yorxs Posted April 27, 2011 Report Share Posted April 27, 2011 Hi Guys, I want to check if my air conditioning needs a topping off, it blows cold but not as cold as it should be. Its a 1993 GTP with the 3.4L running r12. I have an r12 manifold guage set and a bulk cylinder of r12 but I do not know where the needle should read to indicate a correct charge. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted April 27, 2011 Report Share Posted April 27, 2011 I want to to say under normal operating conditions you should be seeing around ~35psi Low side, ~150psi High side when running and when off it should eventually ballance to about 90-100psi on both hi and low side. Those are figures using 134a but I'd imagine they are similar Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 28, 2011 Report Share Posted April 28, 2011 STOP. FIND THE LEAK FIRST. Evacuate, FIX THE LEAK. Probably replace all the O-rings and the dessicant while you're in there. THEN, recharge. How much pressure depends on what the temperature is. Hotter day--higher pressure. Alternative = thermometer in the duct, blower on high, MAX A/C, engine at fast idle. Charge until the thermometer gets to the coldest reading, and then add an additional quarter-pound. Quote Link to comment Share on other sites More sharing options...
white4d96 Posted April 28, 2011 Report Share Posted April 28, 2011 Evacuate system Fix leak Convert to r134a ?????? PROFIT! Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 28, 2011 Report Share Posted April 28, 2011 I have an r12 manifold guage set and a bulk cylinder of r12 but I do not know where the needle should read to indicate a correct charge. Evacuate systemFix leak Convert to r134a ?????? PROFIT! I don't understand. If the guy has the R-12 gauge set, AND a keg of R12, why should he convert to 134a? Quote Link to comment Share on other sites More sharing options...
mrl390 Posted April 28, 2011 Report Share Posted April 28, 2011 x2 Thats like draining 93 octane out of your gas tank to replace it with 86. Quote Link to comment Share on other sites More sharing options...
Garrett Powered Posted April 28, 2011 Report Share Posted April 28, 2011 because he should profit and sell me the r-12? next time I go to mexico I will be looking for some of it. and some cuban rum... Quote Link to comment Share on other sites More sharing options...
alec_b Posted April 29, 2011 Report Share Posted April 29, 2011 If it's still blowing somewhat cold then the leak is probably small. 35 psi on the low side 150 on the high is right about where you want to be. Quote Link to comment Share on other sites More sharing options...
55trucker Posted April 29, 2011 Report Share Posted April 29, 2011 Hi Guys, I want to check if my air conditioning needs a topping off, it blows cold but not as cold as it should be. Its a 1993 GTP with the 3.4L running r12. I have an r12 manifold guage set and a bulk cylinder of r12 but I do not know where the needle should read to indicate a correct charge. If memory serves it should be 2 1/4lbs. (36oz. R12).....refrigerant is installed by weight, not according to where the needles on the low/high manifolds gauges read. There is no accurate way to *partially* fill a system. The proper method is to evacuate any refrigerant that is in the system so the system is at *0*and then draw a vacuum on the system to test for leaks and then to pressurize the system according to the weigh scale reading that the tank is sitting on. There are other maintenance procedures to follow and parts to possibly replace as well if the system has been opened to atmosphere. Seeing as you have a tank, you need an accurate weigh scale (preferably a digital scale) for it to sit on. If you over pressurize the system it will not function properly and will not cool as it should do. Quote Link to comment Share on other sites More sharing options...
