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  #1  
Old 08-12-2010, 02:45 PM
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Pressure after Conversion R12 to 134A

I have searched and found some very good articles here on the A/C systems.
After some research I found that my car was already converted. It was low on 134A I added some but it is not very cool at all and the aux fan is not coming on ( am going out in a minute to troubleshoot it) Any way this car does not have label indicating it was converted so I do not know what the proper charge pressure should be on the low and high side. Any guideline such as if your R12 pressure was this you should have this after the conversion. I should add this is on the 85 300SD.
Thanks
Alan
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  #2  
Old 08-12-2010, 03:09 PM
LarryBible
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Without having the history of the car, there is no way to know if it is 134 without connecting a Refrigerant Identifier. There are so many Yahoo's out there putting everything under the Sun in cars these days, that there is just no way of knowing.

The best way is to charge by weight, beginning with 70% of the specified R12 weight in 134 into an empty, evacuated system. Failing that, with 134, shoot for a high side of about 2.2 times ambient temp with engine at a fast idle, a/c turned on wide open and a supplemental fan blowing at the condensor.

Hope this helps,
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  #3  
Old 08-12-2010, 03:27 PM
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Larry, Thanks that does help. I did have it checked at a local shop but I did not want them to do anything else so he was not real happy. Anyway I then cam home and using a small can of 134 w/ a built in gauge put some but not all in just trying to see if the compressor would come on and it did without taking an entire can and it has held pressure
over night. I was about to put my gauges back on it and see what the pressure was on both sides as well as trouble shooting the aux fan. The fan has not come on at all even with the a/c at max. I know I am jumping ahead and should take care of the correct amount of 134 first but until I can hook up with my friend and use his recycler and vac pump I want to keep busy on other things ( I hope my new fuel lines come today)
Is the pressure compared to temp also valid. I know that my Bud ( an HVAC tech) always uses the scale before he begins.
Thanks
Alan
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Old 08-12-2010, 04:21 PM
LarryBible
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Don't worry about the aux fan yet. It is usually actuated by excessive high side pressure and you haven't gotten to that point yet. Check the charge with gauges as I described.
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  #5  
Old 08-12-2010, 04:43 PM
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R134 is a junk refrigerant. You'll never get properly cold air out of it. Have the shop put a vacuum on it and refill it with duracool.
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  #6  
Old 08-12-2010, 04:44 PM
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Again Larry, Thanks. I have not worked on any A/C in about 10 years since a friend owned a shop and owed me money. I had to run around and remember which friend borrowed what tool so I could get them back. I had to side line my car hobby for a while but I am back in the fun again. Anyway I found some references for pressure versus temp but yes I will do it correctly via weight.
At first I thought this conversion was done at the Stealership ( My Dad loved to make a day of it drive from VA up to Bethesda MD where he bought it and leave the car and the 2 of us would grab lunch and maybe hit a bucket of golf balls) But I believe he started using a very good shop in the mid to late 90's .
After I posted last I went out and put the gauges on again and as I pulled them off ( Major thunder/rain storm rolls through) the shut off pin in the center of the low side connector stuck a little and lost gas for 2-3 seconds until I used a steel punch just to reset it. That little bit of gas lost and then the compressor would not engage. I have put over $500. in maint in the last 60 days just bringing necessary items up to spec as well as for a baseline going forward so I am hoping all is well with the A/C other than flush, and fill.
Also the USPS just dropped of my full Viton fuel line set so I can start on that when the rain lets up. God I wish I had rolled the 911 and the 500E into the driveway before I started this.
Thanks
Alan
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  #7  
Old 08-12-2010, 11:00 PM
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Take a look here: http://www.ackits.com/aacf/ptchart.cfm
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  #8  
Old 08-13-2010, 09:10 AM
LarryBible
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What were your pressure readings before you pulled off the gauges? If it a few seconds of refrigerant escape tripped the low pressure switch, the readings probably weren't worth reporting.

If you could find a shop with a refrigerant identifier and confirm what refrigerant is contained therein, you may be able to proceed by simply topping it off if you can't find any leaks. In your climate, 134 might very well get the job done. If not, you can flush and reverse convert to R12.
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