AC recharge.. How long to pull vacuum?
09-03-2007, 07:41 PM
#16
Burning Brakes
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I can depress the high side port with a screwdriver and get a little hiss that is all...
Later I will check to see if the gauges have moved....
I get someting like 50 pounds until the compressor kicks in then it drops to 30... the high side needle goes down from like one or two psi to zero when the compressor kicks on....
But that only happens when I short the contacts on the switch....
When I first put the freon in the gauge would bounce from 30-40 even with the compressor off.... Weird....
JC
09-03-2007, 08:33 PM
#17
Three Wheelin'
The needle bounce is normally the charge equalizing and expanding. You most definitely have a blockage somewhere. How long did you pull vacuum and did you pull both sides or just one? Did you you a micron gauge to determine how low you pulled the vacuum? How long did you wait before charging?
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Darryl Pirtle (08-10-2019)
09-04-2007, 12:12 AM
#18
Burning Brakes
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I have an older R12 gauge set. I pulled vacuum for about 2 hours... and I left both valves open... when I close the high side valve I get a good 27-30 vacuum but when I leave the high side open I only get 10.
Tonight when I got back from a meeting I saw the pressure was down to 20 psi on the low side...
So I got a leak and probably a plugged up receiver dryer... I have a couple of used ones laying around so I will try to replace the seals and put another one in and try the whole thing again....
Tonight when I got back from a meeting I saw the pressure was down to 20 psi on the low side...
So I got a leak and probably a plugged up receiver dryer... I have a couple of used ones laying around so I will try to replace the seals and put another one in and try the whole thing again....
09-04-2007, 08:26 AM
#19
Three Wheelin'
Last time i check a receiver dryer wasn't but $20-$30 you may as well replace it with a new one and while the lines are open purge the system with dry nitrogen or if you must compressed air.
09-04-2007, 08:47 AM
#20
Burning Brakes
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I will check on the price of a new one... I just never put porsche and affordable in the same sentence usually LOL....
I am beginning to think the compressor may be bad too... but swapping out the dryer "looks" easy enough to test it out...
JC
I am beginning to think the compressor may be bad too... but swapping out the dryer "looks" easy enough to test it out...
JC
09-04-2007, 04:41 PM
#21
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A couple comments- hopefully useful and relatively accurate.
Pulling vacuum isn't the best way to check for leaks. 30 inches of mercury is about 15 psi, 750 mm of mercury (mm Hg) or 1 Bar. R12 134a vapor pressure at normal temperatures is much higher. A leak detectable using vacuum would hiss audibly and empty the system in a few minutes tops.
The high and low pressure sides aren't separate. Vacuum pulled at one port will pull down everthing. If you are pulling 30 inches low side and opening the high valve drops you to ten, your test guage system is leaking, not the AC.
Longer vacuum removes more volatile residue. In A/C, the volatile residue of interest is water. Change your accumulator/dessication cannister. A new one can trap more water than you can remove by extending vacuum time beyond a few minutes.
Hope this helps.
Bill
Pulling vacuum isn't the best way to check for leaks. 30 inches of mercury is about 15 psi, 750 mm of mercury (mm Hg) or 1 Bar. R12 134a vapor pressure at normal temperatures is much higher. A leak detectable using vacuum would hiss audibly and empty the system in a few minutes tops.
The high and low pressure sides aren't separate. Vacuum pulled at one port will pull down everthing. If you are pulling 30 inches low side and opening the high valve drops you to ten, your test guage system is leaking, not the AC.
Longer vacuum removes more volatile residue. In A/C, the volatile residue of interest is water. Change your accumulator/dessication cannister. A new one can trap more water than you can remove by extending vacuum time beyond a few minutes.
Hope this helps.
Bill
09-05-2007, 12:21 AM
#22
Burning Brakes
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A couple comments- hopefully useful and relatively accurate.
Pulling vacuum isn't the best way to check for leaks. 30 inches of mercury is about 15 psi, 750 mm of mercury (mm Hg) or 1 Bar. R12 134a vapor pressure at normal temperatures is much higher. A leak detectable using vacuum would hiss audibly and empty the system in a few minutes tops.
The high and low pressure sides aren't separate. Vacuum pulled at one port will pull down everthing. If you are pulling 30 inches low side and opening the high valve drops you to ten, your test guage system is leaking, not the AC.
Longer vacuum removes more volatile residue. In A/C, the volatile residue of interest is water. Change your accumulator/dessication cannister. A new one can trap more water than you can remove by extending vacuum time beyond a few minutes.
Hope this helps.
Bill
Pulling vacuum isn't the best way to check for leaks. 30 inches of mercury is about 15 psi, 750 mm of mercury (mm Hg) or 1 Bar. R12 134a vapor pressure at normal temperatures is much higher. A leak detectable using vacuum would hiss audibly and empty the system in a few minutes tops.
The high and low pressure sides aren't separate. Vacuum pulled at one port will pull down everthing. If you are pulling 30 inches low side and opening the high valve drops you to ten, your test guage system is leaking, not the AC.
Longer vacuum removes more volatile residue. In A/C, the volatile residue of interest is water. Change your accumulator/dessication cannister. A new one can trap more water than you can remove by extending vacuum time beyond a few minutes.
Hope this helps.
Bill
Cool... but when I attach the vacuum and only open the low side valve I get 27 inches almost immediatly.... Maybe I have a stuck or clogged shrader valve...
I ordered a new dryer and tube so when they get here I will install them and try a different set of gauges...
Thanks for your advice JC
