QuestionI have a 97 Tahoe and tried to recharge the AC unit with freon and the compressor cycles on and off not allowing the freon to pass through the system. Do I need to Evacuate the system to pull the freon through? If so, how? What are your suggestions to this problem. Thanks!
AnswerIn order to properly charge your system, you should always evacuate the system after you recover the old refrigerant. This does several things. By hooking up a vacuum pump to the system and pulling the system into a vacuum you are removing any moisture and air (non-condensable gasses) that may have gotten into the system while it was open to the environment. These non condensable gases can cause problems later dow the road. Your high side pressures reading too high will be one of them. But pulling the system into a vaccum also allows the system to be charged as a liquid much easier. The difference in pressure between your refrigerant bottle and the negative pressure inside the system will lterally suck the refrigerant into the system. Dependant upon how long the system was open to the environment will determine how long to leave the vaccuum pump pulling on the system. Generally 30 minutes is my starting point and increasing it from there. Once the vaccuum is on the system, and your ready to charge, look at the label under your hood, find out how much refrigerant your system requires, for a tahoe, I anticipate around 2.5 pounds. Place your refrigerant bottle on a scale, and charge it as a liquid into your HIGH side until your scale indicates the proper amount was charged into it.
>>>> The reason your compressor is cycling on/off is because your low pressure switch is cutting it off due to not enough refrigerant system being in the system to keep it closed. If you do not have a vacuum pump and want to continue going the way you are, you can disconnect your low pressure switch and jump the connections in the harness to keep your compressor running while you are charging the system. This will allow the compressor to continue pulling the refrigerant into the system without the cycling. But MAKE CERTAIN you reconnect it when you are finished. This is a vital safety component for your system.
>>>> Your low pressure switch is generally located on your accumulator. The accumulator is an aluminum "can" with two lines connected to the top of it. Roughly the same girth as a soda can, but stands taller. If it is not there, trace your low side lines until you find it.
My recommendation is of course to use a vacuum pump, but it can be done either way.
I hope this information helps, if you need more please feel free to ask.
