When driving, what sucks more gas? A/C or heat?

[psteng19]

My guess is A/C

When I turn on the A/C and the compressor activates, I lose a ton of power.
And isn't the heat generated in the engine compartment and blown into the cabin?

 

[mAdD INDIAN]

heat doesn't suck any gas. it uses the engine's heat to warm the car. unless you have the windshield defroster running, in which case it turns on the A/C compressor so that does use gas.

 

[Zenmervolt]

The only gas heat uses is to run the fan. Heat blows air through a little radiator (the heater core) and then into the cabin. A/C has to run a compressor and all the ancillary items, plus the fans. Since the fans are electric, their impact is negligible and we really don't need to count them. The compressor runs off of a belt and takes around 5 hp IIRC.

ZV

EDIT: Defrost doesn't turn on the A/C on any of my family's car (Accord, Maxima, Explorer, 320i, and 924S). All defrost does is direct the hot air through the vents at the base of the windshield. The manuals say to turn the A/C on manually if the regular defrost isn't working well enough, but the A/C doesn't come on by itself with the defrost.

 

[Brutuskend]

AC

It uses a belt. Heat uses a electric fan...

 

[bolido2000]

AC

Driving around town it saves more gas if you open the window instead of AC. On the freeway is the opposite.

 

[Shaka]

my high school science teacher told us to use hot air for the windshield defroster. hot air is supposed to be better at drying up the condensation. but everyone seems to always use the A/C

 

[Zenmervolt]

Originally posted by: bolido2000
AC

Driving around town it saves more gas if you open the window instead of AC. On the freeway is the opposite.

Actually, it's roughly equal on the freeway.

ZV

EDIT:

my high school science teacher told us to use hot air for the windshield defroster. hot air is supposed to be better at drying up the condensation. but everyone seems to always use the A/C

People use the A/C because the A/C system removes the humidity from the air. A/C effectively functions as a dehumidifier for the car's interior, whereas the heater warms the glass to a point at which the condensation doesn't form.

 

[Pepsi90919]

using heat steals heat from the engine. this will create negligible gas consumption because the computer will try to maintain a certain temperature. key word being negligible because it's almost nothing.

a/c rapes the engine of power much more heavily.

 

[geno]

A/C - heat doesn't require for the motor to turn a compressor

 

[Zenmervolt]

Originally posted by: Pepsi90919
using heat steals heat from the engine. this will create negligible gas consumption because the computer will try to maintain a certain temperature. key word being negligible because it's almost nothing.

No, the ECU won't use more fuel, the thermostat just won't circulate the coolant as much. The car will use more fuel on startup and initial warmup, but once the engine is running temperature is a function of how much coolant is allowed to circulate.

ZV

 

[db]

Heater and A/C use the same ventilation fan.
A/C also must use the compressor, which takes more power from the engine.

A/C takes more gas, on cars which run the systems seperately (some cars automatically turn on the a/c when the heat is turned on w/the fan).

 

[JeffreyLebowski]

OK, if you own a Nissan vehicle made after 99, the deforst automatically turns on the A/C. it does this to keep the side windows from fogging up.

heat doesn't suck any gas. it uses the engine's heat to warm the car. unless you have the windshield defroster running, in which case it turns on the A/C compressor so that does use gas.

tsk, tsk. Heat that comes through your vents is not off of the engine. it comes from a heater core(like a mini space heater) since it is electric it doesn't use any "engine power"

 

[jemcam]

Originally posted by: Shaka
my high school science teacher told us to use hot air for the windshield defroster. hot air is supposed to be better at drying up the condensation. but everyone seems to always use the A/C

People turn on the AC and then turn it to heat because the AC will dehumidify the air faster. Try it next time.

 

[jemcam]

Originally posted by: JeffreyLebowski
OK, if you own a Nissan vehicle made after 99, the deforst automatically turns on the A/C. it does this to keep the side windows from fogging up.

heat doesn't suck any gas. it uses the engine's heat to warm the car. unless you have the windshield defroster running, in which case it turns on the A/C compressor so that does use gas.

tsk, tsk. Heat that comes through your vents is not off of the engine. it comes from a heater core(like a mini space heater) since it is electric it doesn't use any "engine power"

tsk tsk yourself. The heater core is filled with the same coolant from your radiator. It's not electric, that's why your heater doesn't work until the engine is warmed up.

