So do a lot of other underpowered cars, like new Corvettes. I think it's pretty common.
Recirculated Air Saves Gas?
- Thread starter Jonny Z
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My Toyota cycles the compressor and it cycles much less with the air on recirculate.
Most cars will cycle the compressor less on recirc to keep the evaporator coil from freezing up. If the temperature of the incoming air is lower, that means the evaporator coil is more likely to freeze up so it will cycle the compressor less to prevent that.
There's actually a pressure switch that does this, and I believe it cuts off once the pressure drops below a certain value. The lower the evaporator coil temperature, the less the pressure.
By the way, if you're too cold, instead of turning the temperature knob up, turn the fan to a lower speed. That will cycle the compressor less.
There's actually a pressure switch that does this, and I believe it cuts off once the pressure drops below a certain value. The lower the evaporator coil temperature, the less the pressure.
By the way, if you're too cold, instead of turning the temperature knob up, turn the fan to a lower speed. That will cycle the compressor less.
I hadn't thought of potential efficiency gains from the re-circulate button. I'm going to do some temperature checks because I perceive there to be a temperature difference between the cooled air when it's on re-circulate versus fresh. Of course, there's also an odor that I find unpleasant in every car I've ever ridden in when the air is constantly re-circulated (no, it's not just me smelling things up... all the time).
If you have a thermostat in your car that you can set the desired temperature with, you will save fuel with the MAX setting. Cooling cool air is better then cooling hot air.
Most sytems that are on/off will see no difference in economy. The compressor is running/cycling either way.
Using MAX will keep moisture in the car, and can be uncomfortable and fog windows. It is good to quickly get the interior temps. down, then you can switch to the normal outside air setting.
Most sytems that are on/off will see no difference in economy. The compressor is running/cycling either way.
Using MAX will keep moisture in the car, and can be uncomfortable and fog windows. It is good to quickly get the interior temps. down, then you can switch to the normal outside air setting.
Of course however a little sweating of the evap coil doesn't hurt the system and helps prevent coil freeze up in some systems.
When I first take off on a hot day I set the AC to it's coldest setting and put it on recirc to remove the excessive humidity in the car.After a while if the settings are still the same and it feels like it's not cooling anymore I put on the outside air for a minute and then back on recirc to reintroduce some humidity.
If after a while, your A/C feels like it's 'not cooling anymore', introducing humidity wouldn't be an improvement. Would you open all the doors and windows in your house if your A/C seemed to stop cooling?
This sounds like a temperature switch problem. Any car I've ever owned continued to cool the air until it got too cold, at which time I had to turn it down, or off. You might want to have that looked at.
This sounds like a temperature switch problem. Any car I've ever owned continued to cool the air until it got too cold, at which time I had to turn it down, or off. You might want to have that looked at.
You can try an experiment. While driving down the road, turn you a/c on, to circulate throught the cabin, and on recycle. Now, reset it to defrost the windows, and watch the recycle light go out. That makes Alan's statement true, if it happens in your car, too. Don't trust Alan, experiment, Alan could be trying to pull a fast one on you. After all, you must never trust an Engineer.
The reason that defrost pulls in outside air is because of winter.
In winter, the air inside the car is likely to be much more humid than the air outside the car. If defrost didn't pull outside air in, it wouldn't work very well and the windows would continue to steam up. (It would be too cold outside for the AC to work, so no dehumidification would take place). You can see this effect on cars that don't automatically turn off recirculate when you select defrost.
In summer, it makes no real difference that I've seen, and in fact when it is raining out and I am getting condensation on the windows, I turn on MAX AC (aka recirc) for the energy savings and that does a fine job of clearing it off, although sometimes I do have to turn it on DEFROST for a couple of seconds to get the process started simply because MAX AC doesn't blow out of the defroster outlets.
Coil freeze up? That doesn't happen on properly designed, properly charged AC systems, regardless of humidity. Now if you're using a residential central AC system to cool your data center in winter, then yes, coil freeze up is a problem but there is a fix.
My understanding is that most car AC systems are set up to keep the evaporator coil temperature just above freezing. Given that, I fail to understand how introducing humidity would either prevent coil freeze-up or increase cooling. It doesn't for home AC units--it in fact decreases cooling on those. Car units I expect would be the same.
