The R-12 to R-134a conversion has been done on my '92 Cadillac Eldorado air conditioner, and a "low A/C refrigerant - service A/C soon" message comes up on the "driver information center".
The air conditioner service people say the refrigerant is full and there are no leaks. How do I correct the computer to recognize the new refrigerant?
Diagnostics on this generation of Caddy have never been fun. Let's assume that the "low refrigerant" message came up immediately after the A/C conversion was completed. This would mean, at a minimum, the R12 refrigerant was evacuated from the system, new pressure fittings were installed, and the system was recharged with the ozone-friendly R134a. The correct type and amount of refrigerant oil needed for the conversion was included in the mix.
Two items to keep in mind: one, be sure the R12 was completely removed from the system (can't mix the two), and two, the system should be charged with about 10% less R134a than the recommended capacity for R12.
R134a operates at higher pressures so we don't need quite as much. The warning message tells me that trouble code AO46 was stored in the air conditioning programmer memory. That may be Arabic to you. But translated, the system believes you are low on refrigerant because it sees an abnormal temperature reading from a temperature sensor on the low-pressure side of the A/C system.
Get it to a Cadillac service department. This system can be tricky and nobody knows it better. They'll check for codes, scan for relevant data, and possibly just clear the trouble code to see if it comes back.
I would check, and double-check, that the system is fully charged. Technicians can inaccurately determine a system to be full by observing pressures, as opposed to measuring the exact amount of refrigerant going in.
After that's all said and done, the top possible causes to the warning light would be a bad low-side temperature sensor, a restriction in the A/C system which is affecting refrigerant pressure (obstructed orifice tube is common), or one of several other temperature sensors being out of whack, confusing the first one.