hey fellas,

just having an arguement with my FIL about the defroster running off, or using A/C components while the defroster is in use. he's saying that the heat has nothing to do with the A/C regardless of weather its on defrost or panel/floor/etc... can someone simply explain if i'm right (saying the 2 are directly related) or out to lunch that the defrost has nothing to do with the A/C equipment??

truck in arguement is my '02 s'crew XLT...

thanks

 

I belive when the defrost is on the ac compressor kicks in also whether the temp control is turned to cold or hot

 

The A/C runs when the defroster is on because it dries the air and will defog the windshield waaay better, including when you have the heat control turned up (for hot and dry air, which is what you need in the winter).

If you get into your truck or car sopping wet from the rain, you can turn the heat control to either defrost or the A/C position, crank the fan, and crank the heat up if it's cold out, and note how much quicker your jacket and hair will dry.

A home dehumidifier works by pulling air through cold coils, on which water condenses like on a glass full of ice water. Every home air conditioning unit pulls water out of the air.

I believe that the car A/C may not run below certain temp thresholds, like below 32 degrees, but if you want to see what's going on, open your hood, turn on the defroster, and note that the A/C clutch is on and the compressor is spinning. Show your FIL....some folks have this strange idea that the only way to run the A/C in a car is with the temp all the way on cold so you're freezing, but the idea is to use the A/C along with the temp control to be comfortable...and dry.

George

 

thanks a whole pile George and mudbuggy. i understand now...i was right

 

If your FIL is also in Sask & he's talking about how it works during winter, he's pretty much on top of it. DEF stands for 2 things DEFrost & DEFog. According to FORD the AC compressor will only run above ~50 degrees F (10 C).

When used in winter as a DEFroster the AC is never supposed to run. In warmer weather, above 50 where DEFrosting is never required, the AC will run, regardless of TEMP setting, to dehumidify air & greatly increase DEFogging capacity.

 

i believe that it runs at a lot colder temps than that. i've heard
seen it cut in when i switch the dial to DEFrost... there is an audible change in engine tone, and its easy to see a slight decrease in MPG when its used just as the A/C in the summertime.

 

Of course you're free to "believe" whatever you like & there is the possibility that your pickup does not function as it was designed.

I was not stating my opinion, my post was based on info directly from a FORD F150 owners manual. If you need to DEFrost your windscreen & your AC is running, the system is acting to defeat your goal.

Below ~50 F the AC compressor should not run in DEF mode, according to what FORD believes.

IMO your FIL was correct as you presented the general argument. I didn't attempt to account for irregularities of your particular vehicle, only the way FORD designed it. Perhaps your low temp limit switch is "out to lunch"?

 

For the record, my '02 Econoline manual indicates that the A/C operates above 43 degrees F, and based on where the temperature sensor is, I'm guessing that engine heat also plays a part in the reading. I have had other cars that I recall as using a 32 degree threshold. It was 28 out today and my Protege5 hit the A/C in defrost mode.

And my reading of the original argument is that FIL said "heat has NOTHING to do with the A/C" (did you actually read the post?), which I interpret as entirely wrong, as the A/C evaporator and heater core are in the same path and are completely related, as on a vehicle with climate control.

There are a couple older gentlemen I know, including my late stepdad (bless his soul), who never understood that you could turn the heat **** up when you ran the A/C--thinking it had to be full cold or something, which froze my late mom big time, so he was usually forbidden from using the A/C when she was in the car 8-) I think this dates back to when A/C units hung under the dash and were standalone recirc only units.

You seem so concerned about being precisely correct that you're possibly missing the actual question.

 

X2, Right on.

 

Lets try to keep this within the '1997-2003 F150' section. Besides there is still no frost to be DEFrosted even at "43 degrees F" in your Econoline. Let's agree to leave your "Protege5" out of it?

I "actually read" & interpreted the post just fine. How do you interpret "just having an arguement with my FIL about the defroster running off, or using A/C components while the defroster is in use."? Cite Econoline info & the fact that AC evaporator & heater core occupy the same housing? The issue has to do with when the AC compressor should run. A passive evaporator contributes nothing, it requires liquified refrigerant to perform it's function.

