OK, as regular visitors to the forum already know, I recently converted the A/C system on my DeLorean to run on R-152a (aka Ultra-Duster/Dust-Off/etc) as opposed to the stock/OEM R-12 (which now requires an EPA certification in order to purchase lawfully).
The problem that necessitates having to perform such a conversion is two fold: 1) a relatively small/minor leak in your system has caused enough of the stock/OEM R-12 to leak out of the system that such has rendered the system either ineffective or completely un-useable in its present condition; and 2) a desire to avoid obtaining the requisite EPA certification and pay the often times comparatively high prices associated in securing replacement R-12 refrigerant for your system.
Of course, there could be other reasons that rendered the A/C on your particular car from functioning, but the scope of this tutorial will focus solely on the refrigerant conversion of an otherwise functional system.
The first course of action in such a conversion should be to familiarize yourself with the basic layout and functioning of the components involved in the A/C system, a standard General Motors / Harrison Radiator fixed orifice design, with six primary components - the compressor, the condenser, the orifice tube, the evaporator, the accumulator (aka drier), and the low pressure switch.
The locations of these components are as follows:
Compressor: engine bay mounted via brackets off the driver's side valve cover
Condenser: behind the front clip/fascia and in front of the engine cooling system's radiator
Orifice Tube: in the feed line between the condenser and the evaporator where the line turns into a metal pipe and passes thru the fiberglass tub / bulkhead
Evaporator: within the cabin of the car inside the climate control / ventilation box on the passenger side end of the box
Accumulator: mounted to an exterior fiberglass tub wall in the front passenger side wheel well
Low Pressure Switch: mounted to the accumulator
Essentially, the compressor takes gaseous refrigerant and compresses it into a liquid and sends the pressurized and heated liquid refrigerant to the condenser, which cools the liquid refrigerant via the passage/draw of forced ambient air over the condenser (either via virtue of the car's motion or the activation of the car's electric cooling fans).
From the condenser, the liquid refrigerant travels to and encounters the restriction of the orifice tube (which acts as a barrier between the high pressure side of the system and low pressure side of the system), which focuses/concentrates the liquid refrigerant into a small narrow outflow passage, essentially atomizing it (kind of like a fuel injector), which has the effect of rapidly expanding the liquid refrigerant passing through it and lowering the pressure / temperatures of said liquid refrigerant to the point that it changes state as it heads to the evaporator.
It's in the evaporator that the pressure / temperature of the liquid refrigerant falls so low that it reverts back into a gaseous state, the effect of which causes an additional lowering of the temperature of the now gaseous refrigerant. As the cold low pressure gaseous refrigerant travels through the evaporator, outside ambient or cabin air is drawn across/through the evaporator by the HVAC blower motor (fan), which is cooled/chilled by the coldness of the gaseous refrigerant filled evaporator, and is then pushed by the blower motor (fan) through the ducting system, out the vents, and into the cabin of your car.
From the evaporator, the now gaseous refrigerant heads to the accumulator, where it is filtered and dried of any moisture that may have infiltrated the system (or been present in less than pure refrigerant products) and mixes with miscible lubrication oil that has accumulated there by virtue of system operation. Attached to the accumulator is the low pressure switch, which monitors the pressure of the gaseous refrigerant passing through the accumulator, and controls the activation/cycling of the compressor based on such pressures at the range in which it has been adjusted/calibrated to work within.
The gaseous refrigerant (low pressure/low temperature) then travels back to the compressor, where it's compressed back into liquid form and the cycle begins all over again.
You can follow the process/cycle from start to finish on the image below:
Here's a visual representation of the functioning of a similar style system (expansion valve), albeit the function and location of the accumulator in such systems is different:
Now that you have a basic understanding of the system components, their operation/function, and their locations on the car, we're ready to dive into doing our conversion with the required (and optional) parts list!