Full charge after only half the freon?

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Cusser
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Re: Full charge after only half the freon?

Postby Cusser » Tue Sep 01, 2020 1:26 pm

JohnHere wrote:About 30 ounces of R-134a does seem a little light. I think it should be around 32-38 ounces based on the R-12 spec. Did you weigh-in the charge or estimate using the small cans? If the latter, it's possible that you charged more than you thought. The pressures look pretty good now. What are the vent temps?


I think that you are low on R134a as well. My math says more like 43 oz. R134a. And you'll never get full 12 oz. from a can with line purging and some remaining in the can, so figure at best 11 oz. per can. Mist the condenser, run a fan over the condenser if necessary to add the correct amount.
kenneyd
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Joined: Tue Sep 01, 2020 4:28 am

Re: Full charge after only half the freon?

Postby kenneyd » Tue Sep 01, 2020 1:34 pm

Cusser wrote:
JohnHere wrote:About 30 ounces of R-134a does seem a little light. I think it should be around 32-38 ounces based on the R-12 spec. Did you weigh-in the charge or estimate using the small cans? If the latter, it's possible that you charged more than you thought. The pressures look pretty good now. What are the vent temps?


I think that you are low on R134a as well. My math says more like 43 oz. R134a. And you'll never get full 12 oz. from a can with line purging and some remaining in the can, so figure at best 11 oz. per can. Mist the condenser, run a fan over the condenser if necessary to add the correct amount.


I guess that's the main reason why I'm posting here, should I try to error on the side of the correct amount of refrigerant, or the correct pressures?
What if adding another 10 oz of refrigerant makes the pressures high like they were when the first compressor failed?
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JohnHere
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Re: Full charge after only half the freon?

Postby JohnHere » Tue Sep 01, 2020 2:37 pm

Conversions from R-12 to R-134a can be very tricky. You could start by adding refrigerant in small amounts (an ounce or two) while watching the pressures and vent temp. An additional person would be very helpful with this process. If the pressures start going up, along with the vent temp, you can be pretty sure that you have reached or slightly exceeded the optimum refrigerant level, and to stop there. You could even reduce the refrigerant at this point a little bit, maybe by an ounce, and call it a day.

Most occasional A/C techs can't afford the thousands of dollars an RRR machine would cost. But if you plan to continue working on MVAC, and assuming you don't have one, I suggest investing in a high-quality refrigerant scale, which will allow you to charge precise amounts of pure refrigerant from a 30-pound canister...much easier than trying to accurately charge from multiple 12-ounce cans. Speaking of the small cans, some of them might also contain sealers, which you definitely don't want to introduce into any MVAC system.

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