Automotive Air Conditioning Information Forum

I am trying to follow the factory procedure for converting my 91 Porsche from R12 to R134a. I have removed the compressor and drained all the oil I can from the ports (there is no drain plug). I have a home vacuum pump and manifold set from harbor freight. They both work well but do not separate refridgerant from oil and I have no idea if oil is actually being pulled. Any assistance appreciated.

Factory Procedure:

Procedures

Retrofitting of air conditioning systems to refrigerant R134a:

Important :When working on air conditioning systems, observe safety precautions for operations on the air conditioning system and for handling the refrigerant (also refer to Repair Manual, Group 87).

1. Before starting retrofitting, check operation of air conditioning to see if additional repair operations are required on the air conditioning system (e.g. faulty piping, inoperative compressor and/or system leaks).

2. Connect recycling service equipment for refrigerant R12. Extract and dispose of refrigerant and refrigerant oil properly in accordance with instructions. Measure and make note of the refrigerant oil volume that has been drawn off.

3. Refill the system with the entire R12 refrigerant volume drawn off without the refrigerant oil.

4. Start engine. Switch on A/C system and run engine at approximately 2,000 rpm for approximately 10 minutes. Operate the A/C system to mix any remaining refrigerant oil with the refrigerant so that it can be drawn off.

5. Draw off refrigerant and refrigerant oil. Measure refrigerant oil volume and add to volume determined under item 2. At least 50% of the specified refrigerant oil quantity (see system specifications in brackets) should be removed from the system.

If insufficient refrigerant oil was drawn off or drained, proceed as follows according to the compressor type:

a) Compressor with drain plug:
Remove drain plug to drain refrigerant oil.

b) Compressor without drain plug:
Remove compressor and drain refrigerant oil at port connections.

c) Refit compressor.


6. Carry out any repairs that might be required on the air conditioning system (see item 1). Replace the receiver dryer (see chart) and install without any delay after removing the plugs. Replace O-rings and coat them with fresh ND-Oil 8 refrigerant oil.

7. To allow the R134a service equipment to be connected, fit the required adapters (angle valves or straight adapters, depending on space constraints) to the previously used connections.


New charge:

8. Evacuate system with A/C in maximum position. If system evacuation is successful, proceed with item 9. If not o.k, proceed with troubleshooting (leak) and repair.

9. Fill in fresh ND-Oil 8 refrigerant oil (for volume see charts) using service unit or external filling unit.

Note nly use new oil, used refrigerant oil extracted from an A/C unit must not be re-used.

10. Evacuate system again for approximately 1 hour. Run leak test in vacuum section (the vacuum generated must be maintained for approximately 2 minutes).

11. Fill with specified quantity of refrigerant R134a.

12. Run engine. Check for output and leaks at an increased high pressure of approximately 18 bar. To reach this high pressure, switch off the fans briefly by disconnecting the wiring plug.

Converting a 1991 Porsche to 134a is like shooting yourself in both feet with a 12 gauge shotgun.

Just keep it R12.

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No, oil is not pulled out with the vacuum.

However, you also said "along with refrigerant" - to be clear, you do not "extract" refrigerant with a vacuum pump.

That factory write up is fairly convoluted and worded odd.

Empty the system, add your correct oil type (usually ester oil for conversions) and amount, close up the system, vacuum (at least one hour), let it sit for a while to make sure it's holding vacuum, then charge with refrigerant.

r-mm - if you're in USA, it's still legal to use R-12 in an AC system designed for it. And legal to buy R-12, just need to get the 609 certificate. And in Phoenix there are still shops who repair R-12 systems, because there is still a classic vehicle clientele.

Myself, just about 4 days ago I evacuated and filled my 1988 Mazda truck with R-12 that I'd purchased decades ago at about $2 a can. R-12 can be a little pricy, a little strange because there's a big supply hoarded and little demand, as so many since 1994 have done or tried conversions, or pre-1994 vehicles are simply off the roads now. I had a leaky service valve cap.

Thank you all for the responses. I looked online but can not tell what a 609 Certificate is or where I should be shopping for R12? I do not have an a priori need to convert to R134a, I just do not want to be hard pressed to find R12 and in my experience working on old cars, fixing the AC can involve removing / recharging the system many times while leaks are found and components are replaced.

Where does a home hobbyist purchase R12 and what is a reasonable price?

Look for R12 on Craigslist or Offer Up or eBay. I have always found them to be more than plentiful on all those platforms, even to this day.

Expect to pay about $25-35 per 12-14 oz can on Craigslist or Offer Up, and probably $45-50 per can on eBay on average. There's a whole case of DuPont 12 oz cans on eBay right now for $380 shipped, which works out to a tad over $30 a can. That might be a good pickup if you're looking to keep an old R12 car long term. There's quite a bit on eBay right now and frankly most sellers don't require the license, and instead just state in the ad that it must only be used by qualified technicians etc.

Personally, I bought a 50 lb jug of R12 on Craigslist a few years back for I think $500 that I've been using on my old cars.