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A/C low-high pressure graph
03-17-2009, 04:40 PM
I recently changed out my A/C compressor and am presently in the process of charging the system. I went to my factory manual and there is no graph showing low/high pressures by temperature. Does anyone have access to this graph? I'd like to get a copy. My factory manual refers to a supplement for this info.
03-17-2009, 10:40 PM
Why would you need that? Why don't you just put in the amount the system tells you to?
03-18-2009, 06:14 AM
I think it's just standard for the particular coolant, nothing to do with the car. Just look up the proper graph for Freon or R134a.
03-18-2009, 04:29 PM
I started with a partial can. I was not sure how much was in the can. The sticker says the system holds 1.3 lbs. That's 19.3 oz. I also was not sure if any r-134 graph would work because this system is way smaller than the average automotive system. The average system is 2-3 lbs. A system that size you would charge till the low side reads about 38 lbs. I'm presently reading 12 lbs and the low side piping is starting to sweat. By having the correct graph showing the low/high pressures according to ambient temperature then I would be sure. I really did not want to but I guess I can over charge it and let gas out until the high side safety switch stops cycling. A graph would be better though. Nobody has one?
03-18-2009, 07:26 PM
Did you vac the system at all? If there is air in there it will screw with your pressure readings not to mention the moisture trapped in there. If you charge an unknown system by feel and gauges, usually 30-40psi is a good low side number as long as it's dropping the inside temp down to 40-50F. Make sure you get enough oil in there.
03-18-2009, 08:36 PM
Yep, I pulled it down for an hour and held it for another hour to check for leaks. No problem there. I added 3 oz of ester oil for the dry compressor. I did not replace anything else because there was no failure of any of the components. The original compressor had a slight leak (top off every 6-8 weeks) and the clutch was going bad. No I did everything right. I guess i'll shoot it up some more and keep the low side pressure between 30-40 lbs.
03-21-2009, 12:02 AM
I have a 2000 Metro and have the graph in the FSM - if you still need it post back and I will put it up for viewing. Really the correct way to charge the A/C is through a manifold guage set while monitoring the high and low side pressures and also measuring the ambient and discharge temps (I use a small HVAC thermometer which is made for this purpose). You can charge it directly out of the can but the readings tell you whether the A/C is working correctly or not.
03-23-2009, 01:10 PM
You are exactly right. I have the complete gage setup. I just needed the graph. Thanks in advance for posting the graph. I really appreciate it.
03-24-2009, 12:02 AM
Okay here it is - the scan is a bit crappy but hopefully you can see it.
Also to add that in order to correctly measure the discharge temp you need to close all the windows and use recirculation mode - in other words not drawing in outside air over the evaporator.
03-25-2009, 04:27 PM
A special thanks to hot_sd for the graph I was looking for. The picture was fine. I had to go through some banter to get it but it was worth it. I finished charging this morning and everything is great. All the temps and pressures are in spec.
03-25-2009, 11:08 PM
Good to hear that. Coincidentally I need to fix the a/c on my metro - it has had a leak that has got worse over the last few years - I had to recharge every 2 years or so - but now it has got really bad where it won't hold the charge for very long. I bought the refrigerant with the UV dye to try and locate the leak and was even wondering about buying a used Halide detector on ebay but have not really bothered to fix it.
I will get around to it one of these days.......
03-26-2009, 07:38 PM
My leak was at the front seal on the compressor. I ended up changing it because my clutch was crapping out. The rebuilt compressor w/clutch was bought on EBAY for $117.00 delivered. Since there was no compressor failure I just replaced the compressor w/out the receiver dryer or orifice tube so no warrantee. They did have complete kits including all needed components and seals/o-rings for a decent price.
Thanks again for your help.
03-26-2009, 10:53 PM
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