A/C Charge by Myself

-
harrisonm

harrisonm

Well-Known Member
Joined
Jan 16, 2005
Messages
5,744
Reaction score
8,012
Location
Topeka, KS
I was wondering about charging My AC system by myself. I have a vacuum pump I use for brake bleeding and gauges that will allow me to add R134. I have a 69 Barracuda with a Classic Auto Air unit that had to come out for paint. It is all back in now and ready to charge (yes I replaced the drier and all O-rings). Why couldn't I just vacuum the system down as much as possible and put R134 in myself. It isn't so much the expense; I just hate to drop my car off and go back to pick it up later. the few places I have called basically said just drop it off and we'll call you when it is done. I was thinking on putting in about half the charge with the AC compressor off, and then finishing the charge with the motor and compressor running. Thoughts?
 
You need a good vacuum pump. I have no idea what you have, but if it's made for brake bleeding, it's HIGHLY unlikely to develop enough vacuum. You need to know how much refrigerant to put in. So you should have documentation on that. If not I'd contact the manufacturer. When charging, you want to get as much in "to start with" as possible. I always start out an empty system by liquid charging into the "high" side port. The compressor valves will prevent liquid getting into the cylinder. The liquid will "flash" through the system all the way around to the low (suction) side. Once this bleeds "in" then you can start the unit and finish charging CAREFULLY into the low side. Be darn sure you don't get any/ too much liquid into the low side of the system

You have a proper charging manifold? You need a way to monitor appropriate temps. A "good" system will have charts, temps and pressures to cover typical operation. You want LOTS of air past the condenser. If at all possible you want a "great big fan" into the front of the radiator.

You can download manuals for some of the Classic Air stuff from their site.....

Classic Auto Air - Air Conditioning & Heating for 70’s & Older Cars & Trucks.

This says only that 24 oz of R134 is the charge

http://www.classicautoair.com/manuals/1-1062Manual.pdf

They do warn that after initial charging, BEFORE engaging the compressor with running engine, that you HAND TURN the compressor 15-20 revolutions This would be to ensure there is no liquid that is "hydraulic lock"
 
Last edited:
harrisonm said:
I was wondering about charging My AC system by myself.
Click to expand...

I can't recommend it. If you don't know what you're doing (for real, not just following step-by-steps in a book) it's much too easy to hurt yourself badly. It's also very easy to cause immediate and/or time-release expensive damage to your A/C system.

I have a vacuum pump I use for brake bleeding
Click to expand...

No, sir, that is not even close to adequate. Wrong kind of vacuum pump. You need the big motor-driven kind.

and gauges that will allow me to add R134
Click to expand...

Do you know how to interpret the readings on the gauges, by themselves and relative to each other?

Why couldn't I just vacuum the system down as much as possible and put R134 in myself
Click to expand...

Because your brake bleeding pump won't pull anywhere near a good enough vacuum. You'll be left with noncondensibles (air and water) in the system, which will form acid that will gradually eat your condenser, evaporator, and other parts from the inside out.

It isn't so much the expense
Click to expand...

If you can afford to have it done right, by someone correctly using the right equipment, do it!
 
DIY vacuum pump from an old fridge. Will pull 27" Hg. Not mine but I have same pump on bench waiting for a day of brazing fittings on it.
vacuum_pump_b.jpg

DISCLAIMER >>> this was just an experiment, No one is going to recommend doing this<<<
I know the acid issues but I did my Breeze with a mighty vac (no kidding, took me like 20 minutes of pumping) and a can of propane. the A/C condensor O-rings were bad so I replaced them. The system had already vented so I decided to see if I could actually pull a vacuum and hold it, sure enough it did. so then I popped the might vac connected to the makeshift hose that was cut off an old R-134 recharge can off the low side connector and chucked the same hose to the end of a propane torch with a pipe clamp (Sanford and Son music in the background) and attached to low side connector. I then started the car and turned the A/C on which didnt energize the pulley becasue there was no pressure in it. I turned the valve on the torch and in about 3 minutes, the A/C kicked on! I kept filling it until the disposeable fill can valve told me to stop. Darn thing was blowing pretty cold air again! I scrapped the car soon after but I wonder how long that would have worked...
 
