W123 receiver dryer cut open - PeachParts Mercedes-Benz Forum

funola · #1 08-10-2016, 08:39 AM

https://www.youtube.com/watch?v=cnrd4GiLhsI

Dryer from my 85 300D, last ran about 3 weeks ago. System has a very slow leak somewhere. I've read on this forum (from a particular forum member) that the receiver dryer dessicant is submerged in oil. Well, not this one. There was at most 1/8" of oil on the bottom. Anyone else have pics or video of one cut open?

compu_85 · #2 08-10-2016, 09:12 AM

Most of the oil will be stuck to the desiccant. If the whole dryer was full of oil it means the system has *way* too much oil in it.

I'm trying to recall... isn't the total system oil like 10oz?

-J

funola · #3 08-10-2016, 09:21 AM

I was able to pour the dessicant beads out of the filter canister and there was no visible oil binding the beads together. Total oil capacity is 170 CC, or 5.8 oz.

If the dessicant's purpose is to absorb moisture, wouldn't you think it should be oil phobic? If it is soaked with oil, wouldn't it have less capacity to hold moisture?

funola · #4 08-10-2016, 09:30 AM

funola · #5 08-10-2016, 09:34 AM

Signs of rust on the bottom of the can, made from iron. I remember cutting open a receiver dryer that was made of aluminum, can't remember which vehicle it came from... might have been from a 92 Jetta.

Demothen · #6 08-10-2016, 09:38 AM

Is one of those disks some sort of filter?

funola · #7 08-10-2016, 09:40 AM

Yes, there are 2 of them, one below and one above the dessicant (dessicant is not in a bag)

compu_85 · #8 08-10-2016, 09:45 AM

If you roll the beads around on your fingers I bet you'll find they're covered in oil. That's what I meant, they don't absorb oil but oil sticks to them (like any surface).

-J

funola · #9 08-10-2016, 09:57 AM

Yes, I am sure they will feel oily on the surface. My point was that the beads were not submerged in oil. With that said, when adding oil to a new system, I do not think most of the oil should be added to the dryer. I would add all of it to the compressor (because that is where it is needed for lubrication), and turn it by hand many times before running the compressor to alleviate hydro lock. When I took apart an R4 a few years ago, I remember there is a small sump of sorts. I still have that R4 laying around, I'll look at it again and see whether 6 oz of oil will hydro lock it or not.

compu_85 · #10 08-10-2016, 10:13 AM

I'd suggest adding half in both places. If you add oil only to the compressor most of it will get pumped out when you start the AC running, then have to go through the complete loop before it gets back. If you add the oil in multiple places it takes less time for oil to circulate back to the compressor.

leathermang · #11 08-10-2016, 10:46 AM

Quote:

Originally Posted by compu_85

I'd suggest adding half in both places. If you add oil only to the compressor most of it will get pumped out when you start the AC running, then have to go through the complete loop before it gets back. If you add the oil in multiple places it takes less time for oil to circulate back to the compressor.

Yes, the FSM suggests spreading it around when adding... sometimes suggesting measuring the amount which came out of a 'section' or part and replacing that with the clean oil portion....

leathermang · #12 08-10-2016, 10:49 AM

https://macsworldwide.wordpress.com/2010/07/13/three-important-functions-of-the-receiverdrier-in-your-cars-ac-system/

leathermang · #13 08-10-2016, 12:15 PM

Quote:

Originally Posted by funola

Yes, I am sure they will feel oily on the surface. My point was that the beads were not submerged in oil......

If you look on page 83.6/530/2 of the MB AC FSM you will see a picture of your receiver dryer. It shows the desiccant covered by the liquid refrigerant with the oil mixed in with it and the outfeed tube coming from the bottom of the unit... thus forcing the refrigerant which is carrying the oil to lube the system with it through the desiccant pearls and then out to the Txvalve.

THE CONTEXT in which the receiver dryer relationship of liquid to desiccant level is DESCRIBING to people why it is not possible to use vacuum to remove any moisture which has been acquired by the desiccant. This is of course just before saying that it is recommended that any time the system is opened up... or has a leak ... that the receiver dryer should be replaced to reduce the chances that moisture mixed with refrigerant and oil will form corrosive acids inside the system which can cause metal flakes to come off metal parts of the system and potentially clog small openings like the Txvalve..

vstech · #14 08-10-2016, 02:28 PM

I'm not sure who told you the dessicant was submerged in oil... maybe submerged in liquid refrigerant that had dissolved oil in it... there really shouldn't be any liquid oil stored anywhere but in the compressor... all remaining oil in the system should be in suspension in the refrigerant.

the beads chemically attach themselves to moisture, drawing it out of the refrigerant and oil.

leathermang · #15 08-10-2016, 03:43 PM

Quote:

Originally Posted by vstech

I'm not sure who told you the dessicant was submerged in oil... maybe submerged in liquid refrigerant that had dissolved oil in it... there really shouldn't be any liquid oil stored anywhere but in the compressor... all remaining oil in the system should be in suspension in the refrigerant.

the beads chemically attach themselves to moisture, drawing it out of the refrigerant and oil.

Well, that does not exactly match the implications of the instructions for the R4 from the MB AC FSM...

83.6-520/4 F4 says
''''...... if one component of the system must be replaced , fill a certain quantity of oil directly into the new component '''''

earlier they had talked about , when taking stuff apart, measuring the amount of oil in each removed component.. so I assume they mean to replace that amount with new oil into the new component.