Summer Heat is killing my MPG... - Fuelly Forums

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Old 08-10-2008, 07:46 AM   #1
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Summer Heat is killing my MPG...

I have tried not using the A/C but the heat makes me want to melt in my suit. So the A/C has become a must. The humidity is also killing us at 85%+. Is anyone having this issue with the A/C being necessary? We also have a baby and when she is in the car the A/C stays on.

-Nate
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Old 08-10-2008, 08:20 AM   #2
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for me the a/c affect is minimal. in fact i recently set a record trip while using a/c.

certainly the negative affect on FE varies from car to car and driver to driver.

if you have a child and/or need to keep from sweating, that's your choice to make.
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Old 08-10-2008, 09:25 AM   #3
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Have your ac system checked.

The compressor in the tracker is on its way out. You shouldn't be able to hear the ac running at all and you can hear mine. On the freeway I can be doing 55mph and by turning off the ac and keeping the same throttle opening I get 67mph. Lots of energy is wasted in that dying compressor.

Also, try a hydrocarbon refrigerant like ES-12a.

It isn't legal in the states but on my old car I charged with 1 can of 134a(to carry the compressor oil) in the system and then topped it off with propane until the low side read 35psi at idle. I couldn't really tell the ac was on anymore and i easily got 45degree air out of the vents on a hot texas summer day. The reduced load comes from the fact that 134a runs about 230psi on the high side and propane with 134a runs about 150-175 psi.
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Old 08-10-2008, 09:41 AM   #4
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Originally Posted by dkjones96 View Post
Have your ac system checked.

The compressor in the tracker is on its way out. You shouldn't be able to hear the ac running at all and you can hear mine. On the freeway I can be doing 55mph and by turning off the ac and keeping the same throttle opening I get 67mph. Lots of energy is wasted in that dying compressor.

Also, try a hydrocarbon refrigerant like ES-12a.

It isn't legal in the states but on my old car I charged with 1 can of 134a(to carry the compressor oil) in the system and then topped it off with propane until the low side read 35psi at idle. I couldn't really tell the ac was on anymore and i easily got 45degree air out of the vents on a hot texas summer day. The reduced load comes from the fact that 134a runs about 230psi on the high side and propane with 134a runs about 150-175 psi.
I don't recommend running an explosive mixture in your a/c. It can be dangerous for subsequent people working on your a/c and who knows what might happen if you had a refrigerant leak - you may have an engine fire on your hands.

-Jay
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Old 08-10-2008, 10:40 AM   #5
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I don't recommend running an explosive mixture in your a/c. It can be dangerous for subsequent people working on your a/c and who knows what might happen if you had a refrigerant leak - you may have an engine fire on your hands.

-Jay
I don't agree with that.

First, a tank of gas holds between 80-320 pounds of gasoline(a VX to an SUV). Each gallon of gasoline is 8 pounds so 1/8th gallon of gasoline is all you need to get 1 pound of fuel into the engine bay should something happen to the EFI system which will happen very quickly. You only typically have 1-1.5 pounds of propane in the AC system and propane has 74% of the energy content gasoline does.

Second, propane requires an ignition source greater than 975 degrees to ignite while gasoline requires as little as 450-500.

Third, propane is a light gas, if it leaks, it quickly dissipates into the air and gets too lean to ignite while gasoline vapors are heavy and tend to stick around.

Fourth, 134a is flammable. It requires only 350 degrees at 5psi and while it does require 1400 degrees at 0psi the oil in the ac system is very happy to light much lower than that as it is being sprayed out of the system which will light the gas.

Thank you EPA for educating us Americans. It's funny how in Europe hydrocarbon refrigerants aren't as dangerous as they are here in America.
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Old 08-10-2008, 10:47 AM   #6
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I just roll the windows down a bit and change clothes at work so I don't cook on the drive to work. But with that humidity... not sure if a portable dehumidifier will make a difference. A/C sounds like the only option. Just try to pulse it -- set vents to recycle, blowers to max and use the A/C for a bit, turn off the A/C, turn it back on later, repeat.
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Old 08-10-2008, 12:33 PM   #7
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Originally Posted by HondaTorneoSiR View Post
I have tried not using the A/C but the heat makes me want to melt in my suit. So the A/C has become a must. The humidity is also killing us at 85%+. Is anyone having this issue with the A/C being necessary? We also have a baby and when she is in the car the A/C stays on.

