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#1
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Need some experienced A/C diagnosis
So I am having a problem with my 300TE's A/C...
I think there is a blockage in the system somewhere, but I need help diagnosing this first. I evacuate the system, and vacuum down to ~29 hg. The problem is that with only 12oz of refrigerant, I am getting 45/320 psi lo/hi. (25/380 at 1500rpm). That is only a 1/3rd of the recommended capacity for r134a (the recommended is ~28oz). Why would my pressures be so high after only ONE can? The only thing I can think of is that there is a blockage? Could there be anything else that could be causing this? I'm purging the lines of air before I begin and vacuum held fine for 30mins after I shut off the valves. I need some help diagnosing here its driving me crazy!!! Is there a specific test I can perform so I don't have to waste hours and hours swapping parts unnecessarily?
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2016 Monsoon Gray Audi Allroad - 21k 2008 Black Mercedes E350 4Matic Sport - 131k 2014 Jeep Wranger Unlimited Sahara - 62k 2003 Gray Mercedes ML350 - 122k Last edited by ps2cho; 06-12-2016 at 02:49 PM. |
#2
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Using R134a you need to calculate by the ambient air temp.
At 90F, using R134a, you should be seeing 45-55 psi on the low side and 250-270 psi on the high side. It appears you could have a orifice tube/expansion valve problem. Evacuate, replace, flush, vacuum and re-fill. Ain't automotive A/C fun!
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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now |
#3
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Feel the high side tubing with the system running. It should be quite hot to the touch all the way to the txv. If you find a spot where it turns cold or cool, there is your blockage.
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#4
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Possible the drier desiccant bag contents have plugged up the orifice in the drier.
Remove drier and blow through with air line. Clear ? Then blow through rest of system isolating the hi side and lo side as two separate systems. Possible TXV has jammed closed, nearly closed or blocked.. Ran mine with Duracool up to 200,000 miles. Duracool may not be legal where you are. FYI : Holding a vacuum is no indication it will hold pressure. . .
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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ] "A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money." |
#5
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If there was a restriction, you should be able to find it easily. Normally it will produce an ice ball, and you will have super high high side, and or super low low side.
My experience with mb Ac systems is that you should just charge it by weight and don't look at the gauges. My vague recollection of my 300e was that the pressures were high after about half the r12 was in. I just stuck to the scale and I had perfect Ac after.
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Eugene 10 E63 AMG 93 300te 4matic 07 BMW X3 14 Ford F-150 Fx2 |
#6
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Quote:
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![]() 1990 190E 3.0L |
#7
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Ignoring the pressures is asking for trouble. If I just willy nilly charged by weight then I'll have the compressor blow a seal as pressures would easily get above 450psi...you MUST use gauges, every time!
Thanks for the line info. I ordered a Infrared Temp Gun and I'll get a readout across all the lines and see what it shows and reply back at that time.
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2016 Monsoon Gray Audi Allroad - 21k 2008 Black Mercedes E350 4Matic Sport - 131k 2014 Jeep Wranger Unlimited Sahara - 62k 2003 Gray Mercedes ML350 - 122k |
#8
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Quote:
Charging by weight is the only truly accurate way of recharging a system. The car should never get pressures that high, there is a cutout switch on the high pressure line for those situations. Also, the fans should be running full speed after 350 psi. You keep thinking that because you had 350 psi with 12 oz of r12 in , that you will have 3x the pressure with 3x the refrigerant in. This is not true. The system is already pumping at capacity the moment there is enough refrigerant in there to liquify. Remember, the refrigerant is the stuff that absorbs the heat from the cabin. With only 12 oz in, there is not enough for you to notice a difference. The system is is working at full pressure, just not enough volume to make a difference. Just charge the system 2.2 lbs, or 1 kilo, and be done with it.
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Eugene 10 E63 AMG 93 300te 4matic 07 BMW X3 14 Ford F-150 Fx2 |
#9
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Probed with the temp sensor today, no cold areas or anything that seemed odd. All the high side hoses were too hot to touch, and the low side was mediocre cold at best...
