outlets. Use this mode with maximum
blower and temperature settings for best windshield
and side window defrosting.


NOTE:
The air conditioning compressor operates in
Mix, Defrost, or a blend of these modes, even if the Air

Conditioning (A/C) button is not pressed. This dehumidifies
the air to help dry the windshield. To improve

fuel economy, use these modes only when necessary.


DB
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Old 11-01-2012, 09:46 AM   #20
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^^^^^^^^^^. Once again I could be wrong but if air is blowing over a evaporater and a heater core you would not have any control over the temp of the air comi g out of the vents. One is going to cool the air and the other is going to heat it. It would never work. The only systems I have ever Seen do this is aux systems for busses and ambulances. They have water valves on them you have to open or close depending on if you want heat or cooling. I'm am very interested to see what jeep says about this. I have been a mechanic for 20 plus years and every Vehical I have ever worked on the system works like this. If they did not cycle the comp in the winter they would all seize up. And as far as the a/c light coming on. It does not make a diferance in how how the heater functions. My excursion does the same thing with the EATC. I think it does that so if you start the car and the temp is above what the controles are set at it will start cooling the Vehical.
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Old 11-01-2012, 11:36 AM   #21
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Personally, I am interested in the topic and everything that everyone has to say on it. My 2013 JKR has auto temp controls and remote start...and I use the remote start routinely.

That said, there really is no reason to be jerks to each other here. We can offer info and participate in a dialog building on what others have said without needing to establish a winner...or pulling out measuring tapes.

Now back to the discussion...to which I have pretty much nothing of value to add.
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Old 11-01-2012, 12:33 PM   #22
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I use remote start 2ft away from my vehicle because my 7 year old believes if he rubs the door gently Greta will wake up and start. Now my choices seem to be, break the environment, or break my 7 year old's heart when I have to tell him that Greta isn't actually a magical vehicle that loves him.

Sorry guys, the 7 year old wins. I guess you better start your climatic Apocalypse planning because my AC will always be running.
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Old 11-01-2012, 01:06 PM   #23
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Originally Posted by oilwell1415 View Post
Where the air goes depends on the vehicle. Most blow it across the evaporator and heater core all the time to simplify the system.
Just to clarify, I'm saying that there are not two separate systems for heat and air, the evaporator and heater core are in the same system. If it's on full hot the air comes in and goes over both of them. If you select anything other than full hot it diverts part or all of it away from the heater core.

Quote:
Originally Posted by Dick Blonov View Post
Attachment 174237
Defrost

Air is directed through the windshield and side
window demist outlets. Use this mode with maximum
blower and temperature settings for best windshield
and side window defrosting.


NOTE:
The air conditioning compressor operates in
Mix, Defrost, or a blend of these modes, even if the Air


Conditioning (A/C) button is not pressed. This dehumidifies

the air to help dry the windshield. To improve


fuel economy, use these modes only when necessary.


DB
Don't know where that came from, but they can say whatever they want to say and it doesn't necessarily make it right. Running the compressor when it's cold outside doesn't do anything for the humidity. If it did you would see condensate running out, but you don't see that. The simple act of heating 30 degree air at 50%RH to 160 degrees will put the RH in the single digits. No help from the compressor is required.
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Old 11-01-2012, 01:11 PM   #24
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Quote:
Originally Posted by oilwell1415 View Post
Don't know where that came from, but they can say whatever they want to say and it doesn't necessarily make it right. Running the compressor when it's cold outside doesn't do anything for the humidity. If it did you would see condensate running out, but you don't see that. The simple act of heating 30 degree air at 50%RH to 160 degrees will put the RH in the single digits. No help from the compressor is required.
That came from the 2012 owners manual...
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Old 11-01-2012, 01:21 PM   #25
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That came from the 2012 owners manual...
I know that, but where did they get it? It's not true and there's no reason for it to say that. Blowing cold air over an evaporator that's only a few degrees colder won't do anything. It will cut the humidity of hot air that is being cooled, but doesn't work the other way. Sounds like the marketing guys got their hands on manual to explain away why the AC compressor runs all the time.
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Old 11-01-2012, 01:36 PM   #26
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The mpg of an idling vehicle is 0 mpg. Extended idling on a daily basis will lower your fuel economy.

The info Dick Blonov posted is essentially correct.



