Something is wrong with the Lexus. The computer should not allow the evaporator to get below the 32 degrees to prevent freezing. Your truck is going as low as it possibly can and is working perfectly.

 

The Lexus A/C system is *not* getting down to 13° or 6°F. Period. As mentioned above, an IR thermometer will be (and is proving to be) wildly inaccurate for this type of measurement. A mercury thermometer or probe-style electronic one is needed here.

 

The new refrigerant must not be as good. My Mustang seems to get colder, and get cold faster than my truck, and it's 13 years old.

 

A properly-engineered A/C system can achieve the same cooling performance regardless of refrigerant being R-12 or R-134a. Now, convert an R-12 system to 134a, and yes, you will dee diminished performance.

..

 

Your Mustang and F-150 use the same refrigerant. Ford didn't switch to R-1234YF until the 2017 model year even though it was supposed to use it in 2015 but the Honeywell couldn't produce enough for F series production. As a matter of fact if you look at some of the A/C hoses in your truck they will have "R-134A/R-1234YF" markings indicating they are suitable for both refrigerants.

As technology gets better A/C systems get more efficient. They can cool as well with less refrigerant. R-1234YF is very similar to R-134A which was done on purpose to reduce the cost of changing components for manufacturers. The biggest difference is the requirement for a internal heat exchanger to improve efficiency. The downside is that R-1234YF is waayyy more expensive than R-134A.

 

A/C performance is fully dependent on ambient temperature and humidity (a 25ºF delta is considered good performance). You'd have to measure 2 cars at exactly the same time to be comparable, and also turn the compressors on at the same time, on lowest temperature, and both in either fresh or recirculation. In other words, exactly the same conditions. My beef is with the electronic systems. My truck cools very well, but just noticed on this last trip, as it gets hotter outside (near 100), air gets warmer all of a sudden, which makes no sense, since temp inside should be kept the same (i typically have it at 72). When I lower the temp to 70, air gets colder right away, but it's too cold when it gets to about 95. So yet another car with an idiosyncratic HVAC. Ha ha. But I'm used to it by now. Not a big deal. At least it cools well enough even in 100F+ heat, so no complaints from me.

 

Would you happen to have Auto/dual heat/air where you can set your temperature and the truck would keep it there. I had played around with it in my XL even though I don't have the dual heat, but when I would use the auto air, 72-73 seemed to be a bad spot, it was like the air would stop and I would get slightly warm air, if I turned it down to 71, the air would come right back on. I just gave up on the fancy system and went back to my original system.

 

Poor programming can make an auto system suck. My aunt has a GMC Acadia with an auto system and that thing will blow on max fan until it gets to the set temperature. It doesn't slow down as it approaches set temp instead it blows on max speed until it reaches set temp. My Acura on the other hand works well on auto. In the daytime I usually set it to 68 and at night or cloudy days 70 or 72, to me 72 during the day is kind of hot. It cools quickly and quietly and is accurate. The cool thing is that it's linked to the GPS system to compensate for the sun's position. Using GPS, time and the solar sensor it knows where the sun is relative to the car's position and how intense it's shining. If the sun is on one particular side it will automatically use the dual zone system to compensate by blowing colder air out the side where the sun is, especially the driver's side. Usually you can't tell it's working but during drastic changes in direction like a interstate cloverleaf or steep curves you can hear the fan ramping up as the sun moves around the car.

 

Where did you get it ? What does it cost ? How many bottles for the system ?