Evacuate and Charging Procedure.
Attach a/c manifold gauges to the vehicle. Make sure you attach the correct hose to the proper service port. This is very important to prevent personal injury! Attach center (Yellow Hose) to a UL approved a/c vacuum pump. Open both of the dials on youÃ¢ÂÂre a/c manifold gauge set. This will allow the system to be evacuated through both the low and hide side of the system. Turn your approved vacuum pump on starting the evacuation process. 30 minutes usually will be enough time. If vacuum pump has ballast read the owners manual concerning this option.
When system has achieved a state of 29.9 hgÃ¢ÂÂs of vacuum close both dials on the a/c gauge set. You may loose up to 1 hg for every 1000 feet above sea level depending on the capacity and quality of pump. At this point wait 5 to 10 minutes letting the vacuum boil off any moisture trapped in the refrigerant oil. This is also a good time to watch and see if vacuum has returned to a zero state. If so you need to check for leaks in the system. Assuming the system is holding a vacuum after letting the moisture boil off repeat the evacuation procedure again. This process may need to be done a few times before all moisture has been removed and you see no degradation in vacuum after closing both dials for 5 to 10 minutes.
With both dials closed remove the center charging hose attached to the vacuum pump and connect it to either a can tap and refrigerant or 30lbs refrigerant cylinder. Open the valve on either the can tap or 30lbs cylinder allowing refrigerant into the charging hose. With refrigerant in the charging hose slowly crack this hose at the manifold gauge bleeding off any air that may have gotten trapped when moving from the vacuum pump to the refrigerant source. Only the slightest amount of refrigerant should be released in this process so be sure to tighten the charging line quickly!
Open only the low side dial on youÃ¢ÂÂre a/c gauges allowing refrigerant to flow into the system. Again I stress the high side must be closed or you may cause personal injury to yourself or others! Start vehicle and turn on the a/c system with blower on the highest speed. In some cases if the compressor clutch has not engaged you may need to by pass the low pressure cut out/cycling switch. Refrigerant should be charged as a gas but in some cases it may be necessary to charge as a liquid. Be careful not to slug the compressor with liquid refrigerant! Charge system to OEM amounts and pressures if you are using the refrigerant the system was designed for. If vehicle is has been or is being converted start with about 60 percent of the original charging amount. After getting 60 percent of the original charge slowly add an ounce at a time until you reach the best possible vent temperature and pressure readings. If you do not know what your systems operating pressures are you can use the 2.2 x the ambient temperature as a guide. This should only be used as a guide as many systems will need more or less refrigerant to achieve proper cooling.
Having a weak fan clutch or an inoperative electric fan will cause system pressures to be incorrect. So make sure these components are working correctly before charging a system!
In lower ambient climates, doors and or windows of the vehicle maybe required to be open to achieve proper cooling when charging the a/c system.
Automotive A/C Refrigerant Gauge Sets
i would not evac through the vacuum pump (if the vac is not meant for recovery, etc). better off getting a large empty r22 bottle, like a 30lb'er, evac the empty bottle and then hook bottle to the fridge line of manifold, then allow bottle to suck out the old stuff from the low side port.
as for inHg you get on manifold, 29.9inHg is only at sea level, at elevation this # will be different (you cant get 29.9inHg at say 3k ft above sea level, etc). i am not even sure consumer grade vac's will get you to within 0.02inHg
also, very important 1st step, zero out the dial gauges if dial is what you have. only a good digital micron gauge will tell you how close to zero (baro - vacuum) you are, etc.
another tip, most systems specify the amount of R to use, so pressures are not so important for filling. pressures are however very good for troubleshooting the system.
Edited: Fri August 15, 2014 at 10:32 AM by rstarr
Two different procedures. A vacuum pump is used for evacuation and a recovery machine is used for recovering refrigerant. Neither one need the other.
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