R-12 to R-134 conversion

[Matt B]

Sorry, I have to dig this out once more as I'm close to my plenum pull and will do the r134 conversion then.

Question is about oil and I still haven't (but might have overlooked) found a sufficient answer. How and to which extent (!) the old mineral oil has to be removed? It can't be simply flushed with r134...

I'm asking because particularly the above mentioned PAG oil is to my knowledge not compatible with older mineral oils. The alternative would be PAO 68 which can be mixed with minerals, but it's PAG that is explicitly mentioned.

So are there any efforts recommended by the bulletin to remove the old oil other than draining what's in the compressor and replacing the dryer?

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[Thomas ZR-1]

I refill the R12 systems with the regular R134a for about 10 years now via R12 to R134a adapters and replacing the following: filter dryer and ALL pipe o-rings.

Glaub mir Matthias, funktioniert problemlos...und: anstatt 960 Gramm nur 840 Gramm K?ltemittel einf?llen wegen der anderen K?ltemittel-Dichte, sonst tut sich der Kompressor schwer.

[Matt B]

I did the conversion today. Following most suggestions I used PAO oil (which nicely blends with R12 mineral oil) following the shop manual guides.
I replaced the dryer by an AC Delco genuine part and added 105ml of oil into the inlet pipe. Pulled vacuum for 2 hours, system is extremely tight, no vacuum loss at all after 5 minutes.
Than I added 420gr r134 with the engine running and A/C "off". At 420gr I switched on the A/C as described in the manual and added another 420gr to reach 840gr as suggested by Thomas.
Operation worked perfectly well, but: the A/C doesn't cool. Compressor cycles on and off as it should but air temperature at outlets is merely colder as outside temp.
Every time the system activated the compressor the engine RPM drop significantly, at a point the engine even stopped. So the compressor runs very sluggish.

I checked the refrigerant hoses:
- hight pressure line is hot at the compressor
- Low pressure line is NOT cool after condenser (as I'd expect it to be)

No error codes in the A/C diagnose function.

Any guess what might wrong? I don't know whether or not the A/C was operative before as European customs require all R12 refrigerant to be drawn and recycled for newly imported cars. So maybe the orifice is stuck?
What can I test now? I'm terribly lost when it comes to A/C stuff...

[jss06c6]

Did you change the orifice tube?? Mine had contamination and some metal shavings in it.

What are your high and low side pressures and what is your ambient temp when you capture these pressures?

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[Matt B]

Orifice no. I have a spare on hand so maybe that's the next step. I wanted to avoid swapping out any parts and keep it simple - didn't work
I didn't measure the pressures. Where do I take them? Low side at the accumulator/dryer, high side on the line next to the right front wheel?

I'll do more troubleshooting tomorrow. Really strange that it doesn't cool at all...

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[mhobtr]

Did you drain all of the old oil from the system?

[1991 Corvette ZR-1]

Good thread. Glad this was brought back up as my AC is basically blowing room temp and during the hotter months, I only drive it in the early hours of the morning here in sunny Florida. Not sure if the conversion has been done on my 91 but the condenser is in rough shape. I think this might be a winter project for me. A complete overhaul and replacement of everything possible. Looks like I have some reading and researching to do.

[jss06c6]

Originally Posted by Matt B

Orifice no. I have a spare on hand so maybe that's the next step. I wanted to avoid swapping out any parts and keep it simple - didn't work
I didn't measure the pressures. Where do I take them? Low side at the accumulator/dryer, high side on the line next to the right front wheel?

I'll do more troubleshooting tomorrow. Really strange that it doesn't cool at all...

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Yes on location of low and high pressure valves.

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[Matt B]

Thanks, I'll try to measure later today.

Originally Posted by mhobtr

Did you drain all of the old oil from the system?

Not all, just from the compressor and whatever was trapped in the old dryer. Then added oil as instructed by the manual.
Would excessive oil lead to a complete failure of the cooling performance?

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[Matt B]

One more thing, maybe it's an indication... When I got the car all R12 has been removed during import. As expected the compressor didn't run as low freon was detected. However, even at that time no "low freon detected" code was present und the A/C controller diagnostic mode. No idea why the compressor was shut off though no error war present.
It started running as soon as fresh r134 was charged.

I'll try to apply the error procedures outlined in the manual later today, yesterday I was trapped at home by a massive thunderstorm...

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