As someone who has trained in automotive AC, it isn't black magic. Just that some folks have no knowledge of the system.

Perhaps I can clear up some of the misunderstanding.

On the JK, the evaporator core (acts as a heat exchanger) and heater core are enclosed in a plastic box. Attached to the box are various air ducts, doors, and the blower motor. The box is commonly referred to in the industry as the HVAC module (Heating/ventilation/Air Conditioning). The doors are controlled by electric motors. Depending on the settings, air can pass thru both the evaporator and heater core.

In the front of the HVAC module, closest to the firewall is the evaporator. Right behind it is the heater core. The heater core is about half the size of the evaporator. A door separates the two. With the engine running, coolant is always flowing thru the heater core.

Unless the blower motor fan speed knob is set to "0", air is always moving thru the HVAC module.

The pressure of a gas is directly related to the temperature. In an automotive AC system at rest (AC turned off) the pressure will increase/decrease as the outside air temp increases/decreases. Laws of physics. Automakers, Jeep included, design their systems so when the outside air temp drops below about 40F, the compressor will not cycle on even if the AC button is pushed. There are two primary reasons for this: 1) Prevents the evaporator from getting so cold that moisture from the incoming air freezes on it and causes icing. 2) Prevents compressor damage because the system pressure is too low.

Air always has moisture in it. The amount of moisture in the air is expressed as “relative humidity” (RH). In arid regions of the US, Canada, and Mexico the RH may be less than 10%, meaning the air is extremely dry. In more humid areas, the RH can approach 100%. When precipitation is falling (rain/snow/sleet/hail), the RH usually increases.

When cool air is pulled into a vehicle by the blower motor, the moisture may condense on the inside of the windows and cause fogging. Also a law of physics: as air is cooled (temp decreases), moisture vapor in the air will condense into liquid. The evaporator does the same thing. With the AC compressor cycling, the evaporator gets cold. As outside air passes thru the evaporator, it gets cooled and the moisture condenses out. We will see how this comes into play later.

Let’s look at a few scenarios of how the system works. We will assume the outside air temp is 45-50F, the fan speed is not on "0", and the engine is at normal operating temperature.

1) Driver selects vent mode/no heat/no AC: Air from the blower motor flows thru the evaporator core which is the same temp as the outside air. The heater core door is closed so the air bypasses it and exits from the vents on the dash.

2) Driver selects vent mode/partial heat/no AC: Air flow from the blower motor flows thru the evaporator core which is the same temp as outside air. The heater core door is now partly open because the driver turned the heat knob to the middle position. Some of the incoming air is now directed over the heater core and warms up. Warm air exits the dash vents.

3) Driver selects vent mode/full heat/no AC: Same as #2, but the door for the heater core is fully open so all incoming air passes thru the heater core. Hot air exits the vents.

4) Driver selects defog mode/no heat/no AC: Since the outside air temp is above 40F, the compressor will cycle on and off (less than during normal AC operation) to cool the evaporator. Air from the blower motor passes thru the evaporator and is cooled and dried because some of the moisture is condensed out. The heater core door is closed so cooler dry air exits the defroster/floor vents.

5) Driver selects defog mode, partial heat/no AC: Same as #4, except some of the cooler dried air from the evaporator now passes thru the heater core and gets warmed up. Warm dry air exits the defroster/floor vents.

6) Driver selects defog mode/full heat/no AC: Same as #4 except the heater core door is fully open and all the air from the evaporator passes thru the heater core and gets heated up. Hot dry air exits the defroster/floor vents.


Hope this helps.
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Old 11-01-2012, 01:55 PM   #27
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^Thanks for the detailed explanation. But I guess I still don't understand why there is a lack of driver control over the compressor when Remote Start is used.
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Old 11-01-2012, 01:59 PM   #28
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My thinking is the compressor automatically cycles with remote start so the driver doesn't go out to his/her Jeep and find the windows all fogged up inside.
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Old 11-01-2012, 02:14 PM   #29
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So what happens if you leave your heat set to "off" and use remote start?

I usually turn everthing to off before I leave my vehicle. And I usually start my vehicle with everything off (hot or cold). I let it run for a few minutes before I switch on the heat or AC in really bad weather.
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Old 11-01-2012, 02:31 PM   #30
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It will turn on the A/C for you. Your settings are irrelevant when you use the remote start on a 12+. Go try it!

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