RLXXI

They are exactly the same, here's a snip from the shop manual.


When MAX A/C is selected:

• the air inlet door closes, preventing outside air and allows only recirculated air.
• the RECIRC button is disabled and the indicator is illuminated (RECIRC forced on).
• the mode doors direct airflow to the instrument panel A/C registers.
• blended air temperature is available.
• the A/C request button is illuminated and is disabled.
• the A/C compressor operates if the outside temperature is above approximately 0°C (32°F).
• the blower motor is on.

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When PANEL is selected:

• the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
• the mode doors direct airflow to the instrument panel A/C registers.
• blended air temperature is available. Only when A/C compressor operation has been selected by pressing the A/C request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
• the A/C request button is enabled. The A/C compressor operates and the indicator illuminates if the A/C request button is selected and the outside temperature is above approximately 0°C (32°F).
• the blower motor is on.

RLXXI

Ok interesting result with evap temp with my command of the clutch, the vent temp again at 20*F. I had to switch from PCM to HVAC module to get the evap temp probe reading and as a result of the time lapsed between module connection from one to the other I was able to view in IDS evap temp @ 3.6*F and climbing.





Colder than a meat locker.


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Engineer Guy

I dialed down my A/C Potentiometer to ~300k Ohms. Just because I could. Vent Temps on 'Recirc' with Fan on '4' hit ~35 F. My Heat Soaked Cab dropped from ~110 F to ~74 F after 10 minutes driving. Man, I'm now driving about anywhere I can on any excuse; even in the 97 F Temps of yesterday. I did get a lil whiff of some smell at this low Vent Temp [not a bad smell], and it promptly disappeared. This, at ~18% Cab Humidity. Unlike the other day, no Frost production was evident.

I repeatedly see 'MAX A/C' Mode drop Vent Temp about 1 additional Degree over 'Recirc'. In separate News, the Compressor Cycling really tightens up at low Temps. 'Off' at ~35.8 F. 'On' at ~39.5 F. A couple of Degrees higher Vent Temps on 'Recirc'. A couple of Degrees higher still with Outside Air. In that Mode, it was ~44 F to cycle 'On'. ~41.3 F 'Off'.

When Heat Soaked to >110 F, my passive Vent Temp always read >20 F Degrees higher than the Floor Temp at the Cup Holder. So, I had no problem believing that Vent Temp with A/C running would be 'much' higher than Evap Temp. Physics 101. The Vents run under a black Dash, and just behind the hot Firewall. Vent Air heats up some as it travels along in that un-insulated environment.

I'm heading out tomorrow to Fish while towing our new RV Trailer. 5,205 Lbs from the Factory. 7k Lbs. max when loaded up [Trailer Spec, and high side guesstimate]. Likely less while I'm Flying Solo tomorrow. I'll see if Cabin Temps creep up on this long drive. I'll power cycle 'A/C' Mode if it does and - in separate Tests - dial down my A/C Pot to see if that adjustment lowers/resets 'creeped-up' Cabin Temps over time.

Thanks for the great Data Rnlcomp! In all your Posts...
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digitaltrucker

Yep the closer cycle point removes that uncomfortable feeling that you feel at 42 46.

Good luck!

RLXXI

Hey just trying to help the cause, cause Ford dropped the ball. Kudo's to all that contributed, collaboration works! Have fun on your trip.
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jlinville

I get the smell right around 40*. It is brief, but will come back occasionally IF it gets down to 40 again. As hot as it's been outside, I normally see around 42*.

This sounds like a great idea!!!

I've got my potentiometer set at 325K also. I'm thinking about dropping it down to 320K and see if I get a few degrees cooler.

When I turn on Max, it gets colder initially, but then starts to get several (5-10*) degrees warmer. I turn it off and just click on recirc and it starts to cool down again.

digitaltrucker

Finding on the donor truck that auto or normal have been very capable at about 325. But the wife still laughs!

Old Smoky

A/C is working great on Max Air Recirc, Normal A/C is back to old ways I think;

Engineer Guy

As suggested above, I noted some informal results while Towing just shy of 7,000 lbs [guesstimate].

A/C Vent Temps and Cabin Comfort were unchanged, insofar as the A/C keeping up. At 90 F Degrees ambient on a steep ~4 Mile climb, the Compressor did cut out when Radiator Temp rose off the usual 1/2 way mark to the 3/4 mark. This was while winding out in 2nd Gear in 'Tow Haul' Mode at ~60 MPH. I then crested the Hill Summit.

What I'm seeing in dry Colorado is that Humidity is the biggest Variable. At ~20% Humidity, Vent Temps from 37 F to 41 F are just fine, and reproducible. After a Rain Storm and ~35% Humidity, the A/C froze up twice on different days in 'Recirc' Mode. But, not since. When apparently frozen, Cabin Temp climbed to 50 F or so. I turned off A/C immediately. Frost 'chunks' about the size of Air Rifle BBs then blew out the Vents momentarily [just once], and the System resumed prior low Temp operation when A/C was turned back on with 'Recirc' on.

Once, Cabin Temp rose to ~50 F w/o visible Frost when Vent Temp was around 37 F. I'm wondering if such freezing is the cause of this 'sudden' Temp excursion that others have noted? Especially when turning A/C off - then on - resumes low Vent Temp A/C performance.

When this happens, I can hear Fan noise change [lessen], warning of this blockage. Or, so I perceive...

I'm also seeing Vent Temp climb in what appears to be a controlled manner right when the Cabin Temp hits 65 F [18 C]. Comfort is maintained, however. I'm suspecting the Cabin Temp Thermistor is preventing Cabin Temp drop below this point while in 'Recirc' Mode. This behavior has happened repeatedly. Fine by me. I'm comfy to cold by then.

Other than these Humidity-based Freeze-ups, I'm happily cruising along in my Meat Locker Temp Cabin. Vent Temps yesterday were 37 F in 90 F ambient Heat and >20% Humidity during a long drive. I'm fiddling with Pot Values - and establishing A/C System trends - from ~450 kOhms down to ~250 kOhms. I'm sticking with higher Pot Resistance values to avoid damage.

Lovin' Life!
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digitaltrucker

Thanks!

Weather in Houston has cooled somewhat, so it may be time to return the system to normal in the donor truck.