How to Pull Vacuum for A/C Re-Charge
 

I have a quick one that I hope someone can answer. I recently had the R-134 drained to have some engine work done. Everything is back together, but I have no fluid in my AC system.

What is the easy process for adding R-134 back? I have topped off systems a bunch of times in the past. I was told I should pull a vacuum first. What is the easy way to do this, and is there anything I need to consider before doing this myself?

Thanks.

Start the engine and then use the engine to pull a vacuum on the a/c system, this is what I did the last time I charged up a system.

Small amounts of air and/or moisture will really interfere with the performance of an A/C system. Engine manifold vacuum will not pull a low enough vacuum to do it right. There may also be a health hazard. I tried this once with R12 and I noticed a strong odor from the exhaust. I read somewhere that the stuff in the exhaust was toxic cyanide. I don't know if that is correct but I am not sure that using engine vacuum is a great idea. You can sometimes clear air out of the system by purging the system - add some R134 (maybe run the compressor for a few seconds) and then discharge it. Then charge it again. If there is any moisture in the system, the purging method probably won't work.

If you lost refrigerant then there must be a leak.
If the leak is not fixed and you pull a vacuum you will pull air and moisture into the system.

I recommend finding the leak, most likely in the schrader valve packing or the shaft seal. Once the leak(s) are fixed you can pull a vacuum. Typically you would use a vacuum pump to pull the system into a vacuum. Then recharge with the proper pounds of refrigerant.
:flag:

It should be done with a vacuum pump. The engine doesn't create enough vacuum to remove all the air and moisture from the system otherwise. Also, when refrigerant burns, it decomposes into some nasty things.

Burnt refrigerant turns into Phosgene Gas.

What phosgene is
Phosgene is a major industrial chemical used to make plastics and pesticides.
At room temperature (70°F), phosgene is a poisonous gas.
With cooling and pressure, phosgene gas can be converted into a liquid so that it can be shipped and stored. When liquid phosgene is released, it quickly turns into a gas that stays close to the ground and spreads rapidly.
Phosgene gas may appear colorless or as a white to pale yellow cloud. At low concentrations, it has a pleasant odor of newly mown hay or green corn, but its odor may not be noticed by all people exposed. At high concentrations, the odor may be strong and unpleasant.
Phosgene itself is nonflammable (not easily ignited and burned).
Phosgene is also known by its military designation, “CG.”
Where phosgene is found and how it is used
Phosgene was used extensively during World War I as a choking (pulmonary) agent. Among the chemicals used in the war, phosgene was responsible for the large majority of deaths.
Phosgene is not found naturally in the environment.
Phosgene is used in industry to produce many other chemicals such as pesticides.
Phosgene can be formed when chlorinated hydrocarbon compounds are exposed to high temperatures. Chlorinated hydrocarbon compounds are substances sometimes used or created in industry that contain the elements chlorine, hydrogen, and carbon

I know R-22, chlorodifluoromethane, decomposes to phosgene, as well as other things, such as hydrochloric acid, and I also know firsthand that it isn't a pleasant thing to be around, nevermind inhale. I'm not sure exactly what 134a becomes though.

Chris

Thanks everyone. The system doesn't have a leak. It was drained to do some engine work. I was just curious what I need to do to make sure that it is charged back correctly.

As for phosgene, that is pretty nasty stuff. I worked in a polycarbonate plant and phosgene is a precursor used in the manufacturing process. The COCl breaks down pretty quick, especially inside human lungs. It reacts with H2O to produce HCL (hydrochloric acid) and carbon monoxide. Needless to say, the reaction in human lungs is similar to case of pneumonia, except instead of filling with water, it is hydrochloric acid. The posters are correct, it is pretty nasty!

I just wanted to make sure that I am going to do the right thing to get the A/C back up. I don't have a vacuum pump, but I do have the R134. I'm guessing this will be something simple to go to any A/C shop and tell them what needs to happen. I just wanted to make sure I do this right. Thanks.

:iagree:
General hazards: Compressed liquefied gas. HFC 134a is not flammable in air under ambient conditions of temperature and pressure. In laboratory test, under conditions of high pressure, HFC 134/air mixtures were shown to be flammable. In general, for the test equipment used, at temperatures up to 170 deg. C., flammable mixtures were only produced at pressures greater than 50 psia, and with more than 50 volume % air. Mixtures of HFC 134a should not be used for pressure or leak testing. Thermal decomposition will evolve toxic and irritant vapors

A little different but same toxic results

:flag:

If I have the cans of R134, can the vacuum pump be rented easily? I just don't know how to ask a shop, "Hey, I have the fluid, how much will you charge me just to add the refrigerant while you put it under vacuum?" Is this something I can do easily at home?

I guess my question is how to put it under vacuum. I can easily find the high and low pressure taps, but neither of which are remotely close to vacuum pressure. I know this must be simpler that I'm making it, but what am I missing?

Thanks.

I believe you can rent a vacuum pump. If you know anyone who does refrigeration work they should be able to help you out.
If you opened the system and just bleed the refrigerant to the atmosphere without capping off the lines then there is probably moisture in the system. A new dryer strainer may be needed as well. it is not that complicated to do if you have the equipment. You do not want air entrained in the system.
Bottom line:
If it were me I would have the dealer do the job.

http://www.deadly134.com/

I'm not exactly sure what was done to release the refrigerant. I know why they did it, but I'm just not sure how. I spoke with them today, and they said it was just simple to pull a vacuum to make sure no moisture got into the system. The compressor won't run, and they said it's fine as long as the compressor doesn't run with it in it's current state.

The shop is about 110 miles away, and I only have this week left for vacation. I didn't want to spend a chunk of my vacaton time chasing this if a local shop can do it. Would you just bring this to a local shop and have them do it? I wasn't planning to change anything. I was hoping they could simply pull a vacuum and add the refrigerant. Is that not possible. :cheers:

I was not trying to frighten you out of doing it but only to point out the potential dangers.
Any place that does auto refrigeration should be able to do the job.

:flag:

No problem. I'll need to get to a vacuum pump anyway, so they might as well do it all. I just wanted to make sure they understand my situation before beginning. They should be able to knock it out. Thanks.

If you have a medium to large size air compressor, you can use an inexpensive jet ejector type of vacuum pump. These are available at Harbor Freight Tools and other places for $20 or so. I have used one for years and had no problem with operation of the A/C.

If you have a CH air compressor, can you configure a hose to the air intake of the compressor to pull vacuum? If it's strong enough to compress 100 psi, can it draw as much?

How much vacuum do you need on the AC system before filling?

:bigears

Not sure if it could pull that much vacuum or not, but I would think it may be damaging to the compressor, as it may rely on the airflow through the cylinder to keep the head cool, and when pulling a vacuum I think this cooling ability would diminish significantly. I know that our refrigeration vacuum pump gets quite toasty when it's been running for awhile, but the entire pump section is also submerged in oil. As far as how much vacuum, it seems or cars the recommendation is to leave the vacuum pump on the system for 30-45 minutes, which I would guess would put you between 20-30 inHg of vacuum.

Chris

:iagree:
If you use an air compressor inlet you could pull compressor oil up through the piston rings through the sump. They are not designed for Vacuum.

If you have an old refrigerator pot you can use it to pull a vacuum.

A couple questions.
When the refrigerant was removed was the system pumped down?
If all the refrigerant was removed from the system,was the compressor oil removed too?

:flag:

I haven't done it yet but I need to remove a hose and replace it with a longer one. It's the hose on the compressor. I'll probably take it to a shop for the evac and replace the hose at home and take it back for a recharge. I'll just need to price it out now.