Charging a new A/C system

[da_raabi]

I'm in the process of finishing up the rebuild of my A/C system. This will be a 100% new system. Evap, comp, cond, lines, hoses, etc. all replaced.

I plan to attempt charging the system myself. I can rent the gauges and vacuum pump at AutoZone, and know the basics of how to use them.

My question is: what is the capacity of the system when completely new, how much oil do I need, dye, etc?

I've never worked on A/C before, so any tips and tricks would be big time helpful.

The truck is a 1986 C30 454 with the A6 type compressor.

 

[75Monza]

Hey da_raabi, did you keep it R12 or swap to 134a set-up? The weighted volumes between the two are different from what I remember. I did the conversion on my 86 burb with dual ac, wasn't quite as cold as the r12 was, but still way better than 4/60 ac, lol. Seen somewhere that the rule of thumb for oil charge in your truck is 6 oz in the compressor, 2 oz in the accumulator, 1 oz in the condenser, and 1 oz in each evaporator on a brand new, or otherwise empty, system. That's a total of 10 oz of oil for a 2-door cab. The net charge should be 3.2 lbs (~51 oz) of R134a (or about 4.25 12-oz cans), plus 10 oz of refrigerant oil (6 oz poured directly into the compressor suction port, the balance poured directly into the accumulator). Haven't done a system for 14 years, so might need to double check that, sure someone else could chime in since my memory is one step away from dementia anymore.

 

[Preston]

Hey I just found I need a new ac compressor for my 85 Silverado where is the most economical place to get them?

 

[75Monza]

Rock auto or ebay, just be careful since the price/life ratio can nail you.

 

[QBuff02]

I'm in the process of finishing up the rebuild of my A/C system. This will be a 100% new system. Evap, comp, cond, lines, hoses, etc. all replaced.

I plan to attempt charging the system myself. I can rent the gauges and vacuum pump at AutoZone, and know the basics of how to use them.

My question is: what is the capacity of the system when completely new, how much oil do I need, dye, etc?

I've never worked on A/C before, so any tips and tricks would be big time helpful.

The truck is a 1986 C30 454 with the A6 type compressor.

Most compressors come with oil already in them. I said MOST. However, to properly charge an a/c system you have to pull a vacuum on it, I usually do it for about a half hour. it draws contaminants, moisture, debris, and unfortunately OIL out of the system. just how much can be a bit of a guessing game, that's why those fancy machines (i've been using ours more as of late) have a part in the system just for the drawn (removed) oil to be extracted and collected and another part to re-inject the system with new oil. Vacuum pumps don't have that luxury of just how much exactly so it can be a bit of a guessing game. After I draw a vacuum I usually let it sit for about a half hour to see if any of the vacuum in the system comes off, that way you know if you have a leak or not before you go any further and you can correct it before charging. Generally with a system, say, if you are replacing a line or the receiver/dryer you will lose about 3/4oz of oil in the vacuum process, so if I take out that much I generally put in about 5ish ounces of NEW oil after the vacuum. And with a vacuum on, it will suck the oil right in. I've always felt I'd rather have a touch more oil than not enough. But you'll have to look up the specs to determine just how much it calls for. Also, make sure you lubricate all the new o rings with compressor oil while installing. Again, I'm not sure on the charge for your system but find the specs or someone here will know. Some people like to charge the low side, some like to charge the high side. I always charge the low side. Some people like to come off the top of the can and some people like to charge with the can upside down. Gas/Liquid. This also depends on what type you are using to fill with. We use the big cylinders at work obviously. and also, Most of the new oil has dye already mixed in, but it depends on what you buy. if the oil has a lime green tint, it's dyed. The beauty of running a good vacuum is it will always suck refrigerant in to the point the compressor will kick on. As you know, when a system is low, the compressor clutch won't engage. Just take your time and double check everything before you start and as you go. And rule #1- If it don't hold a vacuum, it won't hold a charge. Let me know if I can help further, but your system specific info someone here will know more than me unless I research it.

 

[Preston]

Quincy, I just installed a new compressor in my 85 Silverado, question I need to go my friends auto shop about 5 minutes away. But I guess if there is no charge the compressor will not cut in until it is. This will be the first square body of mine to have the ac work thanks for the information

 

[QBuff02]

Quincy, I just installed a new compressor in my 85 Silverado, question I need to go my friends auto shop about 5 minutes away. But I guess if there is no charge the compressor will not cut in until it is. This will be the first square body of mine to have the ac work thanks for the information

This is correct. A/C systems have high/low pressure switches. if it's got too low or too high of pressure (due to charge problems or say a plugged orifice/restriction) the switch opens and it disables the compressor clutch basically for system protection.