Well, thanks. That answers my question. I am a pretty good mechanic, but I just might leave the AC work to the pros. The Goodyear store down the street will do it for under $100.
 
pishta said:
DIY vacuum pump from an old fridge. Will pull 27" Hg. Not mine but I have same pump on bench waiting for a day of brazing fittings on it.
vacuum_pump_b.jpg

DISCLAIMER >>> this was just an experiment, No one is going to recommend doing this<<<
I know the acid issues but I did my Breeze with a mighty vac (no kidding, took me like 20 minutes of pumping) and a can of propane. the A/C condensor O-rings were bad so I replaced them. The system had already vented so I decided to see if I could actually pull a vacuum and hold it, sure enough it did. so then I popped the might vac connected to the makeshift hose that was cut off an old R-134 recharge can off the low side connector and chucked the same hose to the end of a propane torch with a pipe clamp (Sanford and Son music in the background) and attached to low side connector. I then started the car and turned the A/C on which didnt energize the pulley becasue there was no pressure in it. I turned the valve on the torch and in about 3 minutes, the A/C kicked on! I kept filling it until the disposeable fill can valve told me to stop. Darn thing was blowing pretty cold air again! I scrapped the car soon after but I wonder how long that would have worked...
Click to expand...

OMG!!!

Propane will cool, but your driving a death trap. Can you imagine a leak, in the engine compartment, while driving, or haveing an accident? Crispy Critters.
 
weebull said:
There's no propane in that old fridge pump. They work great.
Click to expand...

Not talking about the pump. Talking about charging the system from a propane torch.

PS: that pump will remove the air, but will not pull a deep enough vacumm to remove moisture.
 
Yes, it is foolhardy to charge an A/C system with any kind of hydrocarbons (propane, butane, mix of the two, etc). Also, fuel-grade propane is full of contaminants, including lots of moisture. The filter-dryer will immediately be saturated and rendered useless.
 
Charrlie_S said:
Not talking about the pump. Talking about charging the system from a propane torch.

PS: that pump will remove the air, but will not pull a deep enough vacumm to remove moisture.
Click to expand...
Oops! I must have read that post three times and missed the part about the propane torch. an evap leak would be very flammable.
 
The use of a refrigerating compressor is not really right, but if you make sure it has enough oil in it, pull 27 inches of vacuum, turn it off, see it hold that vacuum overnight, then run it another hour or two, it will pull the moisture out.
I made my own a long time ago, back when I built an AC system for my house.
I sealed the tubing ends and used clamp on line piercing access ports to have real Schrader fittings to use with a manifold gauge set.
Propane in an AC system scares the hell out of me. I hate fireballs in my face.
Never do this please.
 
Well even traditional refrigerants are "flammable" because they have oil aspirated throughout the system. And the older refrigerants, ammonia, methyl chloride, and sulfur dioxide were certainly not "human friendly." LOL

All the traditional Dupont refrigerants, R11/12/22/500/502 etc, produce deadly phosgene gas when run through a flame, so they are not exactly inert.
 
I used a Mitey Mitey pump in the past, now HF pump. Duracool works for me. Read more, no fears. R-134A is to be outlawed.
 
Last edited:
harrisonm said:
I was wondering about charging My AC system by myself. I have a vacuum pump I use for brake bleeding and gauges that will allow me to add R134. I have a 69 Barracuda with a Classic Auto Air unit that had to come out for paint. It is all back in now and ready to charge (yes I replaced the drier and all O-rings). Why couldn't I just vacuum the system down as much as possible and put R134 in myself. It isn't so much the expense; I just hate to drop my car off and go back to pick it up later. the few places I have called basically said just drop it off and we'll call you when it is done. I was thinking on putting in about half the charge with the AC compressor off, and then finishing the charge with the motor and compressor running. Thoughts?
Click to expand...
As the others stated, a brake bleeder vacuum will not do it. Ideally, one would wish to evacuate the system to 500 microns or less. That would equate to more than 29.9 inches of vacuum. That is some serious suckage and most typical shop recycler machines will not do it, nor are the analog gauges accurate enough to determine a precise reading. It needs to be evacuated to boil all the moisture out, otherwise it will not work at the most efficient level. Moisture in the system is not condenseable and if enough exists it can actually freeze at the expansion valve when the refrigerant undergoes a endothermic reaction as it changes from a liquid to a vapor state.
 
I'd be worried that installing a new dryer without pretty darn immediately sealing and evacuating the system would load the dryer with moisture very quickly.
 
I recently did mine with the help of an HVAC guy in the neighborhood. He has a large electric vacuum pump that pulled 30 inches in about 10 minutes. He used his manifold gauges and knew what he was doing. He also ran nitrogen through to test the pressure and vacuumed it out before we added Freon.

This is a guy I happen to see in the neighborhood and just stopped to BS with and found out he has an AMX (and a parts car). I asked if he would give me a hand on it. I offered him some money but he wouldn't take it.

I'm a pretty good mechanic but don't know A/C for squat!!
 
