My newest lastest invention to save gasoline is very simple and although not probably patentable will save you gasoline in town in stop n go traffic where fuel economy is needed to improve the most.
Its easy, in a nut shell: Use a vacuum advance solenoid from an old style car (buy a new one at auto parts for $15, grab a 12 volt 1" x 1" x 1" cube relay that can handle 20 amps at 12 volts , some tubing, and wiring, two switches and an optional Led light, and you are in business, to turn off the AC compressor on start outs from stop lights, or passing, or going up hills, to give you a power boost when you need it, and also it by definition insures the ac compressor will be on when you are slowing down which helps save your brakes as well.
1. Install vacuum solenoid in a convenient out of the way place, run vacuum tube to convenient vacuum location on or about intake manifold.
2. Install momentary "on" type "trigger" switch on solenoid so that its "on" when the engine is running at idle (max vaccuum), this switch is connected to 12v (ignition switched on ) supply to its coil side, and provides power to the "relay" that you will install nearby.
3. Connect the primary wires of the 20amp@12v
relay to the AC compressor wires at the compressor (you will have to cut the negative compressor wire and connect the ends to the relay (also put in series about a 10 amp fuse for safety reasons in this wiring). Choose the relay terminal that is normally off (#87 terminal? ) so that when the "trigger switch" gives the coil power the relay and is powered on making term 87 pass the ground ac wire on thru to where it originally went.
4. The optional LED will sit on the dash and is supplied from a 12 v source such as the cigarette lighter and back thru the firewall to the negative relay primary ac wire connection (when the relay is powered on) to terminal 87 .
5. The other switch is an overide switch which allows you a way to completely bypass the whole gas saver circuit in the case where you are on the freeway going faster than about 40 mph (vaccuum is not so good the faster you go and you want the ac on for long trips or long hills etc). For this switch, take the wires going to the relay, tap into both wires , and run the new tapped wires to the switch, locate the switch in a convenient place on the dash (be sure to insulate and fuse everything you can very well so you don't have any shorting problems , even though its a negative ground connection to the ac compressor, we still would like to know that its well insulated).
Adjust the "trigger" switch so that its on when idling and off when accelerating, and on again when up to about 35mph, by sliding it back and forth along the vacuum solenoid arm that moves in symphony with the amount of vacuum from the intake manifold.
OPERATIONS: when in town, leave overide switch off, so that the vacuum will trigger the relay to turn off the ground connection to the ac compressor which gives you a boost of power as the compressor is not running,, about 3-5 HP boost (which is significant enough that you feel like you are being pushed back slightly in your seat)... this is for IN TOWN STOP n GO traffic situations in which the ac will be off for only about 3- 30 seconds at most..
FOR high speed or long up hills, turn on the overide switch and you force the ac back on, which costs you gasoline but also cools the inside of the car.
AGAIN most of our driving is in town in stop n go traffic.. so its a good idea.
Also "In Town", since the AC compressor is off, when starting out from lights and stop signs, it will come on more when you are slowing down (since it was just off for some seconds), which helps you slow down the engine saving your brakes slightly as well.
Est gas savings IN TOWN in stop n go traffic is about 5-10% when you realize that only 1 more mpg is 5%.