Amount of Oil in Air Conditioning System?

[edwardb]

I'm in the process of finalizing the Factory Five provided A/C setup in my new Gen 3 Coupe build. I have little/no experience with this and am using it as a learning experience. Something I enjoy doing plus I prefer not taking to an outside shop if not necessary. I'll document in more detail in my build thread when I'm further along. But right now I'm a little hung up on one aspect. Since I think this would apply across all models, I'll try here in the general discussion forum. Hopefully there are others with more A/C experience than me (wouldn't be hard...) that can give knowledgeable advice.

So the question. A/C systems have oil in the charge. The 05-14 Mustang 5.0 V8 compressor that FF provided in the A/C kit has a tag that says it's supposed to have 4 ounces of oil. Also gives the oil requirement. A Motorcraft specific PAG 46 oil, which I have on hand. I'm being very cautious and chose to drain the compressor and refill with the exact amount. So that's not an issue. But everything I've read and studied says the overall system requires additional oil. A current model Mustang GT 5.0, for example, lists 7 ounces of oil required. So should I add an additional 3 ounces when I do the fill? Seems like a lot for what I believe is a simpler system than what's in a Mustang. Many cautions about not having enough oil. But also about having too much as it can affect the cooling process.

The instructions from FF are a little vague. They show using a can of A/CPro 1st Charge which "has oil in it." That's it. No specific volume recommendation. I questioned this via email and was told the same thing again. So I bought a can of that product. It says right on the can "1st Charge is not a replacement for manufacturer's oil requirement." But it also lists 1 ounce of oil in the ingredients. I could interpret that as don't use the 1st Charge as the only oil in the system and the added one ounce is maybe enough along with what's in the compressor. Or could interpret as don't consider it at all and I need to add more. But how much?

This is one of the reasons I'm a little reluctant to take it to a shop that does A/C work. Without a specific manufacture's spec they may not be sure what to do. Much like many experience when trying to get wheel alignments.

Appreciate some feedback from those who know about these things. Thanks in advance.

[mike223]

Without a specific manufacture's spec they may not be sure what to do. Much like many experience when trying to get wheel alignments.



Agreed.

The magical thing about AC oil is it is formulated to be carried round and round through the system by the refrigerant (and stay scattered flowing through the system).

You won't get into trouble with "too much oil" until you get so much oil in it you slug the compressor - you can't compress a liquid, so something breaks - you're approaching that point if you're to the point of reducing efficiency due to not having enough refrigerant in it because you put too much oil in it - typically this would be indicated by an accumulator staying full of liquid oil, rather than refrigerant vapor.

You never really know how much oil is in there unless you start with all new components from scratch - rarely done except OEM.

Ford does plenty of testing - if they say 7 ounces for the current Mustang - evaluate the length of the hoses, Mustang vs. FFR - I think your educated guess of about 6 ounces is probably spot on. 7 or 8 ounces isn't going to hurt anything.



Hope that makes sense - especially the part about excess oil tending to collect in the accumulator.

[edwardb]

Thanks that's very helpful information. So a little more about the FF provided system. This is in my Gen 3 Coupe. I suspect a similar design in other systems they provide, although I don't know that for a fact. This system has only the following components: Compressor, condenser, receiver/dryer with trinary switch, and evaporator. Of course also the hoses and beadlock fittings hooking everything up and the high and low pressure connections. The evaporator they provide is a Siroco Boreal unit which has both heat and A/C coils. The unit has an expansion valve for the A/C, which if I understand correctly means this system does not use an orifice tube and accumulator which I understand is common in many automotive setups. Including probably the Mustang referenced. As I understand the receiver/dryer in this setup would act somewhat like an accumulator, but since it's on the high side not exactly the same.

Hopefully my neophyte status doesn't show too much on that description. Does this affect the amount of oil I should put in the system? I'm leaning towards the 4 ounces specified by the tag on the compressor and then adding two more before charging.

[mike223]

Hopefully my neophyte status doesn't show too much on that description. Does this affect the amount of oil I should put in the system? I'm leaning towards the 4 ounces specified by the tag on the compressor and then adding two more before charging.

The description you provide makes perfect sense.

In refrigeration, a receiver is designed to be in the (high pressure) liquid line and typically is made to make sure any liquid in the vessel goes out first - typically with a dip tube of some fashion pulling liquid from the bottom of the vessel.

An accumulator is the exact opposite - it is made to make sure all vapor is out of the vessel before any liquid could pass - it discharges off the top of the vessel - this is to prevent feeding liquid refrigerant (or oil in quantity) into the suction side of the compressor (xxx-death-xxx).


An expansion valve acts as the metering device - if it has a sensing bulb on it - it's a thermostatic expansion valve (TES) and the bulb needs to sense the temperature of the refrigerant (vapor) leaving the evaporator - thermostatic expansion valves typically aim to provide that the refrigerant leaving the evaporator is 10~15 degrees superheated vapor - to avoid feeding so much liquid refrigerant into the evaporator as to flood liquid refrigerant all the way back to the compressor and destroy it.


Orifice type metering devices are typically provided with accumulators because environmental variables affect an orifice (how much liquid it's feeding) much more than a valve (TES) that is monitoring superheat.

But an accumulator is certainly not an inappropriate addition to your system if you had a good place to fit one in.


Short answer - I agree you (especially) do not want to overcharge that system with excess oil (due to lack of accumulator)- so 4 + 2 sounds good to me.

[edwardb]

It's buried now so can't give much detail. But I recall the expansion valve on the back of the evaporator had a capillary tube and bulb. So that sounds like the TES you described. The system is all installed, hoses cut, fittings all used up, and little/no room anywhere. So I won't be making any changes. Appreciate the feedback. Very helpful and feel like I'm on the right track. I'll add up an update to my build thread when it's charged and running. First going to pull a vacuum and see how I did on the installation.

[TheDon]

Out of curiosity how did you crimp the hoses?
Let us know the results.

[edwardb]

Out of curiosity how did you crimp the hoses?
Let us know the results.

I bought the Mastercool 71550 Black Manual A/C Hose Crimper recommended by Factory Five in their instructions. Nice tool and worked very well.

https://thefactoryfiveforum.com/attachment.php?attachmentid=99215&d=1545151157

https://thefactoryfiveforum.com/attachment.php?attachmentid=99216&d=1545151165

[edwardb]

To close on this thread, successfully completed the system charge including the oil. Write-up plus pictures in my build thread: https://thefactoryfiveforum.com/showthread.php?26630-Edwardb%92s-Gen-3-Type-65-Coyote-Coupe-59-Build-Air-Conditioning-Charged-and-Working&p=402610&viewfull=1#post402610.