Your compressor does not stay running longer because you are very low on freon. There should be a tag that tells you how much the system will hold, probably at least 3 cans. The system is pulled to vacuum not to get the freon into the system but to remove moisture from the system. Moisture in the system will freeze and interfere with operation. You have a low pressure switch to cut off the compressor in the event the freon level gets too low. The rapid cycling happens because the pressure is low enough that the compressor rapidly pulls the suction pressure down enough to cut off the compressor.
The system is pulled to vacuum so the boiling point of any moisture present drops low enough that it actually boils off and is removed. The system is then held at a vacuum for a period to be sure that the moisture is removed and the system does not leak. Then freon is introduced, the vacuum does aid in getting the first small amount in, but after that the compressor pulls the freon in through suction.
Air conditioning shops remove and install the freon with recovery machines. The freon is drawn out, filtered and stored. The machine is then used to pull a vacuum to remove moisture and assure integrity of the system, then it very accurately measures the freon as it pushes it back in. Without this machine the process relies on your AC compressor to pull the freon back in. The freon is drawn in, compressed and cooled to revert it back to liquid. As the level of freon in your system builds, both the suction and discharge pressure of the compressor increases. When the suction pressure reaches about 30 psi the compressor will run most of the time at idle and the system will blow cold air. When engine speed increases it may cycle on and off occasionally.
You should never drain the freon from the system by releasing it into the air! It is not necessary, it allows moisture to be introduced, and not to mention intentionally releasing freon is against the law. Suction and discharge pressure of your compressor indicates level of charge.
The system is pulled to vacuum so the boiling point of any moisture present drops low enough that it actually boils off and is removed. The system is then held at a vacuum for a period to be sure that the moisture is removed and the system does not leak. Then freon is introduced, the vacuum does aid in getting the first small amount in, but after that the compressor pulls the freon in through suction.
Air conditioning shops remove and install the freon with recovery machines. The freon is drawn out, filtered and stored. The machine is then used to pull a vacuum to remove moisture and assure integrity of the system, then it very accurately measures the freon as it pushes it back in. Without this machine the process relies on your AC compressor to pull the freon back in. The freon is drawn in, compressed and cooled to revert it back to liquid. As the level of freon in your system builds, both the suction and discharge pressure of the compressor increases. When the suction pressure reaches about 30 psi the compressor will run most of the time at idle and the system will blow cold air. When engine speed increases it may cycle on and off occasionally.
You should never drain the freon from the system by releasing it into the air! It is not necessary, it allows moisture to be introduced, and not to mention intentionally releasing freon is against the law. Suction and discharge pressure of your compressor indicates level of charge.
