I prowled the you tube tonight to find layman’s talk. The chart people will drive you bonkers but the charts have their place, mostly hidden away someplace! (-:)

Now on with the rule of thumb in action!

He uses 20 degrees as his constant but it can be as high as 30 degrees under idea conditions in most cases.
This gets proved later.
https://m.youtube.com/watch?v=15ZrpM41enE

Now you will hear 30 degrees mentioned as rule of thumb on and older 10 seer A/C before 2010. Phased out R-22.

Here:
https://m.youtube.com/watch?v=c3IieMtRMUQ


Now with a different refrigerant R-410 along with the quickly mentioned larger condenser, now for me, the game is on with big units he mentions. You need equipment to be tough 24 hours a day!
It also shows a thermal expansion valve for the metering device to more effectively flood the evaporator. Again a sensor is needed.

The rule of thumb number changes to 25 degrees change in temperatures Thumbs come in different sizes but the whole theory is the same thing!
On a car, with the radiator next to the condenser, it’s tricky to get true temperatures, so, this wiggles my thumbs!
Just look for change down the condenser.
Do you have a digital thermometer with dual leads or infrared thermometer?

Here:
https://m.youtube.com/watch?v=JkaG_F-9hD8


Note the tremendous difference in working pressures that he talks about with the R-22 replacement R-410. It must move more BTU’s per pound or its sent around more times at those pressures. Like R-134a is different too!
In my book this means more work has to be done but he says it’s a SEER of 13. This is supposed to be better. ?????

Nowadays it’s higher up than this but the power to the compressors motor and speed is controlled more tightly, electronically, to the “sensed” heat load!
The coils of units are limited to space, as I mentioned before and the TXV.
Not a fix orifice as it’s just not a dynamically cheap way to go anymore. The deal is on the electric power modulation.

SEER 13 is a more costly unit to purchase up front and payback time, well, if you truly get into the nuts and bolts, it is longer!
Today’s refrigerators are being sold as to only last Ten years? Say what?
Consumers must be aware of this, in a throw away world!

Notice the amount of space drawn above the two different coils, showing the states of change and the magic happens on either side of the cycle.
That space or balance is crucial to the design of the orifice in our cars.
The variable and the fixed orifice need to be nailed into those zones of the enthalpy charts for each refrigerant. This is where I stress the importance of watching evaporator icing

The Rules of Thumbs for superheat are protection (mentioned as insurance) to keep the hammers away from your compressor.

You said the other one just stopped and that got you into doing the repair.
I’m even more curious to what you are going to find out about the car system.

Phil