In the old days, shade-trees would fill w/ R-12, then blow some off to sweep out air and moisture. That was in the days of 25c Freon cans and Freon BB machine-guns. Seemed to work and the filter's dessicant probably captured any remaining H2O. Certainly pumping down to 29" Hg w/ a Mighty-Mite hand pump is better than nothing, especially on a hot day w/ engine in the sun. You can get half-way there by connecting to intake manifold vacuum (best after a booster charcoal filter & check valve), using a valve to isolate. R-134A is much more problematic w/ moisture since PAG oil absorbs it and forms corrosive acids. PAO 68 oil is a better choice, more efficient and works w/ all refrigerants. Seems silly to convert to R-134A today just before it is outlawed. You can vent HC refrigerants (Duracool, Enviro-safe) w/ no more danger to the earth than a cow fart, but the EPA says that is illegal because ... "just is".
 
BillGrissom said:
Seems silly to convert to R-134A today just before it is outlawed.
Click to expand...

Don't let's be alarmist. R-134a is not going to be outlawed. It's going to be phased out of use in new systems, and at the same time its production is going to be phased down. That doesn't mean it's going to become illegal to use, or unavailable—keep in mind you can still get R-12 and you can still charge an R-12 system with it, even 22 years after R-12 usage in new vehicle A/Cs was stopped.
 
Propane in an A/C system??? Oh the humanities. Can you imagine having a flammable substance under your hood right next to the system full of another extremely flammable substance known as gasoline??? OMG!!!!!!!!!!
 
I always charge from the low side. Pull a vacuum for a good 30-45 minutes to get the moisture out of the system. Switch from the vacuum pump to the 30# can, purge a little refrigerant into the charging lines and then crack open the low side. I have a digital scale so I like to weigh in as close to what's called for, and then watch the gauges. If you're having issues getting enough gas into the system, you can always blow some heat on the side of the tank, or if you're using 12 oz cans, submerge them in a bucket of hot water. On a 75 degree day, you should see the low side about 28-34 and the high side anywhere from 170 to 220 depending on how much air is moving across the condenser. It ain't exactly rocket science.
 
rednesss said:
Propane in an A/C system??? Oh the humanities. Can you imagine having a flammable substance under your hood right next to the system full of another extremely flammable substance known as gasoline??? OMG!!!!!!!!!!
Click to expand...

Hurr hurr hurr. The fuel system was designed to store and transport flammable fluid, and it keeps that flammable fluid on the other side of the firewall. The A/C system wasn't and doesn't. Haw haw haw. Hurr hurr hurr. Think, McFly!
 
Last edited:
rednesss said:
I always charge from the low side............ It ain't exactly rocket science.
Click to expand...

And that is exactly backwards from what I was taught. What you do is, you dump "a bunch" of charge into the HIGH side before you fire up the system. This gets the major part of the charge into the system, and yet, because it races from the (just past) compressor, through the condenser, and all the way around to the low side, there is almost zero chance of any liquid gettting into the compressor.

THEN you start the system and charge in the last of the gas into the low side, either CAREFULLy charging SMALL amounts of carefully metered liquid, or "gas only."
 
A) A 30 lb can of refrigerant has the tap on top and only lets out gas. In order to worry about getting liquid on the low side and slugging the compressor, you'd have to turn it upside down. B) The pressure coming out of the 30 lb'r is way less than the pressure you will see on the high side line, so it would just pump it back into the cylinder if you opened the valve. The low side will see around 25-35 psi, the pressure out of the cylinder is somewhere around 70 psi depending on outside temp, so by hooking it up to the low side, it sucks it in and is forced in by the pressure differential. But to each their own.
 
Sorry but you are incorrect. The pressure depends on whether the cylinder or the cylinder has liquid inside, AKA "saturation" and the TEMPERATURE. You can't turn the cylinder upside down? really?

And then there's this, ??WHUT??

" The pressure coming out of the 30 lb'r is way less than the pressure you will see on the high side line, so it would just pump it back into the cylinder if you opened the valve."

I don't even know what that is supposed to mean. So I will explain. AGAIN. LISTEN CAREFULLY

YOU START with the system evacuated and SHUT OFF. Repeat. You start with the system evacuated and NOT RUNNING

You do whatever you do, charging cylinder, scale, etc, and get the target amount set in your mind. Get the manifold connected, fittings and hoses purged, etc.

Then with the cylinder CONFIGURED FOR LIQUID, you dump the MAJOR PART of the charge USING LIQUID, into the HIGH SIDE FITTING. To repeat for the FOURTH TIME you do this with the system NOT ENGAGED, SHUT OFF, NOT RUNNING. The liquid will flash clear through the condenser (repeating) the dryer, the control device, the evaporator, at which time THERE WILL BE NO LIQUID and the building VAPOR PRESSURE will start to BUILD PRESSURE on the low side gauge

After this has settled down, you will have a SAFE condition to START the system. You will have MOST of the charge in the system, the refrigerant will be VAPOR at the compressor inlet, and now all you have to do is run the system and make final adjustments to the charge.
 
You must log in or register to reply here.
-

Back
Top