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Digital Scale setting for 28oz factory charge

rjpeek on Sun June 12, 2011 8:27 PM User is offline

Year: 1997
Make: Plymouth
Model: Neon
Engine Size: 2.0
Country of Origin: United States

I have a 1997 Plymouth Neon that I recently charged using a bulk container and a digital scale. The factory charge is 28oz of R-134A. I first pulled a deep vacuum and then I set the scale to 28oz. With the engine OFF and the container in the UP position I opened both valves (Low/High) to start the charge. When the pressures equalized I closed both valves, started the engine and let it run for about 5 minutes, opened only the Low side to complete the charge. Just before charging is completed, a short alarm sounds from my scale to allowing me time to turn off the supply (the bulk container). When charging is completed the scale will sound an alarm again. At that time I close the Low side, turn the engine off and remove the hoses from the A/C System.

I live in Texas and it gets very hot during the summer. Last month when the temperatures were 80-85 and below it would take about 10-15 minutes to get down to 45-50F degrees, coming out of the center vents with the blower on high. This month it takes about 20 minutes to get down to 45-50F degrees when the outside temperatures reach 100F degrees. If the outside temperature is over 100F degrees it takes even longer.

I’m starting to think that I’m not adding enough refrigerant when charging my A/C System. When charging an A/C System using a scale do you add a few extra ounces of refrigerant to the Factory Charge? For example, if I’m using a gauge set with 6’ hoses do I add 1.5oz for the Low side and 1.5oz for the High side to the Factory Charge (1.5oz + 1.5oz + 28.0oz = 31oz), then set my scale to 31oz.

My Equipment:

Robinair R-134A Gauge Set with 6’ hoses (13136)
Robinair CoolTech 4 CFM Two Stage Vacuum Pump (15434)
Mastercool Accu-Charge II Digital Scale (98210-A)

tomw on Mon June 13, 2011 3:29 PM User is offlineView users profile

When you remove the low (and high) side hoses from the system, are they not still filled with refrigerant? You don't dump it to atmosphere, so it has to be somewhere? Why not still in the hose? I would think the hoses are full of gas which would weigh close to nothing at 100F. The pressure of one drop of liquid R134a, inserted into the hoses under a vacuum, when raised to 100F would be the same as 50 drops of R134a in the same hose when at 100F. Or however many drops you can fit in with just enough room to form some gas. The boiling point is the boiling point, no matter how much liquid there was in there to start. If you are filling with gas only[right side up] you never get any liquid in the lineset.

simplificate and add lightness

chris142 on Tue June 14, 2011 12:11 AM User is offline

Fill to spec on the sticker. No more or less. Your 28oz = 1.75 lbs or 1lb 12oz.

mk378 on Tue June 14, 2011 7:56 AM User is offline

Don't close any valves until after the full charge is in. The first beep is just to warn you to be ready for the final one.

Disconnect the manifold from the car in this sequence to get any remaining liquid refrigerant out of the hoses and into the car. Close the cylinder valve. Isolate and/or disconnect the high side coupler from the service port. Open the high side handwheel valve, then slowly open the low side. This will put the gauges and all the hoses at low side pressure and the compressor will evaporate and pull the liquid refrigerant out, leaving only a tiny amount of gas that is not enough to worry about. Close both handwheels then disconnect the low side coupler.

rjpeek on Tue June 14, 2011 9:34 PM User is offline

Thanks mk378, this is the missing information that I've been looking for that makes since. One thing I think you might have forgot to mention was to turn the engine off before isolating and/or disconnecting the High Side Coupler. After the High Side Coupler is isolated/disconnected, turn the engine back on and wait a few minutes for the system to re-stabilize, then open the Low side valve, this will pull the liquid refrigerant from the high side hose to the low side hose into a/c system.

rjpeek on Tue June 14, 2011 9:49 PM User is offline

One other thing, what is the correct amount of refrigerant? My manual says 28oz or 1.57lbs but chris142 says 28oz = 1.75lbs. Does my manual have a typo? What is the correct amount for a 1997 Plymouth Neon 2.0 with Dual Overhead Cams?

TRB on Wed June 15, 2011 12:03 AM User is offlineView users profile

Mitchell states 28 ounces.

28 ounce = 1.75 lb, lbs


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