 

[N8Magic]

Originally posted by: JeffreyLebowski
OK, if you own a Nissan vehicle made after 99, the deforst automatically turns on the A/C. it does this to keep the side windows from fogging up.

heat doesn't suck any gas. it uses the engine's heat to warm the car. unless you have the windshield defroster running, in which case it turns on the A/C compressor so that does use gas.

tsk, tsk. Heat that comes through your vents is not off of the engine. it comes from a heater core(like a mini space heater) since it is electric it doesn't use any "engine power"

Uh, the heater core isn't electric.

It has hot coolant flowing through it, which warms the air flowing over/through it and into the passenger compartment.

 

[mAdD INDIAN]

Originally posted by: Zenmervolt
The only gas heat uses is to run the fan. Heat blows air through a little radiator (the heater core) and then into the cabin. A/C has to run a compressor and all the ancillary items, plus the fans. Since the fans are electric, their impact is negligible and we really don't need to count them. The compressor runs off of a belt and takes around 5 hp IIRC.

ZV

EDIT: Defrost doesn't turn on the A/C on any of my family's car (Accord, Maxima, Explorer, 320i, and 924S). All defrost does is direct the hot air through the vents at the base of the windshield. The manuals say to turn the A/C on manually if the regular defrost isn't working well enough, but the A/C doesn't come on by itself with the defrost.

I was under the impression that the AC compressor would be used to humidify the air so the condensation would go away. Maybe I'm wrong..probably am since my old Corolla (aka God's Chariot) would defrost the front windshield and it did not have an A/C.

 

[Zenmervolt]

tsk, tsk. Heat that comes through your vents is not off of the engine. it comes from a heater core(like a mini space heater) since it is electric it doesn't use any "engine power"

You sir, are incorrect. The heater is not electric. A normal, liquid-cooled car's heater works by having a second, smaller, radiator called a "heater core". The coolant passes through the heater core before it goes through the radiator and after it has come through the engine, so the heater core gets the hot coolant as it comes out of the engine block. When you turn on the heater in the car, ducting forces a percentage of the incoming air through the heater core. The heater core is the same temperature all the time. The temperature of the air in the cabin is controlled by mixing the hot air from the heater core with some fresh air.

I don't know what kinds of cars you've been working on, but I have never seen an electric heater core on a liquid-cooled vehicle. It would be a waste of energy when there's all that free heat coming from the engine. Plus it would need an insane amount of amperage, turning on the heater would dim the lights if it were electric.

ZV

EDIT:

I was under the impression that the AC compressor would be used to humidify the air so the condensation would go away.

More humidity = more condensation. A/C dehumidifies. It can help defrost, but hot air still does best because it warms the glass to the point that condensation isn't possible any more, which also helps prevent exterior icing.

 

[justint]

MY 98 Hondas AC will turn on when you hit the Defrost. I believe that is default in most new cars.

 

[JeffreyLebowski]

Well i'm just blowing hot air around ain't I?

 

[Zenmervolt]

Originally posted by: justint
MY 98 Hondas AC will turn on when you hit the Defrost. I believe that is default in most new cars.

Ah, that may be why. The Maxima's a '98, and the Explorer's a '99. I guess neither was new enough to do that. After the Maxima, the newest car is the '88 Accord. (May the Accord rest in peace.)

ZV

 

[Scarpozzi]

Sometimes it's beneficial to run the A/C and the heater if you're cabin is getting all foggy. The compressor will take moisture out of the air and defrog your windshield quicker.

 

[0roo0roo]

i've always wondered this. figured recycled heat would be rather efficient indeed. wouldnt mind a few stats though.

 

[mAdD INDIAN]

I meant dehumidify...my mistake.

Yeah I was sure our 99 Maxima would turn on the AC compressor when the windshield defrost is activated. Cause you can see the tach needle jump a little when the button is pressed (much like the when the AC is activated).

maybe its cause the max has an auto climate control vs a regular one?


on a side note, readng up on auto climate control is quite interesting..didn't know it was so intricate

 

[KokomoGST]

Some older cars did use gasoline burning heaters... man, they got the car really nice and toasty... now, it takes forever to get my car warm... only way to get it warmer fast is to get on the boost lots.

 

[Evadman]

My mpg drops by aprox 15% when I use my A/C.