Originally Posted by Engineer Guy

Thanks to the fabulous Info on this Thread, I finally got around to my own quick & dirty Mod using a 500k Pot w/integral On/Off Switch from Radio Shack.

In the Engineering Trades, my Testing today was intentionally confined to 'Proof Of Principle': 1. Does the Pot I chose work? 2. Does it work on my Year/Model of Truck? 3. Did I achieve what we used to call 'The Desired End Results'? I.e., a much lower and wider range of Temps out my A/C Vents?

Mission Accomplished!

Because I could not make reliable temporary connections at the Connector leading to the embedded Thermistor, I used my old Troubleshooting trick of shoving 2 Push Pins through the Wires. I ran thin Wire ~3' out to the Pot. I don't have time for a Spreadsheet, so here's my Test Results.

2014 STX SCab 4x4 - 5.0 Liter - Manual Single Zone A/C - No Sunlight Sensor by Windshield - Factory R-134a Charge - not Gauge verified. Uncalibrated Radio Shack Indoor/Outdoor Thermometer. Thermometer Outside Temp Sensor stuck in Vent immediately to Driver's Right. Temp readings below were logged after ~5 minute Test intervals.

Outside Temp in Cloudy Weather - 81 F Degrees

Cabin Humidity - 22 %

Cabin Temp - 84 F

Vent Temp Setpoints - Stock - 44.3 F 'Low' - 47.4 F 'High' during Compressor cycling.

'MAX A/C' setting w/Recirc used at all times in stationary Truck. Loud Aux Radiator Fan on ~70% of the time. Again, this Test was restricted to only Pot-related effects; not a full range of findings. Like, what is the outcome of a long drive, or what is the outcome in 105 F Degree Weather? In my experience, it is critical to reduce the number of Variables during Test in order to reach reproducible conclusions.

~450k Ohms Pot setting didn't have 'much' effect. Perhaps an A/C Vent Temp of a degree or two less; relative to the Stock Setpoints above.

~250k Ohms Pot setting - 39.4 F 'Low' - 41.7 F 'High' Compressor Cycling

~125k Ohms Pot setting - 34.3 F 'Low' - 36.9 F 'High' Compressor Cycling

Testing was then terminated to avoid potential freezing. Given the low Humidity, there was no liquid pooling under Truck when I moved it. My Cellphone and Voltmeter were actually cold to the touch when I moved them after ~1 hour of Testing. As we established in College, what a difference a little Pot can make!-)

A ~$3.50 Pot from Radio Shack, and the amazing wisdom in this Thread, led to a drop of exactly 10 F Degrees in Truck Vent Temp output! I will not keep Vent Temps that low. However, it's nice to know what's possible; and it verifies the lower 'end point' possible with this Mod. Also, note that Compressor On/Off Temp spread was reduced. I also really liked the 'new' alternative of directing A/C Air Flow to both my Feet and my Torso. This was not possible prior because Vent Temps were too high to cool both Cabin regions to comfortable levels.

The pending, final Install will use a Ford Harness to attach this Pot to. I will wire through the integral Pot On/Off Switch to remove this parallel Resistance from the Thermistor Circuit seasonally. I will use an old Guitar Amplifier Volume **** mounted discretely to provide a relative adjustment reference. I chose the 2 Pot Tabs whereby clockwise rotation - higher Resistance - results in relatively higher Cabin temp/Compressor Cycling Temp Setpoints.

I like the relative quiet of Outside A/C vs. Recirc, or Max Air. Air. Drawing in Outside Air using 'Regular' A/C Mode led to higher Vent Temps during Test of about 3 F Degrees while stationary. I will use 'Max A/C' Mode initially to cool a Heat-soaked Cabin, or in high outside temps.

As one can see in the excellent Calculations and Info nicely provided up-Thread, the Thermistor takes very low current. This is why the Wires to it are so small. No need to worry about Wire length/size to an outboard Pot, or to use any Heat Sinking. FYI, Thermistors are commonly used in House HVAC Thermostats, for example.

I've insulated my A/C 'Cold' line; as documented in my Write-Up here elsewhere. I also plan to retrofit ~R-7 'Astrofoil' - a.k.a. 'Reflectix' - behind my SCAB Rear Seat, and in the Doors, as I upgrade my OEM A/V System.

Thanks - and thanks again - to all the tenacious Contributors here. I had my first Ham Radio Station at age 12, and built large P.A. Systems after College. Spent most of my Career in precision Measurement Instrumentation, and Electronics. The range of generous Info in this Thread really floated my proverbial Boat!

