>>> A FEW A/C QUESTIONS <<<

[MIDNIGHT RIDER]

My truck, 1985 model, factory A/C.

Located under the hood, right corner, just in front of the fire-wall and behind the blower housing, there is a vacuum actuator that operates a pivoting rod which I assume opens and closes a door.

If the fire-wall was a line running straight through 12-o'clock and 6-o'clock, with the right end being 6- and the left end being 12-, in all positions EXCEPT Max A/C, the operating-arm of this pivot is at about the 1:15 position and the operating plunger of the vacuum gizmo is extended.

Placing the selector in Max A/C causes the plunger to retract into the vacuum gizmo about 1/4-inch and places the arm at about 2-o'clock.

Does this amount of travel seem about right ??

What is the function of this door ??

On the control panel, the top control obviously works a cable that controls a door that opens more or less to adjust between HOT and COLD.


The lower control selects from left to right, in this order, OFF, MAX-A/C, NORM-A/C, VENT, FLOOR, MIX, and DEFROST.

If my understanding is correct, MAX-A/C is re-circulating the inside air through the evaporator, right ??

NORM-A/C is bring outside air across the evaporator and into the cab, right ??

I figure VENT is outside air.

What about FLOOR, MIX, and DEFROST; are they outside or inside air ??

Thanks.

 

[Dave 001]

I figure VENT is outside air.

What about FLOOR, MIX, and DEFROST; are they outside or inside air ??

Thanks.

The only position that draws air from outside is "MAX A/C". I always thought this was STUPID!! During the winter months, what is the point in heating 20deg outside air instead of reheating (recircualting) the cab air?

The "Vent" position is not outside air. It is merely referring to the vents in the dash.

Dave

 

[itsacrazyasian]

The only position that draws air from outside is "MAX A/C". I always thought this was STUPID!! During the winter months, what is the point in heating 20deg outside air instead of reheating (recircualting) the cab air?

The "Vent" position is not outside air. It is merely referring to the vents in the dash.

Dave

Max AC is the only time that door should be closed... Any other time, it'll draw in outside air.

 

[Dave 001]

Max AC is the only time that door should be closed... Any other time, it'll draw in outside air.

DOH!! My brain must have gotten ahead of my typing fingers!! I meant to say "The only position that draws air from inside is "MAX A/C". Sorry 'bout that.

Dave

 

[MIDNIGHT RIDER]

Max AC is the only time that door should be closed... Any other time, it'll draw in outside air.

From my feeble description, does it read like my vacuum gizmo is moving that door the proper amount ??

I seem to remember being able to see this door when I had the blower-motor out, right ??

Thanks.

 

[FORDF250HDXLT]

the blend door should make a very loud and solid "THUMP" sound as it closes when you switch to MAX A/C.
this is the blend door fully closing which recirculates inside air.this is so your re-cooling already cool air,and this is why it freezes your bones and makes you wonder why your doing this to yourself when you just suffered from the winter months not long ago.


"MIX" & "DEFROST" settings will also use the a/c compressor (this is why i unplug it during the cooler months,to help conserve fuel) it's to help aid in quicker clearing of the windshield (not required.non a/c equipped trucks and cars don't suffer any problem,so i opt to conserve instead.) these settings will draw in outside air/the blend door open.

"NORM A/C" setting runs the a/c with outside air/blend door open (probably only partially?) i always switch to this when im froze out and turn the blower motor down.


"FLOOR" & "VENT" calls for no a/c compressor,just outside air/blend door open.

 

[Dave 001]

"MIX" & "DEFROST" settings will also use the a/c compressor (this is why i unplug it during the cooler months,to help conserve fuel) it's to help aid in quicker clearing of the windshield (not required.non a/c equipped trucks and cars don't suffer any problem,so i opt to conserve instead.)

Actually that's not true. My '78 F150 never had A/C & the A/C in my '92 Ranger doesn't work and believe me when the conditions are right (temperature, humidity, rain) the inside of the windshield will sweat to the point that it's running down the glass. And there ain't a dang thing you can do about it. No amount of defroster action with either hot or cold air will dry it out. The air you are blowing across the windshield is already saturated (90%+ humidity) and it ain't gonna dry anything. It's rather dangerous trying to drive when you can't see anything. The A/C in a vehicle (just like the A/C in a house) makes dry air (low humidity). The dry air from the defrosters dries out all this moisture. That's the whole reason the A/C compressor is designed to run anytime air comes out the defroster vents. FORDF250HDXLT, I'm glad you have never been in such a situation but should you find youself having defroster issues, get out and plug your A/C back in. It makes a world of difference. Be safe.

