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Old 08-12-2015, 09:15 AM
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Default Anyone experience compressor slugging?

Just checking around and seeing if anyone has ever experienced AC compressor slugging on their trucks.
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Old 08-12-2015, 09:34 AM
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No, I haven't, but they usually don't take kindly to that......... You having problems?
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Old 08-12-2015, 10:34 AM
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Well yes and no. Over going on the past year, when I first turn the AC on, that initial cycle of the compressor will cause a very noticeable "thump" against the passenger firewall area. You can feel it too..... I never bothered to look either but a couple weeks ago I checked under the hood and sure enough the accumulator jolted. Although I'm not sure if this is the accumulator moving or the evaporator moving the compressor. Either way it only happens upon that first start of the AC. Then all is good.

I tried to research the issue and found that there's something called compressor slugging which especially plagues compressors mounted low on an engine because the oil/freon can drain back into the compressor as it sits and then its forced to shove all that goo out when it first cycles.

But saying all that, given the very few responses I got and the limited info I've found on the internet, I'm wondering if this is the problem.

And.....to go on some more. Coincidentally the AC was not getting as cold a couple weeks ago so I had a friend who does AC check the pressures. He said that the pressure was very low and the compressor was sucking it down when it cycles. So he added on little can whereby the low side came up to 40 and the high side was around 280, idling at around 85* ambient. AC regained its coldness and the only time I drove the truck since then, it didnt thump. Coincidence.....I dont know. But, I did read from one source that a system low on freon will not run efficiently and not pull the oil through the entire system properly and allow the oil to accumulate in places. Potentially affecting the compressor.

I'm no AC guy but there seems to be a whole lot of information and things to know when dealing with these systems.
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Old 08-12-2015, 10:44 AM
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When an AC system is running there is oil throughout the system. With the proper amount of refrigerant the oil will move with the flow, but if it is low I can see where the flow is not sufficient to move the oil. I have a hard time figuring out why the oil would accumulate and slug the compressor only when low and sitting. Far as the accumulator jumping, that confuzzles me too. All it is is just a tank so that if any liquid refrigerant leaves the evaporator it will boil off and allow nothing but vapor to return to the compressor.
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Old 08-12-2015, 10:58 AM
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As it was explained, the freon will run to the lowest location in the system which is why low mounted compressors are more prone to slugging. This is such and issue on imports that its been known that compressors can literally blow apart from the hydraulic pressures trying to shove all the accumulated freon back up through the system. However, slugging can be experienced in many fashions too. I'm just confused as to why not more people haven't experienced this with their trucks.
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Old 08-12-2015, 11:06 AM
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Yea, I know that compressors are designed to pump vapor and not liquid, but under "normal" circumstances there is not enough pressure in an idle system to allow the vapor to condense to liquid (or at least not much). Yes, in theory the liquid will run down hill to the compressor, but the accumulator should be capable of preventing liquid from reaching the compressor especially since the suction line is higher than most of the system just before the compressor. Now, back to your original question, I haven't heard of these compressors slugging very often.
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Old 08-12-2015, 11:12 AM
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Thinking about this more, I wonder if you have a slug of oil that is pooling in the accumulator so that when the vapor does 'break through' the slug there is an increase in pressure from the slug to the compressor causing things to jump? If you look at the construction of an accumulator you can see where that may be what is happening.


More info here: http://lincolntrial.integr8cms.net/i...tioning-system
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Duct Tape can't fix stupid, BUT it can muffle the sound
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Old 08-12-2015, 02:15 PM
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I'll read through that, thanks.
And I guess I should point out that from what I have read on the topic, Ford has a TSB regarding the slugging issue and I though I remember this involving replacing the accumulator with a different design.
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'01 2500 Sport 4x4 5spd, EZ, RV275's, 4" without muffler, no silencer ring, aFe intake, 2 lo kit, Isspro Boost, fuel pressure, and EGT all on pillar, Westach Transmission/Differential temp gauge in dash pod, Fast Coolers/exhaust blanket, Raptor 100 with big line kit, Pac Brake, Rancho 9000's, Custom Diesel steering box brace, 285's
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Old 08-12-2015, 03:02 PM
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Tom that website is AWESOME..... Thank you. Great video and great animation showing the actual function of the system under different conditions.
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'01 2500 Sport 4x4 5spd, EZ, RV275's, 4" without muffler, no silencer ring, aFe intake, 2 lo kit, Isspro Boost, fuel pressure, and EGT all on pillar, Westach Transmission/Differential temp gauge in dash pod, Fast Coolers/exhaust blanket, Raptor 100 with big line kit, Pac Brake, Rancho 9000's, Custom Diesel steering box brace, 285's
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Old 08-12-2015, 03:06 PM
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You are welcome, sir! Glad I could 'de-mystify' how the AC works!
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Duct Tape can't fix stupid, BUT it can muffle the sound
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