 

[da_raabi]

So to get back on track with the thread... I am running R134. I really need to know the correct capacity and how much oil to use. Like I say, I've never charged an A/C system myself before so any kind of walkthrough help would be awesome.

 

[QBuff02]

So to get back on track with the thread... I am running R134. I really need to know the correct capacity and how much oil to use. Like I say, I've never charged an A/C system myself before so any kind of walkthrough help would be awesome.

I did some checking and the A6 style compressor requires per specs 10 oz of oil. Now since this is a new system, you're going to need more than that total. Add roughly 3 oz for the evaporator and another 1 oz for the condenser. The compressor should have oil in it, how much is always anyone's guess. and since most compressors come with oil in them, if it's sitting in the box, do not grab the clutch assembly and spin the pulley before installing and hooking up or it will puke it out of the ports. I'm assuming you've already assembled the system? If so, it would be best to crack a line and add some oil in the locations stated above, unless you are able to inject it into the system. The system if I researched correctly originally called for 3lb 8 oz of R12, but the conversion is generally considered 75% of R12 for R134, so you should be fine with roughly 3 lbs of R134. I tad less actually, But an even 3 isn't going to harm anything. Are you using the mini cans to fill this from? Be careful with what you buy as if you've added oil to the system or are planning to, a lot of those cans have oil included in them and you run the risk of over-oiling the system. But if you know that than you can plan for that and add or subtract accordingly. So 14 oz of oil and 3 lbs of R134 are your target numbers. Read through my posts here and whether they make sense or don't, feel free to shoot me some questions based off of them and i'll see where else I can help you from there.

 

[CorvairGeek]

Forgive me if I overlooked it, but the A6 has a sump and should have the entire oil charge in the sump. You can inject it in through the drain plug. The GM V5 compressor is the same way.

 

[QBuff02]

Correct for the oil amount on the compressor itself. But where I originally misunderstood it myself on this particular setup/system is if you are replacing components you also need to add back to the new components to compensate for the oil lost in doing so. Since he said this is a completely new system, the dealer manual states to add an additional 1 oz to the accumulator and an additional 3 oz to the evaporator. Assuming that the compressor holds a full 10 oz inside of it when installing, he'll be roughly 4 oz short per the manual for complete component replacement once the system is operational. As the tubes and insides of the system, especially the accumulator "absorb" the oil, it is lost for make up to the compressor. Also, if the compressor is a true R12 compressor, that he is converting to R134 either with new lines with correct fittings or the schrader adapter valves the oil will need to be drained out of it and refilled with the correct R134/PAG oil as R134 is not compatible with the Ester/mineral oil of the R12 systems.

On a side note, I'd say I probably do 80-90% A/C systems on heavy/construction equipment vs automotive. So in my experience I would tend to follow the manual more than my gut on this side of it until I was actually putting a charge into it and then I'm going to complete it by feel/what the gauges tell me.

@CorvairGeek any thoughts/input on the above?

 

[CorvairGeek]

As I have always understood the GM shop manuals, the quotes for amounts on replacements are only for repairs, not in addition to the new / clean system capacity. The system capacity would be the 10 oz in the OP's example.
GM has been very consistent with the recommendations for component replacement in the manuals since the 60s. Interestingly, in vehicles that used both good compressors (w /sumps) and those without sumps, the replacement amounts are smaller for the sump systems, as the oil is better retained in the compressor, rather than circulating like a 2 stroke mix. The A6 even has what is called an 'oil pump' for internal lubrication of the compressor in the old manuals that had real information. The full amount in the sump is important. Definitely a different design era.
An A6 with the new, double lip seal, AC Delco part number 15-30948, GM part number 2724954, makes an excellent setup. No oil line on the hood and leakage like the old, ceramic seal.
With a good clutch fan, you can easily run a 90%+ charge (90% is what GM actually recommends for conversions) with an A6 system. It will be quiet too, unlike an R4 which is always on borrowed time. The lower percentage conversions are killers on the sump-less systems, as you may not get sufficient oil return to the compressor.

 

[75gmck25]

In the past, many A/C shops had a conversion book that showed the recommended R134a charge for a conversion from R12, but those books are probably long gone in newer shops. Older conversions also still used mineral oil (IIRC) with R134a, but now recommend cleaning out the system and switching to PAG. I also switched to a Ford Blue orifice instead of the GM white orifice, because its supposed to work better with R134a.

