A/C Charge

[tdangle]

I discovered a loose connection on my AC system and resulting leak. I need to recharge and am a little unclear on which pressure chart (low side) to use. R12 or R134. this is a totally stock system with recalibrated POA valve. When I filled the system 2 years ago, I just went by 80% of total volume as per the R134 conversion charts. Yes I changed the oil out to ester oil as it was compatible with both freons and if a residual amount of mineral oil remained. It has worked OK for 2 years.

Should I shoot for 40 to 50 at 80 degrees or 25-36 at 80?

Right now I put 1 12 oz can in and is right at 30 at not quite 80 degrees and center vent temp is 50 degrees.

[weq92f]

Originally Posted by tdangle

I discovered a loose connection on my AC system and resulting leak. I need to recharge and am a little unclear on which pressure chart (low side) to use. R12 or R134. this is a totally stock system with recalibrated POA valve. When I filled the system 2 years ago, I just went by 80% of total volume as per the R134 conversion charts. Yes I changed the oil out to ester oil as it was compatible with both freons and if a residual amount of mineral oil remained. It has worked OK for 2 years.

Should I shoot for 40 to 50 at 80 degrees or 25-36 at 80?

Right now I put 1 12 oz can in and is right at 30 at not quite 80 degrees and center vent temp is 50 degrees.

I fly by the seat of my pants when it comes to A/C charging! So far so good...

50 at the vent doesn't sound cold enough, but at 80 ambient that's 30 degrees difference, so by that standard it is cold enough. If it were me I'd be adding slowly until I got down near 40 then call it done. I've currently got VA system and this is how I charge it. Usually it's about 18-20 oz total. If I recall correctly the low pressure was around 40.

Hth,

-klb

[Davidf]

...or just add 80% of required R-12 weight volume. I cannot remember the R-12 weight volume...3.25 lbs. If so, then start at 2.6lbs of R-134a

[Wrenchbender Ret]

If you have a sight glass, charge it till the foam dissapears. The sight glass is on the top of the receiver/drier.
George

[Davidf]

Originally Posted by Wrenchbender Ret

If you have a sight glass, charge it till the foam dissapears. The sight glass is on the top of the receiver/drier.
George

I do not think that works with R-134a.

[tdangle]

I agree, everything I read about the sight glass is it doesn't work correctly with R134a. I'll try bumping the low side up to about 35 at 80 degrees and see what the vent temp is. In my researching it does seem as though there is no hard fast rule about pressures with the conversions. I don't know the total charge since part of the last full charge leaked and I don't want to just bleed it down to nothing to bring it back up, not to mention your not suppose to vent the gas into the atmosphere. Trying to be responsible.

[Stocker]

Originally Posted by weq92f

50 at the vent doesn't sound cold enough, but at 80 ambient that's 30 degrees difference, so by that standard it is cold enough.

When I was resurrecting my A/C a few years ago, a mechanic told me that a 30 degree reduction (from ambient to the vents) was acceptable.
We can see 110 degrees here at times -- did he think 80 degrees at the vents was cold enough? Well, no..... neither one of us thought so.

[body bolt]

Originally Posted by tdangle

I agree, everything I read about the sight glass is it doesn't work correctly with R134a. I'll try bumping the low side up to about 35 at 80 degrees and see what the vent temp is. In my researching it does seem as though there is no hard fast rule about pressures with the conversions. I don't know the total charge since part of the last full charge leaked and I don't want to just bleed it down to nothing to bring it back up, not to mention your not suppose to vent the gas into the atmosphere. Trying to be responsible.

Yeah, with POA you can't go by pressure. I hung on to the evaporator discharge till I felt it was cold enough. Very scientific ... If you have a scale you could charge to 70-80% of the R-12 charge which is 3.25lb.

[tdangle]

Originally Posted by body bolt

Yeah, with POA you can't go by pressure. I hung on to the evaporator discharge till I felt it was cold enough. Very scientific ... If you have a scale you could charge to 70-80% of the R-12 charge which is 3.25lb.

Did not realize that you can't go by pressure on the low side with a POA system. I just confirmed it myself. Just added a little bit until the vent temp wouldn't go any lower and called it a day. Right at 80 outside and got about 45 vent temp. High side was a tad over 200, but low side was 27-28

[Davidf]

Originally Posted by tdangle

Did not realize that you can't go by pressure on the low side with a POA system. I just confirmed it myself. Just added a little bit until the vent temp wouldn't go any lower and called it a day. Right at 80 outside and got about 45 vent temp. High side was a tad over 200, but low side was 27-28

Your in the range. You do not need a scale to get close on volume. 80% of 3.25 lbs is 2.60 lbs. 16 ounces in a pound so need to add 42 ounces to the empty system. Most R-134a cans are 12 oz. Divide 42 by 12 to get 3.5 cans of 12oz R-134a refrigerant. If you want it exact, put a full 12oz can which is connected to the refrigerant gauges on a postal scale. Note the weight. Stop filling the system when the last can weighs 6oz less than when you started.

[body bolt]

Originally Posted by Davidf

You do not need a scale to get close on volume. 80% of 3.25 lbs is 2.60 lbs.

I charge from a 30lb bottle.

[Davidf]

Originally Posted by body bolt

I charge from a 30lb bottle.

Welp, then you need a scale, wing it, or buy four 12 oz cans.