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How much freon?

How much freon?

How much freon?

Can anyone tell me how to determin the amount of freon (134) is required in an automotive a/c system? I have installed a roof top a/c on a tractor and have no idea how much freon to put in.

RE: How much freon?

Usually the unit shows the amount and pressures.

Be careful

RE: How much freon?

Yeah thats my problem...I need to determine how much R134a it holds so I can have a decal made to put on the machine! I work in an R&D shop. We built this machine and installed the A/C. I haven't had much A/C experience, and I'm having trouble finding information about determining the refridgerent capacity.

RE: How much freon?

To start, find a technician that has the proper test equipment and he can simply charge the system to normal operating parameters. Then measure/weigh the amt you used.  Simple.  It really is not rocket science.  You can do it yourself if you buy the test equipment and pull up one of the DIY sites with video...Then just 'follow the bouncing ball' !!!


RE: How much freon?

You also need to get the initial charge of (special! magic! refrigerant compatible!) lube oil right, so the compressor oil level will be about right even with a few ounces of lube oil circulating through the system with the refrigerant.  ... and occasionally you have to add bypass lines to make the oil flow around natural/inadvertent traps.

If you don't feel comfortable, consider farming out the job.


Mike Halloran
Pembroke Pines, FL, USA

RE: How much freon?

Thanks for the help! We have a new Robinair charging station, and we did the initial charge at the recomended 2 pounds. The A/C seems to work very well. I just wanted to try to figure out what the exact amount of refridgerent should be before I committed to a decal order!!

RE: How much freon?

You can try vapor charging a little more at a time while watching the evaporator air temperature.  From a slightly undercharged state, the temperature should fall, then start to rise.  I stop adding refrigerant when it's risen about 1...2 degF.  I don't know if that's really an optimum, but it works okay in the backyard.

OR you can try measuring temperatures and pressures and calculating the superheat and subcool temperatures, as the refrigerant manufacturers recommend.  I've tried it on occasion, but never trusted the numbers because I couldn't get temperature readings that I thought represented the temperature of the refrigerant, by measuring the exterior of various tubes or fittings, and I wasn't prepared to open the system to install temperature probes.


Mike Halloran
Pembroke Pines, FL, USA

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