lowering a/c dial saves gas?

jkandell · #1 08-24-2007, 08:31 AM

Does lowering the dial on the a/c (so more warm air gets mixed in) raise mpg?

johnf514 · #2 08-24-2007, 08:38 AM

Absolutely - the compressor runs less, therefore robbing less engine power and fuel.

psyshack · #3 08-24-2007, 08:40 AM

Quote:

Originally Posted by jkandell

Does lowering the dial on the a/c (so more warm air gets mixed in) raise mpg?

Nope,,, all your doing is mixing in warm air from the heater core. Slowing down the fan doesn't help either. Now if you have auto climate control. You might beable to set a temp and have the compressor kick off once temp is met. It all depends on how the system is built.

laurieaw · #4 08-24-2007, 08:40 AM

definitely! on my HCH the dial reads in degrees, 62, 72, 82. when i put it just before the heat comes on, it does a fine job of cooling and taking humidity out of the car. setting it to 72 gives me frostbite, which i can get in the winter for free

johnf514 · #5 08-24-2007, 08:52 AM

You sure about that, psyshack? In every car I've owned, I can feel the AC compressor staying off for longer periods of time when the temperature gauge is on a warmer setting.

2007 Mz3
1999 Taurus
1999 Camaro
1989 Voyager

brick · #6 08-24-2007, 08:55 AM

Psyshack hit it square-on: it depends on how the system is built. In order to see any benefits with the Accord (not automatic climate control) I had to manually turn off the A/C compressor. The knob was just an air mix that changed temperature at the vent. The Prius, on the other hand, uses an automatic system with a variable-speed compressor that only sucks enough power to meet demand. Increasing the temperature setting reduces the influx of heat to the cabin by virtue of a lower temp gradient which, in turn, makes it easier on the climate control system.

If you have automatic climate control you should be in good shape.

johnf514 · #7 08-24-2007, 08:59 AM

I must be off my mark then - none of my vehicles had climate control.

Consider my posts null and void.

laurieaw · #8 08-24-2007, 09:57 AM

sorry, i guess i should have added mine does have an automatic setting, which i haven't really used much since i don't put the a/c on very often. that said, i did see a difference in how it ran based on the temp setting.

Dan · #9 08-24-2007, 10:27 AM

Quote:

Originally Posted by brick

...The Prius, on the other hand, uses an automatic system with a variable-speed compressor that only sucks enough power to meet demand. Increasing the temperature setting reduces the influx of heat to the cabin by virtue of a lower temp gradient which, in turn, makes it easier on the climate control system.

Sweet, thanks for the insight.

11011011

brucepick · #10 08-24-2007, 10:27 AM

My view on it is that you should feel or hear the compressor starting and stopping (unless it's a variable-speed compressor as above). In the a/c cars we've had in the past, we also could feel the difference in vent air temperature right after it started or stopped. You can use these observations to detect how your system is programmed.

I would think that the various makers, and various generations of systems over time, will have different names and setups. But if you can hear or feel it cycling on and off more or less often, that would tell you what's going on.

Quite likely many service techs will not know the answer to the question as their job is to fix it when it's broke, usually a matter of sealing leaks and adding refrigerant.