Automotive Air Conditioning Information Forum (Archives)

KATOOM on Mon August 03, 2015 12:35 AM

Year: 2001
Make: Dodge
Model: Ram
Engine Size: Cummins
Ambient Temp: 90-100*F
Country of Origin: United States

I have a 2001 Dodge Ram Cummins and the AC has always been fantastic. Turn it on and its instantly cold. Almost too cold.

Within the past year when I first turn on the AC I can hear a sizable "thump" coming from the passenger side fire wall area. Watching under the hood when this happens I can see the accumulator jar in a violent movement like someone has hit it with a hammer. But the AC had continued to work properly when this started to happen so..... That is until recently the AC started to take longer to get cold, and now it doesn't get as cold as it used to. Obviously something isnt right. I'm only guessing that the thumping accumulator has to be related to whats causing the AC not to cool as well. I did a search about my question first but nothing seems to be out there in this forum. I found in other sites that people described the same problem on other vehicles and there people talking about compressor slugging or bad accumulators. No one seemed to ever solve their problem.....or at least bother to say that did.

My knowledge about AC systems is limited to just knowing what the components are called and the very basic function. Other than that, I have no idea what to look for. Even if I have to take it to someone, I'd sure like to know what I'm up against before having them throw an erroneous bill at me claiming a huge issue which may not be true. Thank you for any help anyone can offer.

GM Tech on Mon August 03, 2015 7:57 AM

It is a design issue- liquid refrigerant gets trapped in A/D and then "explodes" upon rapid pressure drop inside when a/c compressor starts- seen it, heard it before- it is NOT related to your loss of cooling- you most likely have lost refrigerant elsewhere due to a leak---have your refrigerant recovered and weighed to confirm loss..

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

KATOOM on Mon August 03, 2015 1:33 PM

Interesting. Thank you.
But why would the thumping just start out of the blue? I've had this truck for going on 14 years and it started doing this just within the last year.

Also.....worth pointing out that I just asked an AC guy whom I trust fairly well and his opinion was that the thumping is a cause of all the freon oil draining back into the compressor as the truck sits. Because the compressor on these engines sit down low this is more exaggerated. Then starting the AC that first time causes a hydraulic of the system which throws all that oil back into the accumulator, thus the thump. But he as felt that when the compressor has to go through this its also very bad for the compressor and usually starts causing problems like metal being thrown pumped into the system. He felt that this may be why my AC isnt getting as cold. I guess I wont know until I can get some gauges on there to see what the pressures are.

GM Tech on Mon August 03, 2015 1:40 PM

It has to do with the size of the desiccant bag and the amount of refrigerant trapped in the oil in the desiccant- it was a big issue on GM B-cars - police cars back in the mid 90's- changing the size of desiccant (smaller) helped as I recall.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

KATOOM on Mon August 03, 2015 1:46 PM

Hmmm..... Well then let me ask this. If the AC system is under a constant state of pressure/vacuum then why would anything (oil/desiccant) ever flow back down into the compressor? Wouldnt a leak in the system have to occur for that to happen, or am I totally confused as to how the AC system works?

Again, I'm wondering why this thumping started recently and not over the entire time I've had the truck.....? And why the AC isnt getting as cold now.

GM Tech on Mon August 03, 2015 2:05 PM

Thumping is usually a once a day occurance- about 1 sec after a/c is turned on- and only repeats the first start up of the day. You may have added more oil - so more is retained in the accumulator- there is about 3 1/2 ounces of oil in the accumulator at any given time.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

KATOOM on Mon August 03, 2015 2:44 PM

So a system which has gotten low on freon wouldn't have a reason to do what we're talking about with the accumulator? No relation?

mk378 on Mon August 03, 2015 3:56 PM

Oil circulation is impaired when running undercharged. This could lead to pooling of oil in the evaporator and accumulator and thus more thumping. You really should confirm that the charge amount is correct by weight, and if it is not that then you would start looking for other problems.

Edited: Mon August 03, 2015 at 3:56 PM by mk378

KATOOM on Mon August 03, 2015 4:22 PM

Thats what I'll do then..... Thanks.