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Thread: Top off Truck
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08-21-2011, 03:34 PM #1
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Top off Truck
Need to top off my truck w/ 134a. I'm not sure how to do this. My first thought is to monitor superheat due to a fixed orifice MD. Is this right? I don't want to recover/evacuate due to a leaking evap core (which i will replace next year), I don't want to pull any moisture or non-condensables into the system.
Still learning....
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08-21-2011, 03:59 PM #2
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Yeah, superheat & check for some subcooling while you are at it. Most important is put a brick on the gas pedal and try to hold steady at about 1800 rpm. Open all of the vents, put the fan on high, and set the a/c to "max" or "recirculate." Don't worry too much as there is usually an accumulator in the system, but obviously don't go over the nameplate charge.
Your split will be high as automotive systems have huge capacity - usually 3 to 5 ton - with a very little fan...
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08-21-2011, 04:16 PM #3
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I always jump out the pressure switch to keep the compressor running and shoot for a 13º superheat reading on a fixed orfice, if it has at TXV I shoot for a beer can cold suction line.
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08-21-2011, 04:59 PM #4
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None of these methods are proper. Evacuate the system and weigh in the charge
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08-21-2011, 05:12 PM #5
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Kind of hard to do with a leak that you are not ready to fix. 15 minutes to get you by with some cold a/c, or 1/2 to a full day ripping out a dash to replace an evaporator...
Originally Posted by Joe Harper
Or he could take it to an ASE and 609 certified professional (proper thing to do). Then that guy can dump a pound in and call it good...
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08-21-2011, 05:20 PM #6
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/agree Originally Posted by cjpwalker
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08-21-2011, 05:46 PM #7
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If you're sure the leak is in the evap. Try a small can with sealant in it from the auto parts store. Maybe you won't have to pull the dash.
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08-21-2011, 07:21 PM #8
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dump in one of those small cans. if the accumulator and suction like are cold while it is running, stop. If it ain't cold, add another can.
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08-22-2011, 12:45 PM #9
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ive seen r134 cans at the auto parts store with the hose and a gauge. the instructions were to turn on a/c on high and fill till the needle is in the middle of the green area. now that's scientific.
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