yorxs Posted April 29, 2011 Author Report Share Posted April 29, 2011 If memory serves it should be 2 1/4lbs. (36oz. R12).....refrigerant is installed by weight, not according to where the needles on the low/high manifolds gauges read. There is no accurate way to *partially* fill a system. The proper method is to evacuate any refrigerant that is in the system so the system is at *0*and then draw a vacuum on the system to test for leaks and then to pressurize the system according to the weigh scale reading that the tank is sitting on. There are other maintenance procedures to follow and parts to possibly replace as well if the system has been opened to atmosphere. Seeing as you have a tank, you need an accurate weigh scale (preferably a digital scale) for it to sit on. If you over pressurize the system it will not function properly and will not cool as it should do. Thanks for the idea, I didn't even think of weighing it. I don't want to over pressurized the system, and I can't imagine using a thermometer in the vent would be a good indicator of how full the system is. What still puzzles me is that you can buy r134a pressure guages from Autozne so you can top off without over filling. It seems to me that the same principle should apply to r12, if I knew the correct pressure I would know when to stop filling. No one seems to sell a guage similar to the r134a ones for r12 so I am stuck with this manifold set which does not indicated a normal pressure range. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 29, 2011 Report Share Posted April 29, 2011 You aren't listening. FIX THE LEAK. If there was no leak, the system wouldn't be low on refrigerant. Then re-charge. The simple, easy, brainless way is to look at the capacity sticker and add exactly that much refrigerant to a vacuumed-out system. The better way is to watch the thermometer; and add until you've achieved maximum cooling...and then add just a bit more. Quote Link to comment Share on other sites More sharing options...
Breakdown Posted April 29, 2011 Report Share Posted April 29, 2011 You aren't listening. FIX THE LEAK. If there was no leak, the system wouldn't be low on refrigerant. Then re-charge. The simple, easy, brainless way is to look at the capacity sticker and add exactly that much refrigerant to a vacuumed-out system. The better way is to watch the thermometer; and add until you've achieved maximum cooling...and then add just a bit more. I'm assuming that you can't break one of those gauges off one of those cheap refill units that they sell @ Wal-Mart. He's right. Refridgerant is like Power steering fluid. It's not burnt or consumed. I had mine recharged and it took less than two weeks before it was dead with a leak (we put dye into it to determine the location of the leak, that's something else to consider. Quote Link to comment Share on other sites More sharing options...
yorxs Posted April 29, 2011 Author Report Share Posted April 29, 2011 Ok found the answer from a local do it yourself air shop. While he did confirm using pressure was a difficult way to measure a charge due to changes in temperature. He was able to tell me that at 85 degrees the low side should read 35psi and the high side should read 160psi. He also agreed with the scale method as an effective way to measure charging an empty system. BTW the system defiantly takes 2.25 lbs. His advice is to hook it up to the guages, if the reading is at 28psi or above I should top it off as it is not unusual for the system to loose 5 to 7 psi a year with a very small leak. If below then the system is probably leaking too quickly and will just waste any freon I add to it. He also told me that it is harder to overcharge an r12 system mainly becuase r134a only works effectly at a certain pressure, go above that pressure and it will cool very poorly (think of a bell curve). As where r12 essentially cools better the more you add (think of a rising curve that tappers off), the compressor will probably be reluctant to take to much freon and cause damage but that doesn't mean you shouldn't keep an eye on it. Quote Link to comment Share on other sites More sharing options...
55trucker Posted April 29, 2011 Report Share Posted April 29, 2011 He also told me that it is harder to overcharge an r12 system mainly becuase r134a only works effectly at a certain pressure, go above that pressure and it will cool very poorly (think of a bell curve). As where r12 essentially cools better the more you add (think of a rising curve that tappers off), the compressor will probably be reluctant to take to much freon and cause damage but that doesn't mean you shouldn't keep an eye on it. What you were not informed is that this systems design (and similar later designs) allows for very little overhead. Therefore you cannot just load up on the refrigerant until the system cools to a point where you are satisfied. If you overcharge the system (because you don't know how much is presently in the system) you take the chance of damaging the compressor, this compressor is a variable rate compressor. There is no low cut out switch in the system that causes the system to repeatedly cycle when the low side drops to to a prearranged pressure (such as 25psi), there is only a low pressure switch that keeps the compressor from engaging when the system is empty. A properly running system once engaged runs 100% of the time. The compressor adjusts the flow rate of refrigerant depending on the load on the system in conjunction with the ambient temp coming thru the condenser and the condensers ability to cool the refrigerant after receiving the heated liquid from the evaporator. When charging a system the compressor is not the governing body that dictates when the system is full, the charge comes in on the low (suction) side of the system, while the system is running and you are charging, the low side is always lower than the pressure in the storage container (unless the source is empty). The system will continue to pull in the refrigerant as long as there is a source there. You are the governing body & have to be careful to not overfill & damage the system. Quote Link to comment Share on other sites More sharing options...
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