The Pro6Ten compressor is supposed to be a new compressor in the same form factor as an A6, so it can be used as a direct replacement, but I've never actually seen one. Older rebuilt iron A6's were so unreliable that they coined the term "black death" to describe how they deteriorated and failed internally. It sounds like maybe the parts numbers above are a newer A6 model that is more reliable. After my first rebuilt A6 failed I paid for a shop to make new barrier hoses, and switched to a Sanden and brackets from Vintage Air. Its a lot smaller form factor.

As you make the conversion, if you have a 2 groove water pump pulley, take a look at Rock Auto and see what options you have for PS belts. My truck has the HD cooling option, and you can use a longer PS belt that goes over the crankshaft, water pump and PS pump. This means you have 2 pulleys driving the water pump, and if you lose one of them you will still have an operating cooling system.

Bruce

 

[CorvairGeek]

In the past, many A/C shops had a conversion book that showed the recommended R134a charge for a conversion from R12, but those books are probably long gone in newer shops. Older conversions also still used mineral oil (IIRC) with R134a, but now recommend cleaning out the system and switching to PAG. I also switched to a Ford Blue orifice instead of the GM white orifice, because its supposed to work better with R134a.

The Pro6Ten compressor is supposed to be a new compressor in the same form factor as an A6, so it can be used as a direct replacement, but I've never actually seen one. Older rebuilt iron A6's were so unreliable that they coined the term "black death" to describe how they deteriorated and failed internally. It sounds like maybe the parts numbers above are a newer A6 model that is more reliable. After my first rebuilt A6 failed I paid for a shop to make new barrier hoses, and switched to a Sanden and brackets from Vintage Air. Its a lot smaller form factor.

As you make the conversion, if you have a 2 groove water pump pulley, take a look at Rock Auto and see what options you have for PS belts. My truck has the HD cooling option, and you can use a longer PS belt that goes over the crankshaft, water pump and PS pump. This means you have 2 pulleys driving the water pump, and if you lose one of them you will still have an operating cooling system.

Bruce

R134a is not miscible with mineral oil, so that was a recipe for disaster. The aftermarket always recommended POE oils for conversions, but interestingly, no OEM would guarantee compressors when POE was used.

The term 'black death' was more often used with the Ford FS10 compressor. The Teflon coating on the pistons slowly sloughed off, leaving the most awful goo through out the system. It has come to be thrown around for lots of A/C failures, but it had a very specific origin. It was not easy to clean up either.
I'm surprised to hear anyone claim an A6 was unreliable. They will stay lubricated and running even with an empty system (also like the old, single cylinder York/Tecumseh and RV2). They were so far ahead of their time (the NVH of the York/Tecumseh and to a lesser extent the RV2 were awful in comparison), and so superior in operation and durability, they were not only used by GM exclusively from 1962-1975, but also in Mercedes Benz, Rolls Royce, Jaguar, many heavy equipment manufacturers and some Fords.
Like so many things, GM threw out the baby with the bath water with the R4 compressor (never branded as Frigidaire, but as Delco Air, Harrison and finally Delphi). I'm still shocked Delphi bragged about the Scotch Yoke design on their website. That it is why they are so noisy!

I was intrigued by the Pro6Ten compressor when it appeared. I haven't any experience with them, but would suspect they are good. With the supply of rebuild-able A6s (I wouldn't buy any rebuilt compressor) drying up (forget what year they were last built, sometime in the 80s, IIRC), there was apparently a need, as so many were fitted in vehicles and equipment originally. Besides the labor (and skill) to replace the front seal in a functioning A6 is cost prohibitive.

 

[da_raabi]

This is some awesome info guys, much appreciated!

My compressor is a new (not reman) Advance Auto brand (ToughOne) model that says it is pre-oiled. Should I drain it and add the total correct amount of oil, or leave it be and add a few ounces more based on the above recommendations?

What PAG oil should I be using? I was at the parts store looking at what they had, and there were several weights available.

Is R134 all created equal, or should I stick with some sort of brand? There seems to be huge price differences between store brand ($7.99 for 12oz) and other brands ($30+ for similar quantities).

Should I add a dye? If so, how much?

Last question, and this one is weird. I purchased all new hoses and lines, but the solid line I got that connects the evaporator to the condenser (that has the port on it) appears to be for a suburban. It has the extra connection on it just before the pressure port. Unfortunately this was the only replacement part I could find for this line. My question: can I cap off that connection, and if so - what would I use to do so? Does anyone have any experience capping off a Suburban rear A/C?