-Nate
I am going to tint my windows. one can cut half the heat coming into the cabin with tint. I am also considering putting reflective film on the roof of my hatch for the same reason. keep the heat out and one will not need to remove it.
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Old 08-10-2008, 09:46 PM   #8
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Also, try a hydrocarbon refrigerant like ES-12a.
Don't mix refrigerants. Now both are contaminated. HC refrigerant transports R12 and R134a oils.
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Originally Posted by Jay2TheRescue View Post
I don't recommend running an explosive mixture in your a/c. It can be dangerous for subsequent people working on your a/c and who knows what might happen if you had a refrigerant leak - you may have an engine fire on your hands.
HC is quite safe as a refrigerant and much more efficient than R134a. It isn't explosive because it doesn't have any oxygen in it. Fires and explosions from leaks are highly unlikely. HC refrigerants are banned federally and in some states because it is theoretically possible to create unexpected explosive conditions and with enough usage sooner or later someone would accomplish it. Service hazards are minimized by proper labeling. HC refrigerants are really easy to get rid of. Hook to vacuum line and idle, unless another refrigerant is mixed with it.
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Old 08-11-2008, 07:18 AM   #9
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Quote:
Originally Posted by dkjones96 View Post
First, a tank of gas holds
It doesn't matter...every mechanic and accident scene responder knows to expect explosive liquid/vapor from the gas tank. They all expect air conditioning systems to have R-134a or similar.

Quote:
Third, propane is a light gas, if it leaks, it quickly dissipates into the air
...but there's a limited amount of air in the engine bay and it's pretty captive unless the car is moving and is very un-aerodynamic under the engine bay.

Quote:
Fourth, 134a is flammable. It requires only 350 degrees at 5psi and while it does require 1400 degrees at 0psi the oil in the ac system is very happy to light much lower than that as it is being sprayed out of the system which will light the gas.
Well now THAT is interesting...
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Old 08-11-2008, 07:39 PM   #10
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1) Baby>fuel economy any day. Take care of your kid first. I grew up in Phoenix, and I can't tell you how many times per year we got news reports of a baby dying in a hot car (not as often as kids drowning in pools, but there were a bunch of them).

2) Baby aside, you could just buy a non-AC car. Now you don't have to worry about the AC issue at all.... If you live in a dry climate like the southwest, you could buy or DIY an evaporative system if you want. Iv'e seen a bunch of them from window mounted units like you saw on 50's and 60's vintage cars, to portable misting systems mounted near open windows to cool the incoming air.... Tinting windows is a MAJOR help as well. Go as dark as you legally can. Usually you can do the rear windows darker than the front. If you don't mind your car looking like a kid car or a gangster car, run the visor tint down as far as you can, and also run a "lower visor" or dash covering tint at the bottom of the windshield... or at least install a light color dash cover. Keep the dash cool and the rest of the car will stay cooler. You almost can't buy a car in AZ without it having tinted windows these days.

3) There used to be a perfectly legal R-12 alternate called Frigic. It was a propane based refrigerant designed as a direct replacement for R-12 for those who didn't want to spend the money to convert to R-134. I put it in my old Toyota truck and was blowing 35 degree air in Phoenix in August. It worked that well. I have no idea if it is compatible with 134 systems or if it's even around still, but it might be worth looking for.

4) I may be wrong on this but growing up in hot country, we always ran the AC on fresh air for the first few minutes (since outside air was cooler than the hot car) then once the car was cooled down, we switched to recirc... Since the inside air is cooler, it should take less energy (...less compressor-on time) to keep at a comfortable temperature. That SHOULD equate to some fuel savings if you can use recirculate without locking your compressor on 100% of the time.
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