In winter, the air inside the car is likely to be much more humid than the air outside the car. If defrost didn't pull outside air in, it wouldn't work very well and the windows would continue to steam up. (It would be too cold outside for the AC to work, so no dehumidification would take place). You can see this effect on cars that don't automatically turn off recirculate when you select defrost.
In summer, it makes no real difference that I've seen, and in fact when it is raining out and I am getting condensation on the windows, I turn on MAX AC (aka recirc) for the energy savings and that does a fine job of clearing it off, although sometimes I do have to turn it on DEFROST for a couple of seconds to get the process started simply because MAX AC doesn't blow out of the defroster outlets.
Coil freeze up? That doesn't happen on properly designed, properly charged AC systems, regardless of humidity. Now if you're using a residential central AC system to cool your data center in winter, then yes, coil freeze up is a problem but there is a fix.
My understanding is that most car AC systems are set up to keep the evaporator coil temperature just above freezing. Given that, I fail to understand how introducing humidity would either prevent coil freeze-up or increase cooling. It doesn't for home AC units--it in fact decreases cooling on those. Car units I expect would be the same.
You must be experiencing some moisture condensation on your face / body when you do this, and the conditioned air in your car is cooling your skin. The introduction of humidity to an A/C system does not increase it's effectiveness. The A/C's job is to remove moisture from the air, so you're just making its job harder.
The two cavaliers I have owned were opposite of what some are saying. When switching to defrost, the AC would turn on and it would switch to recirculating air. I always thought that made the most sense, too. But my new mazda6, otoh, is the opposite.
What if I posted that my air-conditioned temperature readings show that the air temperature coming out the vents of my car are lower with the air selector set to fresh air, and higher when set to recirculate? All under the exact same conditions, of course: Driving down the freeway at ~60 mph.
EDITED to add the word 'air-conditioned' for the sake of clarity.
[ June 27, 2006, 12:14 PM: Message edited by: bulwnkl ]
EDITED to add the word 'air-conditioned' for the sake of clarity.
[ June 27, 2006, 12:14 PM: Message edited by: bulwnkl ]
1. I don't have my wind gauge at hand, but this one seems apparent from just putting my hand in front of the vents.
2. Surely possible.
An implication of the above is that it may NOT be more fuel efficient in real life to run the A/C on recirculate if the the air blowing out the vents provides the same amount of 'cooling' to the cabin/passengers either way (lower-volume, cooler air vs. higher-volume, warmer air may be equivalent cooling-wise).
[ June 27, 2006, 03:41 PM: Message edited by: bulwnkl ]
2. Surely possible.
An implication of the above is that it may NOT be more fuel efficient in real life to run the A/C on recirculate if the the air blowing out the vents provides the same amount of 'cooling' to the cabin/passengers either way (lower-volume, cooler air vs. higher-volume, warmer air may be equivalent cooling-wise).
[ June 27, 2006, 03:41 PM: Message edited by: bulwnkl ]
I invite you to do that
Hot, humid outside air passing over the evaporator and into the cockpit will not be cooler and drier than air that's already been conditioned. It's simple logic. If your A/C is blowing cooler air on fresh than it is on recirc, there's a problem with your under-dash venting.
Go to a dealership and tell them your A/C isn't blowing very cold. I guarantee the first thing out of your service advisor's mouth will be "are you running it on recirc?". It's in the owner's manual, and it's what service departments advise.
Go to a dealership and tell them your A/C isn't blowing very cold. I guarantee the first thing out of your service advisor's mouth will be "are you running it on recirc?". It's in the owner's manual, and it's what service departments advise.
When simple logic is contradicted by observed fact, something may need to be reevaluated.
I did not say anything about humidity. Can you think of a simple reason for a temperature difference between fresh and recirculate? I can think of a very simple one (though it may or may not be correct or the only factor). BTW, the A/C system on the vehicle I'm measuring at present was recently evacuated and recharged when a hose was replaced. For the sake of curiosity I would like to also measure the temps on our other vehicle.
I did not say anything about humidity. Can you think of a simple reason for a temperature difference between fresh and recirculate? I can think of a very simple one (though it may or may not be correct or the only factor). BTW, the A/C system on the vehicle I'm measuring at present was recently evacuated and recharged when a hose was replaced. For the sake of curiosity I would like to also measure the temps on our other vehicle.
1. Possibly from a higher airflow rate on recirculate.
2. Possibly from more heater air bleeding into the airstream on recirculate.
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