The fact remains that the AC compressor should never run at the freezing temps that are associated w/DEFrosting. I clearly stated the AC's proper use in DEFogging at higher temps.

I'm an older gentleman who remembers AC's that had thermostatic temp control that cycled the compressor to achieve desired temp, instead of the F150 bi-level system.

If I was interested in being "precisely correct" in this instance, I'd tackle the common error related to "he's saying that the heat has nothing to do with the A/C regardless of weather its on defrost or panel/floor/etc...". FTE posts have shown that many seem to be mystified by the control. Heat, if selected, can have something to do with A/C in every position except OFF and FLOOR or PANEL, which are the 100% heat or fresh air selections. The PANEL & FLOOR position is the main bi-level position. To save gas by cutting out the compressor, FLOOR or PANEL positions should be used. I would presume that in Sask its been months since its been warm enough for the AC to run, it should essentially hibernate all winter.

While "the A/C evaporator and heater core are in the same path and are completely related" physically, you seem to be "possibly missing" the critical functional difference. The A/C evaporator only functions when the compressor runs, whereas the heater core circulates hot coolant whenever the motor runs.

I don't know how much clearer I can state this. When trying to remove ice/frost from WS where "the defroster is in use" you DO NOT want the AC compressor running. 96sherm & his FIL's argument did not mention DEFogging as presented here.

 

...so I think that's where we should leave it. My semantic error is calling the "defogger/defroster" simply the "defroster", which, as an old guy, is just something I do when I put the rotary **** on the little windshield symbol. Maybe FIL does the same....

And even when it's below freezing, I've had fog on my windshield, and know that at least part of the time, the A/C has been running to help remove that moisture. Although the implication is that the vehicle knows exactly what the outside temp is, the sensor is somewhere on the vehicle, probably near the engine and/or radiator, and is probably not *perfectly calibrated*. Cars with outside air thermometers in them usually read much warmer than the outside air temp when restarted after a short time, until they are driven. Had a number of these, all of them are the same. I'd bet that under the same circumstances, or standing in rush hour traffic with a hot engine with the outside temp below freezing, the sensor is not reading the real outside temp but has some bleed-off of warm air thru the grille.

Again, we agree, so let's have an excellent evening, shall we?

George

 

so basically, the DEFROST system does somewhat use the A/C equipment?? or it doesn't use it at all??? simple answer this time, no peeing contest... i know i've heard/felt/seen it cut it, but whatever... have a good one all, thanks for your replies.

on edit, i'm calling the defrost and defog the same freaking thing too. same pooh, different pile. its clearing moisture off the windows.

 

Hence the *~* in the "~50 degrees F" limit I posted from FORD.

All inaccuracies considered, Sasketchewan has 5 solid months when it rarely gets over freezing, consistantly far below FORD's ~50 F spec. The F150 AC system should cut the compressor out by this low temp limit. Under those cold conditions FORD's design means "the heat has nothing to do with the A/C" & "defrost has nothing to do with the A/C equipment" b/c the compressor should be switched off. When the compressor is switched off the A/C system is no more functionally "related" to cab air distribution than the spare tire.

If 96sherm's pickup has it's A/C compressor running, at any control position, in those cold temps, there is a problem. IMO the FIL was right, the A/C shouldn't run at all & has no bearing on air distribution, until it gets considerably warmer. Until then its just along for the ride.

Excellent evening to be sure. Just had a delicious, fresh off the boat, fried jumbo shrimp dinner, cold Yueling & salad. George Carlin is on HBO & its balmy enough to be bare foot & in shorts, w/breeze flowing thru & owls calling.

 

thats so mean.

 

Jealous about the shrimp. The 2002 F150 uses the ~43 degree threshold, for what it's worth--just checked that owner's manual.

It's below freezing here *again* in Michigan, although it hit almost 50 degrees yesterday and I did 20 miles on my bike (bicycle). The "icebergs" on Lake St. Clair, a block and a half away, are smaller than they were last week. I did make the family a pot roast tonight, using a can of Labatts as the liquid. Not as good as mom's, but "comfort food" nonetheless.