How to run a/c using less fuel? - Toyota Nation Forum : Toyota Car and Truck Forums

doozergreengrass · 12-30-2010, 07:59 PM

Don't know if the u.s versions of the 5sfe have climate control or not. However over here in oz (on our 93 and 95) they only have an a/c on/off switch. This really annoys me as I can see the mpg drop bad, and I hate the power loss. Is there any way to say give the compressor less fuel without causing any problems or is it just a complete waste of time. Seeing as our setup is mechanical (only on and off) as opposed to electrical (climate control sensing temp in car and therefore turning off when desired temp is reached), i'm assuming the heater control knob plays no part in the a/c department? Otherwise we have to keep manually switching our a/c on and off every few minutes to save fuel and that SUCKS!!!!

I guess what i'm saying is, when the a/c is run after awhile the car stars getting too cool, in which case we switch off the a/c. Then it starts to heat up again in the cabin and we repeat the process of off/on, very annoying.

Cheers

***LynchburgCSI*** · 12-30-2010, 08:25 PM

Uh. The A/C compressor clutch as two settings. Engaged and disengaged. The only way to control it is the A/C button on the dash. The green light comes on when you have the clutch engaged. It goes off when the clutch isn't engaged. Running the A/C saps power from the engine and hurts your fuel economy. Nothing you can really do to help it except turn the A/C off. Simple as that.

typesix · 12-30-2010, 08:32 PM

Only other thing to do is use the recirc air position instead of fresh air position to save on fuel, so that cooling coil won't see hot outside air.

Yuko · 12-30-2010, 08:38 PM

With the A/C button on, you should be able to adjust how often the compressor runs with the temperature switch/knob. The compressor shouldn’t run 100% unless the A/C is set to full.

The compressor runs depends on load and setting. Sadly, our cars have the older on/off compressor. When load is light, the compressor clicks on and off, then on and off. (different from low freon) When load is high, the compressor will run nearly continuously. Newer variable compressors have a swash plate to adjust the load. It runs smoother and claimed to last longer. When load is light, the angle of the swash plate inside is backed off to pump low amount of refrigerant. When load is high, the angle is increased to pump more refrigerant. No clicking on and off unless the a/c button is off but more new car will run the compressor if the defroster is turn on.

***N/A Camry Sleeper*** · 12-30-2010, 08:49 PM

Quote:

Originally Posted by doozergreengrass

Don't know if the u.s versions of the 5sfe have climate control or not. However over here in oz (on our 93 and 95) they only have an a/c on/off switch. This really annoys me as I can see the mpg drop bad, and I hate the power loss. Is there any way to say give the compressor less fuel without causing any problems or is it just a complete waste of time. Seeing as our setup is mechanical (only on and off) as opposed to electrical (climate control sensing temp in car and therefore turning off when desired temp is reached), i'm assuming the heater control knob plays no part in the a/c department? Otherwise we have to keep manually switching our a/c on and off every few minutes to save fuel and that SUCKS!!!!

I guess what i'm saying is, when the a/c is run after awhile the car stars getting too cool, in which case we switch off the a/c. Then it starts to heat up again in the cabin and we repeat the process of off/on, very annoying.

Cheers

Ah - must be summertime down there!

Back in July I had the same problem with my Camry - the crappy mileage with no way to "economize" the A/C system. Unfortunately there's no remedy I know of except manually switching the compressor on and off - I also know the difference in gas mileage and power is like night and day with the 5SFE. Only thing I can recommend is to engage the compressor while coasting down a hill and vice versa while going uphill. If you live in a flat area, well, there's nothing really to do. Making sure the condenser coils are clear and bug free will help a little as well. I would imagine that using A/C coil cleaner (which is basically diluted oven cleaner) on the condenser will help a little as well but never got that far with mine.

Hope this helps!!! I know the frustration!

***fenixus*** · 12-30-2010, 09:41 PM

yeah, manual HVAC controls and a/c on/off button ... have got the same crap on wife's '00 Solara 2.2L. nothing really you can do except for turning it off when you going uphill or want to accelerate faster (without crazy high RPMs).

as far as I know turning the heater knob up will only eventually engage heated air together with the cool (dehumidified) air, so no point in that... that is in Summer

doozergreengrass · 12-31-2010, 02:29 AM

Thanks everyone......yeah summer down here (40oC today!!!) ah well don't have to drink as much when its hot haha. So there's no way like of say changing the fuel delivery pipe to the a/c (i don't actually know where the fuel for the a/c goes, compressor or somehwhere else?) so it gets less fuel or something? I know this question sounds stupid to some, but thats all I can think of - but I doubt the onboard comp. would like such unauthorised changes to its little world of thought!!!!!