We're away soon in our new RV Trailer in early Retirement. I'll report in with any long Trip A/C perturbations, or pertinent findings. I'm guessing that clicking off the Pot - then clicking it back on - will cause the A/C Temps to drop again; removing the vexing long Trip problem where this Pot solution works so well initially, then sometimes doesn't. As with most Electronic/Control Systems, resetting or rebooting often corrects abnormal System behaviors.
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Originally Posted by TheSlimOne

I am running a 470k ohm resistor, here in DFW its been about 100-106. The A/C is doing SO much better. It runs about 42 or so out the vents. I used to have to keep it at full blast non stop to feel like it was doing much. Now after a couple of minutes I can turn it down a bit. Why the hell does ford think that this is ok. JUST NUTS!

I may drop the resistor down a bit. I dunno. I am pretty happy with the way it operates so far.

Originally Posted by Engineer Guy

From LOCO LAPTOP...

'It's even colder when its cool outside.'

The lil Radio Shack Indoor/Outdoor Thermometer w/Humidity Sensor I'm hauling around in a Cup Holder just off the Floor has become the most important Gauge I'm referencing, vs. a new DVM. Job #1 is determine the Vent Temp -> Cabin Temp when comfortable. Job #2 is to correlate Pot [or Resistor] Ohmage to makes that comfort happen.

I've managed to make a lil Ice in my A/C when Vent Temp hit ~38.5 F. It blew out of a Vent, like flicking the top of a Snowcone. When I immediately shut off A/C, and kept the Fan on, I could hear 'something' drop within the System [Frost]. Cabin Humidity lept up to ~58% from ~24% as this Frost melted. Things returned to normal in a few minutes. No harm/no foul. The second time I made a lil Ice/Frost, the Cabin Temp climbed quickly; suggesting that insulating Frost was impeding 'Cold' exchange. Vent Temps were cycling from 38.5 F -> 40.4 F when this suddenly happened. It appears to take 'some' time... I suspect that the tipping point of Frost creation is due to Cabin Temp steadily dropping while on 'Recirc'.

So, if Resistor Value 'x' is netting Temps in the low 40s, I'd suggest that's perhaps as low as you want to go. Nothing succeeds like success. I'm gonna test on into the Fall, since Colder In -> Colder Out. Meanwhile, when Cabin Temps hits the mid-60s [amazing!], the System does a great job of increasing Vent Temp 'some' to maintain this. I assume this is the Thermistor/Circuitry to the Dash right side of the Steering Wheel doing it's job.

While Idling in 90 F Degrees with the Vent Temp around 40 F, I suddenly couldn't get the Vent Temp below 50 F to save me. 'High' Radiator Fan setting never kicked on. I first thought I'd lost a connection in my Homeboy Wiring setup. Nope. Nor was the System creating Frost. Only driving away made my System drop back to the high 30s - low 40s. This was all on 'Recirc' with Fan on '4'. Not much 'MAX A/C' anymore. No need, EXCEPT for the first few minutes IF the Cabin's Heat Soaked. Like, the ~110 F Cabin Temp I hopped into yesterday. MAX A/C drops Vent Temps another degree or so. This makes freezing more likely. No Kids/No Wife driving my Truck to damage things, so I'm gonna tweak away on Pot settings throughout the ~400k Ohms range.

Reducing Fan Speed changes Air Flow, and thus 'Cold' being conducted away. I'm still playing with that factor while watching Vent Temps.

The 500k Ohms Radio Shack Pot I'm dinkin' with has lil index 'clicks'. So, my Sweet Spot Temp setting is 2 or 3 'clicks' CCW back from the 500k Ohms at full CW. This is in my 2014 SCab with Factory [minimal] Window Tint. I eventually want to seasonally set my System via Pot indexing 'clicks' vs. carrying a Temp Gauge forever.

Originally Posted by digitaltrucker

OK I am going to throw this out to everyone now. Have you noticed since your coil is cooler now, the "dirty sock smell"?

Originally Posted by MDBoostWorks

That would be from more condensation in your evaporator box, when you park the truck any condensation that doesn't drain out will form some mildew and cause the funky smell. Probably really strong when you first start the truck and turn the air on then diminishes right?

Originally Posted by digitaltrucker

Actually, no. We can be driving along in the donor truck and one of the wives will say: Theres that smell coming from the AC!

So no not on start up at all, but that is the norm.