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How many lbs. of r-12 should be in a 1987 rd686sx.   The sticker on my 1995 rd688 says 3lbs  but that is r134a. no sticker to be found on the 87

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well, i put 2 lbs of r12 in since i couldn't find an answer.   stays around 35 psi on the low side gauge... i'll run it for awhile and see if it is satisfactory.

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That’s probably close, I do HVAC for a living but don’t mess around with automotive stuff very much. The couple of R-12 I’ve messed with ran around there.  Overcharging is worse than undercharging so best bet to play it safe.  I find the trucks more difficult to charge by feel if you can’t get the clutch fan to stay engaged.  Andy

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Well the tag on the 05 granite says 3lbs of the new stuff if that helps ya 

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5 hours ago, 6368 said:

well, i put 2 lbs of r12 in since i couldn't find an answer.   stays around 35 psi on the low side gauge... i'll run it for awhile and see if it is satisfactory.

I had my truck guy that is really good with A/C do mine. He vacuumed the system then added 6 oz of oil which is very important then added 2 lbs of 134r. The 134r has 2oz of oil per pound as well. We ran it and fine tuned it with the high and low pressure gages. Added another 8oz of 134r and it has been running ICE cold since.  He said that the gage pressure are the tell-tail for the right amount refrigerant. I did convert from R-12 to R-134 because of the R-12 getting real hard to come by here.

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If it’s sweating back to compressor on the suction line; most of the time it’s real close. Main thing is the high side on gauges are not too high. If charging it where no air can get to the condenceing coil then you’ll have bad readings. I always try to have in place so air can flow & have engine around 1500 rpms 

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