BosAg

Yes. I've had the long trip failure and yes my suction line is wrapped also...

cwdaniel

Got my OEM connectors this week so I figured I'd document my install. So far so good, no more worries on possible erratic problems from jiggling connections. The OEM stuff came with some quality butt connectors and heat shrink with sealer. Nice!



OEM connector set




Resistor connector




Splice with added wire for resistor. Crimped and soldered




With resistor connector installed




200k and 300k resistor married. Ohms out to 490k




Resistor connector pins Crimped and soldered




Resistors and connector installed covered with heat shrink.




Finished and able to swap in resistor or a pot if need be.

jlinville

Mine is wrappped!

digitaltrucker

Ok we need an unwrapped test.

Jwgmn

Mine is unwrapped. I have factory plug ends with 1meg potentiometer. What do you need?

JJM

Mine is unwrapped. I have the warming after a while on the road. Experienced it wrapped and unwrapped.

digitaltrucker

Just wanted to see if it being not wrapped, would prevent the freezing.

JJM

I don't experience freezing. At least, not that I can tell.

Feathermerchant

We just drove from DFW to ABQ and had no warmup. Every time I checked I saw about 42=44 degF. We used recirc almost all the way. We stayed very comfortable. I had to close a vent. It was 88 deg up to 94 then we hit some rain and it dropped to 73. At 70 deg we turned the A/C off but that was within 40 mi or so of our destination. Maybe the truck never got cool enough inside.
I am using the 1MΩ resistor.

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

Elevation - 6,150' - ~18% less Air Density than @ Sea Level.

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.
.