A/C System Recharge. How much oil to add?

[nc91]

Hi, I recently bought a 2004 (late model 2003) Expedition 4.6l. Wouldn't start and it turned out to be the R303 relay issue. ($22 later, runs like a champ!)
The previous owner told me that the ac didn't work. I hooked up my gauge set to it and found that there was no pressure/no refrigerant in it. Almost as if it either leaked down completely or was evacuated previously and never replaced. The previous owner told me that he had it looked at several years ago and couldn't remember what they did but he didn't have it fixed. I pulled a vacuum on it and it had no issues and held a vacuum with no trouble. I went ahead and got enough R134a to refill it (54oz for front and rear air) and began to fill it. As expected, the compressor kicked in as soon as the pressure got high enough and cycled normally until I reached about 48oz. I finished filling it to right at 54oz using a scale with the last can. Sadly, I didn't think about re-adding oil... Now looking back, I don't know if oil came out with the previous owner, and the R134a that I used was straight refrigerant without oil. In doing some reading online, some folks said as long as no major components were replaced, you shouldn't need to add oil. Others said add 1 oz if recharging a system from vacuum. Would it be wise to get an oil charge can with the proper PAG oil and add that or have I passed that point? The system is running great and I'm getting normal pressures on the high and low side and the compressor isn't making any noise at all. (other than normal) It appears that it's the original parts on the truck so I'm sure it's seen better days but I'd like to keep it working as long as possible before I have to swap parts. I really appreciate any insight you can give.

 

[nc91]

Just to clarify, it cycled alot up until about 48oz of refrigerant then began to only cycle as normal after that. Sorry if I was confusing.

 

[Flexpedition]

This Ford page suggests in your dual zone unit, there should be (gasp!) 14 oz of oil.

http://assets.clickmotive.com/Customers/3/31378/file/REFFIGERANTOILCAPACITY.pdf

I'd speculate these was likely some residual oil in the system that was original to the truck, but its just a guess. Me - I'd evacuate all of it, pump it down and let it hold a vacuum for a few hours or overnight. If it holds strong, then add the proper amount of oil, then new Freon. Certainly before the summer months arrive.

 

[nc91]

Thanks so much for the reply! I guess I'm confused about how the oil travels. Much of what I read said that some of the oil is mixed with the refrigerant but the components retain the vast majority of it. Are you saying that all the oil is likely out of the system and I shouldn't run it at all? Or are you meaning that it is some amount low since no components were replaced? I guess I'm meaning, is there likely enough oil in it to run it for a while or should I stop all use until I can afford to have it fully serviced? I don't have any way to reclaim it so I would have to go to a shop and pay to have that done. Thanks again for all your help!!

 

[shadow460]

The best way to check for leaks is a hydrostatic test with dry nitrogen. It takes a few minutes and leaks can be pinpointed with soap and water.
That said, I believe you've got a satisfactory leak test.
My own Expedition also calls for 14 ounces of PAG 46. I always pull a vacuum and suck the oil in--it works wonders on split systems. After I spilled the oil from my compressor, I put the rest of one bottle a d an entire second bottle of pag oil in the system. It's been running a couple months now.
Yes most of the oil stays in the components. If you're worried abour lack of oil, buy one of those oil charge cans and put in there.
I have never measured oil precisely in an AC system like I should, but I have still had good results with my work.
I do residential HVAC work as part of my job, if that helps.

 

[shadow460]

Oh, if you are putting in that much 134a, buy a 30 pound jug of it and forget paying $25 a pound for it at O' Reilly. That's highway robbery.
You can also fill it with certain gas dusters. You'd have to change the pressure switch for one out if an R12 system. I did that on an antique F-150 and its ac worked like a champ.

 

[nc91]

Thanks!!