92 Cadillac Deville

F48 is low(or very low) refrigerant. First is to verify that the system is indeed low, and search for the source of the leak. Some common places are the compressor, and the evaporator core. If it is not too low, and the code will not clear, then you would need to be versed in the onboard diagnostics, to navigate your way to sensor values and see if one is reading faulty and causing a false low reading.

Low refirigerant may not have a direct relation to heating concerns, and it is not a dual zone system. Perhaps something to look at, would be the operating temperature of the vehicle is low enough the heat is noticed on the passenger side since it is closest to the heater core. The temperature of the coolant may be insufficient to provide adequate heat through the entire system. Check that the engine is heating fully, you should not be able to keep a hand on the upper radiator hose for more than a few seconds if it is heating fully. If you can keep contact as long as you want, the thermostat may be stuck open, or improperly regulating the temperature. Usually when an F47/F48 code sets, the compressor is disabled as a default to protect the compressor, as refrigerant oil is carried in the refrigerant.