I accidentally over charged the 95's A/C. What's the best wat to let some out without letting any oil out at the same time.

Maybe attach gauges and just crack it a little not very fast.?

I tried at the Low side Shrader Valve and got oil.?

 

Go to an AC shop and let them release it legally through their vacuum machine and set it at the proper pressure.

Supposedly freon is a nasty substance when it comes to ozone layer.......yeah...whatever....:rolleyes :

 

How did you determine that yours has too much 134A?

Jake

 

I filled it Sunday to what I thought was 40 Psi on Low side which is correct. I guess my gauge is off.It wasn't cooling well so I put on another gauge and it was like 55 Psi.

 

Only legal way is to have it done with a recovery machine. A small shop will charge little to nothing to take some of your freon (they are getting your freon free). You can get a big fine if you were to get caught hooking your manifold guage up and just open the valve a little untill you get your desired pressure. This wouldn't let enough oil out to matter.

 

Not being an A/C guy, I'm relying on what I've read on packages at the auto parts stores: The actual pressure you see on your gauge is ambient temperature dependent.

I higher the amibient temp at the time the pressure is tested, the higher the reading will be.

So, the 134A charging can which comes with a gauge and instructions , the instructions say look for something like 45 PSI but that's when the ambient temp is something like 80-85 F (I'm going from memory on this so check those numbers).

Jake

 

With vehicle on park there is no airflow flowing through the condenser, causing a higher than normal suction and head pressure. You're aiming for a 40 degree evap coil ,If you were to convert 37. 5 lbs. of pressure that would get you 40 degrees. What i do is get a pocket thermometer and put it in the center vent . I have a capet dryer that i put in front of the condenser. that seems to help, but weight method of charging is the best and most accurate way ,which means look for manufacture specs and find out how much goes in there .
but you would have to remove and vacuum system. 45 lbs is about right because once you get on the highway pressure well drop to 37.5 .

 

Usually you can't cram more than an additional couple of ounces into it - take your pressures with the engine at 1200 rpms, at least the main fan cranking. You should aim for a high side of 2.2 to 2.5 times the temp of the air across the condensor. At that high side pressure, the low should fall into place. Post pressures, outside air and center vent temp.

 

It's fixed. My A/C Guy said I hade about a half poundt oo much.

He said like todays Temp of 88-90 F in Southeast La. He says if I'm gonna add in the future fill the Low side roughly to 40-45 Psi and the High side you don't want over 200 Psi.

 

Glad you got it fixed!

40 psi is about the max low on most of the GM charts I've seened for R134, but I'd go lower. At that pressure, R134 has a saturation temp of 45 degrees. Add in 5 to 8 degrees for superheat and you evaporator has a temp of 50 and above. Depending on how efficient the plumbing is, it ends up with a 55 degree (and up) vent. I like to see no more than 35 psi (at 90) which keeps the Evaporator below 50 degrees. That may be a slight undercharge - more cycling below 60 to 70 degrees - but given your summers, I'd wouldn't worry about it.

 

Good:

So we want the Low side, @ 90 Degrees, about 35 Psi.

My A/C guy said the high side should Not exceed 200 Psi.?

Which reading should I watch..Low , High ? or Both????

and at cooler Ambient Temps, I'd need to fill closer to the 40 Psi mark?

Am I on the right track?

 

You look at both which will vary depending on the outside temperature, but knowing the saturation temperature of R134 at various pressures really helps - should be a chart on the Board at www.ackits.com - look in FAQ's. If you want to see what GM thinks the performance of your Vette should be, a Chart is included in the Field Service Manual. I like the guideline I gave you for the high - 2.2 to 2.5 times the temp of the air across the condensor (often 10 degrees higher at idle than ambient for a bottom feeder like the Vette), so if it's 90 degrees, a high side in the area of 200 to 225 psi is a good average number. I wouldn't go below these pressures at 90, but something 10 to 15 psi higher wouldn't be unusual - systems vary from car to car - the engineering is close, but not precise. Also, most of the GM charts I've seen allow for much higher pressures - often in the 300's at this temp - but those are maximum numbers and it doesn't mean that you can't make it better. You should also check the operation of the fans and for an R134 car, they're generally cranking below 200 psi - exact specs will be in the FSM and you'll need a scanner to verify that it's working right (something a lot of a/c shops don't have).

Design is to meter liquid into the Evaporator at a saturation temp of 25 degrees (22 psi) to 45 degrees (40 psi) under most conditions (generally below 95 degrees). After the liquid boils, sensible heat is added - superheat - which keeps the gas from condensing back into a liquid and the Evaporator from icing up when the saturation temp is below freezing. That's usually 8 degrees to 10 degrees. If you take the temperature at the Evaporator outlet, you'll get a good idea as to what it is and the actual temp of the Evaporator. Too much superheat is usually a low charge, but it can be host of other things and automotive guys just look at pressures and take it from there.

 

Thanx Guys...Lot's of useful info.

OK It's full,2 Lbs. of 134A. Road Tested. Approx 89F yesterday and the center vent temp pulled down to 57-58F in city driving and only for about 10-15 Minutes, I imagine longer on the Highway,it would have pulled down further.I think a Delta "T" of 32 Degrees or so isn't bad?

What do you think?

I'm gonna take the Static and Running pressures and Log them for next time.

 

That's a great temp differential, but if it's on recirc, you need to look at the inside not outside temp. More than likely, after it's stabilized, it's a 20 to 25 degree difference.

 

You mean the Air at the Vent Temp or Inside Cabin Temp?

 

Inside Cabin Temp at the recirc door - passenger side right side cowl. On MAX, it shuts off most of the outside air (some still flows for safety) so that only cooled air is sent to the Evaporator. Your home unit works the same way only short of opening up the windows or doors, the unit is always sucking inside cool air from the Return.