Keep A/C from running when you don't need it.
 

Hello.

I'm new here but wanted my first post to be useful. :)
So I'm putting it here.
Now I don't consider myself to be quite as dedicated as some of you.
I come more from the "more power" camp, but do want to always get the most MPG as well. (Tesla anyone?)
But I have been popping in and looking around from time to time and have come away with more ideas and respect for those trying to get the most out of the machine they have.

Anyway.
This is for those who still want to keep the A/C installed for those days they just can't do without it. But don't want it cutting into the quest for better MPG when they don't want it.

Some may know that most modern cars that have A/C equipped, actually turn it on when you switch the windshield defroster on. This is to dry the air to speed up the defrosting.
But this is also cutting into the MPG in the winter while all you want is the defrost, but get the A/C in the deal as well.

So this is what I did.
*I own a 2005 Ford Focus. (best MPG has been 37 and I was not always being "gentle" on a x-country trip) I also did this to my 2002 Focus.
This may be different depending on the vehicle, but I hope to point some in the right direction.

So I noticed when I turned the selector knob to defrost that the compressor kicked on. This had me right away looking for the cause. I know it's normal, but I didn't want it to work that way.
So I took apart the dash to get at the back of my selector knob. (this was a week old car keep in mind :D )
What I found was a wire plugged into a switch on the back of it.
I simply unplugged it.
That's it.
No more A/C compressor running all winter unless I hit the A/C switch.
for me it meant smoother running, more "oomph", and better MPG.
The selector knob I speak of is the one that you use to select wher the air blows, vent/floor/defrost/ect.

Like I said it may be slightly different on other cars. So you'll have to consult a wiring diagram or just poke around. But the basic principle will be the same.
To keep that pesky A/C compressor fully under YOUR control. ;)

LOL - The van I have now is the first one that's actually new enough to have that sort of feature, and I don't believe it does, but I'll have to double check some day.

On my older manual cars which had A/C, I put a switch at the top of the gas pedal, so that when I let off it, the A/C pump would kick on (if the actual A/C switch was on). But any time I was on the gas pedal, it wouldn't kick on at all.

This setup was great, because the only time the A/C pump would work was when the engine was in fuel cut mode... so the A/C wasn't wasting any gas at all!

And, of course, welcome to the forums! Enjoy your stay!

My buddy's '91 F-250 deisel has it too.
Wonder if it was mainly a Ford thing except on newer vehicles?......

My car is a little too new for me and the HVAC console is totally digital. No knobs, just a few buttons and an LCD screen. Yes, the A/C light comes on when defrosting, but good luck to anyone who can hack into it.

the biggest killer of A/C is letting them sit for months without running them, that is why some cars the A/C kicks in for just a moment every time you start the car, others it kicks in with the defrost (something you can turn off with alot of cars, but only after it's turned it's self on) sure this drys the air but it also saves the environment by keeping the pump seals from drying out.

So if the A/C shouldn't be left off for months, then defrost is the only way to turn it on every once in a while. Some cars (like mine) don't turn on the A/C below a certain outdoor temperture, even if it's warm inside. Now I get it. Thanks Ryland :)

Hi,

I unplugged the A/C fuse over the winter, and it paid dividends on every icy drive -- I needed all the heat the car could muster, and the LOWEST mileage I got all winter was 41mpg.

I'm thinking back to the heady days of the Hyundai Excel, whose AC was welcome in our balmy, sticky summers but I still had to turn off when approaching hills if I wanted to top them before lunchtime...

Did I mention I live in the foothills of the Appalachians? It's nothing but hills around here. And do I miss said Hyundai, and its tiny no-guts engine? Oh, no.

All A/C systems have some form of low-pressure shutoff switch to protect the compressor from fluid lockup. If your evaporator "freezes up" the compressor needs to shut off to keep from continually icing it which will cause high-pressure liquid to back up into the compressor on the high pressure side by evacuating the low-pressure side through the compressor running when it isn't needed (the super-cold evaporator will cool the air without refrigerant running through it while it thaws).

Locate the low-pressure shutoff switch. Figure out what you have to do to force the compressor off; in my old truck removing the connector leaving the switch circuit open forced the A/C off while jumpering the switch terminals with a wire forced the A/C on. If this is the case splice into the wire (or one of the wires) with a manual toggle switch you can mount under your dash.

The switch will be located on somewhere between where the evaporator tube passes through the firewall and the compressor (not in the run that includes the condensor, the other half of the circuit). It will probably be closer to the firewall rather than near the compressor.

My Mom had an Excel in the late '80's. The A/C was off on even the smallest hill. I remember a trip to Grandfather Mountain in NC. At some point not too far up the car cried "NO!!!" and the rest was on foot. In retrospect maybe that was a good thing, but I always wonder how my Mom is still sane after having to pull a young kid up that mountain...