Condenser inlet and outlet temps show a 80F drop, so the fans are shedding heat fine and its not a blockage in the condenser...the pressure is just off the charts. Here's proof the pressures keep going up and up. I added about another 1/2 a can in. I stopped because with whatever is going on, is not following your theory. This is at 1500rpm with both aux fans going full speed. Ambient temp right now is 98F. Vent temps were showing 63F. ![]()
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2016 Monsoon Gray Audi Allroad - 21k 2008 Black Mercedes E350 4Matic Sport - 131k 2014 Jeep Wranger Unlimited Sahara - 62k 2003 Gray Mercedes ML350 - 122k |
#10
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The logical explanation is that the condenser is not properly shedding heat. Make sure that the aux fans are turning the correct rotation. For about the last decade the replacement fans come with the wiring backwards in the plug. I've seen plenty of fans spinning the wrong way.
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![]() 90 300TE 4-M Turbo 103, T3/T04E 50 trim T04B cover .60 AR Stage 3 turbine .63 AR A2W I/C, 40 LB/HR MS2E, 60-2 Direct Coil Control 3" Exh, AEM W/B O2 Underdrive Alt. and P/S Pulleys, Vented Rear Discs, .034 Booster. 3.07 diffs 1st Gear Start 90 300CE 104.980 Milled & ported head, 10.3:1 compression 197° intake cam w/20° advancer Tuned CIS ECU 4° ignition advance PCS TCM2000, built 722.6 600W networked suction fan Sportline sway bars V8 rear subframe, Quaife ATB 3.06 diff |
#11
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What was the pressure at idle?
At 40/ 440, looks like there is a restriction somewhere. The expansion valve is a common place to clog.
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Eugene 10 E63 AMG 93 300te 4matic 07 BMW X3 14 Ford F-150 Fx2 |
#12
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I know you said you vacuumed down to -29, but those numbers could be also indicative of air in the system. When you vacuumed down the system did you do it for at least 15 - 30 mins on low and hi side? Also, before you started charging, did you crack the yellow feed hose first to purge the air out and let the r134 fill up the hose before you introduced the refrigerant into the system? I would say vac the system down again and follow the recommended charging protocol. Or, try getting the rpms up to about 2500 and see where you are at with ac vent temp and the high and low side pressure. If it stabilizes at the higher rpm and then goes back up, you could have a problem with the compressor not properly compressing the refrigerant.
Also, check out this attachment. Good luck.
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![]() 1990 190E 3.0L Last edited by lsmalley; 06-14-2016 at 03:09 AM. |
#13
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at 450 psig with runnign system your liquid line should be extremely hot, try dousing the condenser with running water and see if it helps.
In one instance in a another brand car I was repairing this behaviour was caused by a faulty expansion valve - its high side was reaching 400 psi while the low side was at 30 and going towards 20 when revved. It maybe that you have a lot of oil in the system.
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2012 BMW X5 (Beef + Granite suspension model) 1995 E300D - The original humming machine (consumed by Flood 2017) 2000 E320 - The evolution (consumed by flood 2017) |
#14
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I agree Charging a system by other means than a recommended required Weight is only charging to the systems limitations. Inefficient condenser , TX valve not fully opening. sensor out of speck. Vacuum??? if you don't use a vacu stat YOU ARE ONLY GUESSING Yes the gauge says you have a good vacuum , But in reality without a vac u stat you would be surprised at how much you could be off a SAFE vacuum. Remember what the vacuum is doing . Not sucking crap out the system . Only lowering atmospheric pressure to allow moisture to BOIL off and out the system. If you want to blow the lines NITROGEN not your air compressor. AIR is Moisture it just doesn't mix. Pressure test a home A/C with air . You will have a hole in the ground where it once used to be. |
#15
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Quote:
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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ] "A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money." |
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