Good points, all, Fox.

does putting a vacuum on the system get all the oil out? or does it leave some in? if so, where is it? in the compressor? the drier?

if I go the long route, I want to make sure I'm putting in the right amount of oil.

also, your note about compressor noise -- that's one of the things I noticed when I did this last using the combo cans of oil & refrigerant -- compressor noise. rattley.

I have a Weber carb, so no dashpot or idle up mechanism except for my foot, which, at stops, I hold it at 1000rpm.

just got a call from the shop. my Mazda's ready. I'll come back and post the results for comparison -- I know it's not an apples to apples, but it's an R-12 to 134 conversion, so if anyone's interested in a "professional" result...

The oil is in the compressor. The vacuum removed moisture from the system, I think the moisture reduces the effectiveness and can lead to problems. The right amount of oil to add back in should be listed in the Factory Service Manual. I'm getting ready to convert my truck so I've been reading up. Supposedly the 2 oils (R12 and R134) are not compatible...I'm not sure why but I'm going to flush my compressor, change o-rings, and of course new drier. My condenser is busted, so new one of those for me as well.

I can get the temp down to 46-49 F . I think the problem with the oil is that 134a doesnt mix well with the r12 oil so it doesnt circulate through the system well,which would make for a noisy compressor.The only systems Ive done this on were old so I dont know if they were any noisier than normal.In a perfect world tear it down,get the old oil out and replace it for best results , my old Dodge truck gets the $35 kit from wal mart,my Toyota doesnt have ac

what are you going to use for flushing? ackits recommends against flushing the compressor with any type of solvent. for all the other components except for the drier, we used acetone and compressed air into a bucket.

I've heard the same on moisture in the system.

Ester oil is compatible with R-12 residues if I've read correctly on the can. apparently, pretty much any of the 134 products out there now are compatible with R-12 residues and oils.

those are good temps! my compressor is rattley. I am curious about the separate oil & refrigerant method. I still don't understand for sure whether the oil you add stays in when you evac.

The oil is throughout the entire system. A lot of it lives in the compressor, but there's plenty in the condenser, the evaporator, and even the lines, especially where they droop down. The compressor is not like a 4 cycle car engine where there's a sealed and seperate crankcase. It's more like a 2-stroke engine, where everything goes through the crankcase.

You will not get the oil out by vacuum. All that does is pull out everything that boils at low pressures. To get the oil out, you've got to manually remove components and drain them. Tedious, to say the least. But if all you do is the compressor and condenser, you've got most of the oil.


I got my oil from the A/C-kits.com listed above in the thread. BVA auto-100 (I went and looked). The quantity of oil in the system isn't hyper sensitive or overly precise. You can find lots of info out there on how much oil you put in, accounting for the various components. I don't remember the quantities, but since the bottles are 8 oz, and I did two vehicles with one bottle, I'd say I used roughly 4 oz per vehicle.



It surprised me how much difference the oil change made. I wouldn't have done it except the replacement oil was quite cheap.


In the junkyards you will find many electrical solenoids and such that can be fitted up quite easily to your Weber. I'd consider it a worthwhile upgrade, but you can do the job with your foot.

okay, so on the drive home tonight, about 7pm, outside temp around 72*, 57% humidity, I was getting 49-52* output at the vents on the '87 Mazda 626 that I had retrofitted at the shop.


okay, this makes perfect sense now. I just wanted to make sure that evacc'ing the system doesn't pull out the oil I'd be pouring in.

speaking of boiling at lower pressures -- water at -30" -- is it hot, or does it boil cold?


okay, I think this is the same as the Ester oil. and for the comments above, the can of Ester oil says that it's compatible with the chlorine residue of R-12 refrigerant oil, and that it's compatible with other auto refrigerant oils.


yeah, I'm really curious about this now. it's been bothering me since I retro'd it. I'd like to think I'd have burned it up by now were it not getting the lubrication it needs, though, but I feel better with the oil & refridge separate, I think. don't know why; I'm just a stickler for detail and doing things properly.


I wouldn't mind finding something like this, but I wouldn't even know where to begin looking or how to go about rigging it up. any addition info would be greatly appreciated.

thanks for all the information here guys. this has answered a lot of my questions.

The temperature things boil at is a function of the pressure they are under. Water at sea level boils at 212 degrees because that's how hot it has to be to overcome the pressure on it. Lower the pressure and you lower the boiling temperature.

For fun, I can show you how to boil water with an ice-cube as a science experiment. Take a glass soda bottle with a good cap, fill it about 1/4 full of water, and put it in a pot of water on the stove. Now bring it to a boil so the water inside the soda bottle is boiling. Let it boil for a minute, so the bottle is well filled with steam. Turn the heat off and immediately cap the bottle. Take it out and let it cool down. This creates a vacuum inside the bottle. Now rub the top half of the bottle with an ice-cube. This really creates a vacuum inside the bottle, and the water in it starts boiling because of the vacuum.



I've done several conversions in the past without dumping and switching the oils, and a friend has done roughly a hundred of them over the years without incident. It really was on a lark that since I had the opportunity to do an oil swap that I did it. I probably wouldn't bother on a car that I was merely changing the refrigerant on. But if I was removing components, I would.



Your Weber is the two barrel downdraft unit right? That was oem on many cars back in the 70's and 80's. If you go to a junkyard that has older cars of this era in it and you pop open the hoods, you will see carburetors that look just like yours there looking at you.

If you look at the linkages on them you will see some have a dashpot connected to nothing. That is to keep the engine from stalling when you let go of the throttle. That's not the piece you're looking for.

But you will also see either an electric solenoid connected to the throttle linkage, or a little vacuum can connected to the intake manifold with electrical wires, these are idle control units. Find one with a linkage that looks like yours, or something like yours, and you can combine parts to make it work on your truck.

that's great!!! duh, I've had a few chemistry classes and completely forgot about PV/T.


okay, I leaning towards being overcharged now, if not simply a limitation of the system and undersized condenser.


thanks, that's excellent information!
unfortunately, most of the junkyards I've been to recently don't keep old inventory. hard pressed to find anything before 1990.

Just bought one of those $35 conversion kits for my brother's 88 Runner tonite. The kit comes with 2 hi side adapters and 1 lo side adapter. Neither of the hi side adapters will thread onto his compressor and the lo side adapter is way too long to be able to get the charge hose onto it once it is threaded on. The space down there is just too tight, just no room for the connector. Anyone experience this? The lo side port on the compressor seems like it is in a bad place.

On one of my vehicles I installed a new ND compressor and I use a infrared temp gun on the vents and I read from 34 degrees to 40.