Here's what's involved in a proper conversion:
1. System Inspection and Leak Check:
* Thorough inspection: Before doing anything, you need a complete visual inspection of the entire AC system for leaks, corrosion, and damage. Look closely at all lines, hoses, the compressor, condenser, evaporator, and drier. Any significant damage needs repair or replacement before proceeding.
* Leak Test: A professional-grade leak detection should be performed. This is crucial to identify even small leaks which would be exacerbated by the new refrigerant. Using a dye and UV light is common.
2. Component Compatibility and Replacement:
* Oil Change: R12 and R134a use different oils. The R12 oil is incompatible with R134a and needs to be completely flushed out and replaced with PAG oil compatible with R134a. This often requires complete system disassembly.
* O-rings and Seals: The system's seals and O-rings may not be compatible with R134a. These should be replaced with R134a-compatible parts. Some seals may swell or leak with the new refrigerant.
* Expansion Valve/Orifice Tube: These components may also need replacing; they're designed for specific pressures. A conversion kit will often include this part.
* Compressor: Depending on the condition and type, the compressor might be able to handle R134a with a proper oil change. However, it's recommended to check for compatibility with a reliable mechanic.
3. Conversion Kit:
* Purchase a conversion kit: These kits typically include the necessary PAG oil, R134a-compatible O-rings and seals, and sometimes an expansion valve/orifice tube. Make sure it's specifically designed for R12 to R134a conversion.
4. Evacuation and Charging:
* Vacuum: The system needs to be thoroughly evacuated to remove all the remaining R12 and moisture. This requires a vacuum pump capable of achieving a deep vacuum. This step is absolutely critical to prevent damage.
* Charging: Once the system is properly evacuated and the new components are installed, the system can be charged with R134a refrigerant using a set of gauges. The amount of refrigerant needed will depend on the system's specifications. You'll likely need a manifold gauge set to properly charge the system.
5. Professional Help:
* Strongly recommended: Unless you have significant experience with automotive air conditioning systems, do not attempt this yourself. Improper conversion can damage the entire system, requiring costly repairs or replacement. The cost of doing this yourself improperly could easily exceed the cost of having a professional do the job.
In summary: Retrofitting R134a into your 1991 Mercury Capri's AC system is a complex process requiring specialized tools, knowledge, and parts. The safest and most reliable approach is to have a qualified automotive air conditioning technician perform the conversion. Attempting a DIY conversion risks significant damage and expense.
