It's that time - our fuel is changing. I've had a theory for a while and I'm going to put it to the test:

Did you know that any time you turn the vent select **** to the right that it activates the AC compressor? I could be wrong, but I think that one piece of hardware uses about 5 HP to operate. I read a number one time - stating it takes about 60 HP to keep our trucks at highway speed (60-65 MPH) on the flat with no wind. If I add that 5HP load when I want warm feet, that's close to a 10% hit on my fuel economy. I pulled the plug on my AC compressor to run this test and see what happens.

Caveats: It's best to cycle the compressor on a regular basis to keep it functioning properly, so this will be temporary. The AC also helps to warm the truck quicker and put warmer air in the nose.

If I'm going to do something like this permanently... I'd put a switch on the AC to kill it when desired, and I'd want a grille cover for those really cold days without the AC running.

OK brothers... I'm ready for the arrows to poke holes in my theories here. Bring it!

 

Ive always noticed my ac conpressor ran on the split level function and thought it was abnormal. I wonder if the selector can be modded so it doesn't cycle the compressor on that setting. I've never wished for split level ac, however I always use it with heat. Good catch though. One point to add, on my 89 and my corvette on days below 30 the compressor wouldn't even run. I wonder if the same holds true on these trucks?

 

Keep in mind one of the functions of the compressor running is to dry out the air, hence the defrost/defog effect.
But this is a good experiment, and your the one to do it right Rich.

 

The A/C also helps to dry out the air in the cabin, reducing humidity build up on the windshield.

Not much of a problem in Tugly's neck of the woods. But it's uber important in the Pacific Northwet... I mean Northwest.

(Dang it. Trekbasso beat me to it.)

 

I now live in northern Colorado, but being from Houston I am well versed in humidity.

 

All sounds good to me - I dislike the fact that Ford didn't provide a separate A/C switch on the F series. I agree that you should cycle the compressor 1x/mo or so to keep the system oiled internally. As others mentioned, it shouldn' run below 30-ish F, due to icing concerns.

 

So how will you actually track the change? Time frame, miles? Results may be difficult to interpret if variables are completely random, thus a lengthy time frame or a good numbers of miles may be necessary to see reproducible result. Also would you not first need to leave the plug alone and establish a baseline, before disconnecting the plug, unless you have already done so. Just wondering

Steve

 

I get better fuel mileage during the summer than during the winter. I think the winter blend has something to do with that. Cleatus says it's likely due to the fact that a lot of us start our truck and let it idle in the driveway while we get ready for our day....that theory makes a lot of sense to me.

Where I live we use the A/C 100% of the time from mid April to mid November. I see zero effect on MPG whether the A/C is used or not. I don't use the A/C at all during the winter since I never use the bi-level setting on my truck. I can't stand warm air hitting my face....

 

It will indeed be a difficult theory to test with so many variables. I also never run bi-level for the same reason.

Steve

 

The A/C compressor should not turn on in the FLOOR position. Here are the pages from the service manual that explains the operation for each switch position. I included both 1999 and 2000 since the operation is slightly different between the two years...

 

I've been tracking my mileage and I have a long-haul coming, where I usually have the heat on with winter-blend fuel. It will probably be inconclusive (no real difference), but it doesn't cost anything to try.

 

That is odd. Something may be wrong with your system then....

 

completely normal operation in my truck. The bi-level indeed will chill my feet/face, during the summer. Heck, i never switch to A/C or MAX, because the ni setting is cold enough...i wonder if the Ranger Mod had anything to do with this/that?

 

My trucks stays on bi-level all winter long. I hate that hot air hitting my face as well. Although I also hate the dry air from the defroster bouncing off the windshield and hitting my eyes first thing in the morning too.

 

You caught me mid-edit. I have not confirmed anything with feet-only, I just know three of the four settings are confirmed.