Or just put a vacuum gauge on the engine.

 

I don't think one trip is sufficient information to make a call yet. Call us in 6 weeks again, and give us the MPG's with the setting on "vent".
I start out every morning with defrost for about 5 minutes., after that, I leave the setting on vent or floor heat. If further "defrost is required, you are...1 Driving on a very humid rainy day...or 2 the truck cabin has a a leak and something is damp..like your rug.

 

Agree with prev post, one trip isn't enough to draw the conclusion that the ac on with defrost is worth 2 mpg.....

And fyi, its a Federal Motor Vehicle regulation from the mid '70s requiring better performance from defrosters.

Metalized glass is probably the better solution, but I'm not sure anyone is still doing this. GM did it on the Olds minivan, but I think the ac was still used for the defrost. Sent that baby down the road so I can't run out and check.

 

I've got a 93 regular cab long bed 4x4 302/auto and have to make a 230 mile trip home and back from college every once in awhile and twice i used the defrost going home and got 13mpg. Coming back to college i got 17 both times without using the defrost. (Switch was set to off). Dont know exactly why this happens, roads were dry, wasn't very windy either way?

 

I certainly don't know what the weather is like in the great states of OH and PA during the winter months, but here in Washington, "defrost" IS required pretty much full time to keep the precipitation from freezing to the windshield...

And I can agree that 150 measily miles is NOT enough to call anything certain. It was merely an observation and a question that came to mind based on what I saw...

 

O.K.

just telling you after windshield defrosts i don't need it on.

 

It make a 1.5mpg in my 96 with a 302! thats why i've got the wire pulled. Why didn't ford just put a button on the dash like everyone else? Use the A/C to help then shut it off and leave the **** on defrost.

44

 

I agree. They used to on at least some vehicles through the 80's. I may add a switch myself to solve that problem.

 

That would be some good tech... Depending on the actual results, it would probably even be worthy of a sticky at the top of the forums?

 

So just to get things straight, its OK to pull the plug off the compressor? Mine doesnt work anyway, it just makes an annoying sound every so often with the defrost on.

 

Just my $0.02, I've not noticed any difference with the AC on or off in any of my vehicles. I'd agree with Fmr2. I'd also agree with 924X2140 though. I think you need to try that test a few more times to be sure. I'd disagree with the comments about how the AC shouldn't run in the defrost setting though. The AC makes a big difference in humid weather in keeping the windows defogged, espcially in the fall when the temperatures are in the low 40s and and it's humid outside. For a brief period of time, I had two Ford Tempos, one with AC and one without. The Defog setting in the one with AC worked much faster than the one without. As far as older vehicles go, even they ran the AC with the Defog swith on. I drove a '78 Volare for awhile and it's AC ran in when you pushed the Defog button, and I'd assume that 76es and 77s were the same.

 

You could pull it off the compressor. Mine has a low pressure switch at the acumulator. I've unplugged mine there and it's fine. I think at the compressor would give more chance of the connector getting into a belt or pulley. Just my .02

 

Anyone got an idea of the Amps the compressor draws on start-up? I'd like to try splicing in a toggle switch, just for grins...

 

I just unplugged my compressor under the hood and I dont have any problems with it now. In the summer when I want A/C (wich is vary rare in MI) I just plug it back in.

 

The compressor clutch can't pull many amps, judging by the size of the wire used. A switch on the dash is a better idea than unplugging it. It is better to run occassionaly to keep the seals lubed.
Frank