Dave

 

[FORDF250HDXLT]

they're still selling cars and trucks by the millions without a/c (had plenty of them myself lol.) i feel fairly safe unplugging the compressor during the winter,but should the need or desire arise,iv only got to pull over and pop the hood.
kinda makes ya nervous for those without the XLT's hey Dave? kinda like that 4wd to 2wd.once you got to 4wd,you understand how unsafe it was driving a 2wd in the snow lol.

 

[Dave 001]

All I'm saying is it does make a difference and please be safe.

Dave

 

[itsacrazyasian]

they're still selling cars and trucks by the millions without a/c (had plenty of them myself lol.) i feel fairly safe unplugging the compressor during the winter,but should the need or desire arise,iv only got to pull over and pop the hood.
kinda makes ya nervous for those without the XLT's hey Dave? kinda like that 4wd to 2wd.once you got to 4wd,you understand how unsafe it was driving a 2wd in the snow lol.

While there are plenty of vehicles that aren't equipped with a/c. The reason why all cars will default to the defrost position in event of HVAC system failure (so long as the blower still runs). But Dave is correct. the idea of the compressor running in defrost mode is to pull the moisture out of the air, then its reheated through the heater core.

In larger HVAC applications, you have this idea as a TRI-COIL. the idea is to pull as much moisture out of the air as possible, then its reheated for comfort/setpoint

 

[flareside_thun]

Ah, to give a dry heat.....no wonder I've gotta roll down the windows when the heat is running.

 

[MIDNIGHT RIDER]

the blend door should make a very loud and solid "THUMP" sound as it closes when you switch to MAX A/C.

Now we're getting somewhere; I don't hear this "THUMP".

I know the "THUMP" you mean, as I used to hear it years ago.

I am gonna have the wife to listen for it (she can still hear) and if it is not there, then I am gonna investigate farther.


I kinda think that vacuum gizmo is somewhat anemic in it's actions.

 

[RLDSL]

Ironically, the ac compressors coming on with the defrosters and heaters is a fairly recent thing for car manufacturers and comfort/safety was basically the last thing on their mind when it first went into play. WAY back when I was first working in a auto AC specialty shop, no cars had compressors that came on with the heat/ defrosters, and my boss had figured out a long time before that the prime killer of ac compressors was winter, and disuse. As long as we could get folks to fire up the AC compressor at least once a week( wed tell them run it withthe defrost etc, get the picture ), their compressors wouldnt fail, so when they came in to get a failede factory unit replaced ( aalmost always seal failures that lead to worse), they got strict instructions to run that thing once a week, they would last.
Word got around next thing you know a bunch of shops are doing it.... before you know it the new models are coming out from the factory with automatic setups, and the failure rate went WAYYYY down . THe whole dry cabin air bit is really just one of those accidental side effects that they got trying to stave off a warranty repair issue

 

[MIDNIGHT RIDER]

Until reading the responses, I didn't think my compressor engaged for any selection other than MAX-A/C and NORM-A/C.

I am not gonna say it doesn't until I actually check this business out sometime this weekend.

 

[The Warden]

Until reading the responses, I didn't think my compressor engaged for any selection other than MAX-A/C and NORM-A/C.

I am not gonna say it doesn't until I actually check this business out sometime this weekend.

FWIW my truck's an '84 (one year older than yours) and my compressor comes on in "Mix" and "Defrost" as well as the two a/c positions, and according to both the owner's manual and the shop manual, this is how Ford designed it. I don't know when Ford started having the compressor cycle on those two positions, but they had by '84.

Also, I don't know if this will make any sort of difference, but my recirculation door is actually in the "recirculate" position (vacuum applied) with the control lever in two positions: Max-A/C and OFF. I guess Ford decided to have the door in "recirculate" with the system off so that you could have a position where there's no air whatsoever coming through the vents. After looking at both the owner's manual and the shop manual, this was how Ford designed it...