Want Really Cold AC/92 Brougham Limo

Been working on optimizing the AC on this 1992 Brougham Limo
(6 door) before the Florida summer gets here. It does cool "OK"-maybe 55 F at the front vents.

Anyone know where I can get a Evaporative Inlet Temp Sensor for the 5.7 Brougham? The system will have to be evacuated and opened to replace it so would like to have it on hand whenever I need to do that again.

The total amount of refrigerant for a stock Brougham is 3.3lbs R-12. How much more (ballpark) should be required since there is an added rear evap unit and additional small condenser? I guessed at 1lbs.

The new R-4 compressor I installed, which is for both the front and rear AC units, is cycling on and off too frequently after operating for 2-3 minutes. It cycles on for 5 seconds and then off for 8 seconds repeatedly. The ECC is showing the evap inlet temp going below O C and that is when the clutch deenergizes like it is suppose to do. Don't have an IR thermometer so haven't been able to verify that this temp sensor is calibrated correctly and would like to replace it eventually.

This sensor is peculiar to the 5.7 liter. The 5.0's have what they call a Thermostatic Cycling Switch-which the manual says does the same thing. They deenergize the clutch if evap temp (refrigerant temp) is less than 0 celcius.

Initially thought I might not have an adequate charge but the ECC shows that the Low Pressure Switch is not not deenergizing the clutch. Gauge pressures showed Low 30 psi, High of 170psi two days ago at an ambient temp of 70 F when I charged the system. I had the water hose spraying the condenser while charging. Today at 83 F the gauges showed 50 and 280-no water hose. So I think I have an adequate charge and the The evap inlet line and the accumulator/drier are both cold but not frosting, which from my reading indicates an adequate charge of R-134.

This car is pretty much stock so original condenser (non-parallel). The add on condenser has an electric fan which isn't working but will tomorrow after fixing wiring problem.

This what have done so far:
-Front AC unit have put a new AC Delco R4 compressor/ Evaporator/Expansion Tube/ Accumulator Drier/New O-rings where ever system opened.
-Rear AC replaced the expansion valve and liquid refrigerant solenoid valve.

According to the sticker it was switched to R134 in 2001.

Any suggestions on getting more cooling out of this unit?
 
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