Happy new years everyone from Oz/New Zealand.....be safe - and be good (or be good at it....)

***BMR*** · 12-31-2010, 01:17 PM

Quote:

Originally Posted by doozergreengrass

So there's no way like of say changing the fuel delivery pipe to the a/c (i don't actually know where the fuel for the a/c goes, compressor or somehwhere else?) so it gets less fuel or something? I know this question sounds stupid to some, but thats all I can think of - but I doubt the onboard comp. would like such unauthorised changes to its little world of thought!!!!!

The AC system doesn't have its own fuel supply. The AC compressor is driven by a belt which is powered by the engine. The compressor has a magnetic clutch which engages/disengages the compressor as needed. So it's either on or off.

***Mister_Perkins*** · 12-31-2010, 01:21 PM

get an electric A/C Compressor. Problem solved

deadrx7conv · 12-31-2010, 02:11 PM

Electric AC compressor would just draw on your alternator. The load increase would be similar to the compressor kicking on.

As mentioned, use the recirculate button. This should help to keep the inside comfortable.

And, make sure your AC is completely charged up properly. I find the biggest problem is excessive compressor load due to not enough refrigerant. It might be time for an evac and refill, with the correct refrigerant/oil charge.
Since 134a isn't the best refrigerant, some 134a's are blended with a chill-kicker, freeze-booster, or with a ratio of another refrigerant that improves 134's performance.

There was a time when underdrive pulleys were more available. In the cars that I've used them in, the MPG loss with the AC on was definitely less.

Another option is to sweat it out. Its not all that hot out.

If humidity is very low, evaporative mist cooling is an option. Not recommended in humid environments because it adds humidity and you're already sweaty sticky.

doozergreengrass · 01-07-2011, 07:07 PM

Quote:

the AC system doesn't have its own fuel supply. The AC compressor is driven by a belt which is powered by the engine. The compressor has a magnetic clutch which engages/disengages the compressor as needed. So it's either on or off.

I'm a little confused here! So does the a/c run just by engaging/disengaging its clutch? If its not running off fuel why does the power drop when the clutch is engaged? Its not running off electricity right otherwise why would a electric compressor be recommended?

I know the belt from the crank shaft turns the a/c compressor (and alternator), are previous posters basically saying that the compressor is so hard to drive/turn with the clutch engaged it saps power from the crank shaft?!

***LynchburgCSI*** · 01-07-2011, 07:12 PM

Quote:

Originally Posted by doozergreengrass

I'm a little confused here! So does the a/c run just by engaging/disengaging its clutch? If its not running off fuel why does the power drop when the clutch is engaged? Its not running off electricity right otherwise why would a electric compressor be recommended?

I know the belt from the crank shaft turns the a/c compressor (and alternator), are previous posters basically saying that the compressor is so hard to drive/turn with the clutch engaged it saps power from the crank shaft?!

^ yep! That's why you lose power. Engine power, not electrical power. Well, unless the strain causes the belt to rotate marginally slower and thus have the alternator spin slightly slower.

I was 95% sure the A/C compressors on these cars we're strictly ON/OFF. Someone correct me if i'm wrong.

doozergreengrass · 01-07-2011, 07:22 PM

Thats why i'm confused, does dialling the heat up a bit run the compressor less? Or just mix warm air into the cabin? If so how does it know to do so from the temp knob???!!!!

Quote:

With the A/C button on, you should be able to adjust how often the compressor runs with the temperature switch/knob. The compressor shouldn’t run 100% unless the A/C is set to full.

Can the clutch be adjusted inside the compressor to only engage halfway?

deadrx7conv · 01-07-2011, 07:33 PM

No, a clutch can't be adjusted to go half-way.

I find that the AC cycling frequency isn't too variable. Playing with the dash temp lever is meaningless. It'll still cycle just as often. All it does is add in heat from the heater core.

***LynchburgCSI*** · 01-07-2011, 07:40 PM

^ And by cycle, he means the clutch automatically being engaged for a while, then being disengaged for a while.