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Canmore Ab. Canada | I am an amateur at this so please be patient with me.
If the system read zero when you put your guage on it probably should have been evacuated with an a/c vacuum pump before charging. You could then see if it would hold a vacuum or if there was a major leak. If there was a major leak it could be repaired and the dessicant/ filter should be changed. The system would have to be vacuumed before charging.
I am a farmer and if it is impractical to evacuate the system and you need to go, sweep a small amount of refrigerant throught the system by puttin it in the low side untill you have positive pressure on the high side and the close the lowside valve and release the pressure through the high side valve. It is not a vacuum job but will chase the majority of the air/moisture through the system. Yes you do need a good set of guages or it's kind of a shot in the dark.
Air is a contaminant that can cause increased high side pressures, makes your system work harder, and moisture is bad like sand in a motor. Depending on your refrigerant and oil it can cause acid to be formed which will eat away at your system from inside out.
Depending on your system and refrigerant the normal system pressure with nothing turned on should be approximately the same as the temprature of the ambient air in degrees farenheit IF THERE IS LIQUID PRESENT in the system. Lower than that, give or take a bit, the system is basically empty. If you have appropriate pressure there is liquid present and you will not know how much without further tests. It could, and most likely is low if the system does not work properly, it could be correct or even overcharged in some cases.
The high side pressure will probably run in the neighborhood of two times ambient air temprature in degrees farenheit. This also depends on the refrigerant. New refrigerants seem to be a bit lower.
As Jon said the hissing could be the normal sounds of an expansion valve or orifice tube system. Try locate the leak with soap water if you can get at it. It is also possible you added enough refrigerant to just get the system cycling and it is the small amount racing around. The rapid cycling would lead me to believe you are low on refrigerant yet.
If the system was empty, and by your pressure, 0, it was, you should then be able to charge by the required amount by the sticker or book. Keep in mind if your are changing refrigerants ratois may vary. An old R12 system for example may call for 3 lbs where as 134a will take about 2.7 lbs and if you use a produce such as Redtek 12 you will only need about 1 lb.
If you feel you have a minor leak I would suggest a stopleak product compatible with the refrigerant you are using and see if that works prior to major repairs.
Best of luck.
Dan... | |
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Freightliner A/C diagnosis
