Basically moisture from compressed air will destroy a central air system in short order. I personally have never seen one leave a crater, I shire would like to see it.

Mobile systems are more tolerant to moisture, but sweeping the system with nitrogen helps blow out any moisture that was boiled out during vacuum. You really wouldn't think its there, but with a vacuum gauge you can really tell.

Sorry I didn't finish explaining .
I was only referring to what a bad mix AIR is with A/C systems .
An example is AIR/Compressed air being used for a leak check (PREASURISING A SYSTEM) OR flushing a line if that air meets and mixes with the compressor oil . Boom can occur. Always nitrogen, clean safe, inert . added benefit it helps absorb MOISTURE in the system. If a system has been open for a prolonged time or LOW on refrigerant it can run in a Vacuum where AIR can enter , If air enters so does moisture. Only 2 good ways to remove moisture .1 use nitrogen and allow it to stay long enough in the system to absorb, then purge it off. DO NOT run the system with nitrogen inside. 2 A good vacuum . IT Can only be measured with a vac u stat. A good Vacuum is 1000 microns and lower. the ideal vacuum is 500 microns and lower. This unfortunately can not be measured by gauges.
Also remember with car A/C systems that were not designed for 134A from manufacture The condenser just cant do the job properly . Meaning the condenser needs to be a lot larger or the refrigerant charge lower. A poor compromise . TX valves should always be changed if a system changes refrigerant . More flow is required with a LESS yielding refrigerant . High head pressures are MOISTURE in the system, secondly Restrictions. Or a inefficient condenser, Remember also oil migrates around the system with the refrigerant. DO NOT blow it to places in the system where it cant return unaided. Thank you for the link. a good read:) I am new to forums and still finding my way. No disrespect meant for anyone.

Just finished up -- it was either excess oil or a blockage. I flushed the entire high side from condenser to TVX and the evaporator. Replaced expansion valve and receiver drier.

and Success, or about the limit of R134a in my climate!....Definitely either flushed out excess oil or removed any blockage.

I got about 24-26oz estimate in. That is about 6oz short of what the factory manual states, but any higher was outside my comfort zone for pressures. In cooler climates I would have added more for sure. Final pressures 55psi low 375psi high. Ambient temp is 112F. Getting 48F out of the center vents on the quick drive I made. Rises to about 55F at idle. I expect on the freeway it'll get down to the low 40's.

I think that's about the limit of R134a in this climate! Either way it'll last me the rest of the summer and once I put the new evaporator, heater core, compressor RD/TXV and R12 in, I should see even lower vent temps and lower pressures.

Awesome. Thanks for the update.

Congrats! I agree with your assessment regarding the maximum efficiency of your system.

Are you suggesting that the compressor can auto ignite the oil in an a/c system ? or the gas, should you be using propane?

I think you ought to read this :Fuels and Chemicals - Auto Ignition Temperatures

These temperatures listed only exist inside a diesel engine and to start most diesels it is often only with the aid of glow plugs...ie: An ignition point.

I doubt any refrigerant pump can run at these temps'....and where would the ignition point be ?

The 'hole in the ground' sounds spurious.
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I think he may be referring to the danger of oxygen + oil in an oxy-acetylene regulator/tanks setup, where pressures can be in thousands of psi. But we are talking air at 200 psi.

"By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere."

I was wondering if air can be used to do a poor man's "nitrogen" pressure test in a mobil AC system since it is 78% nitrogen. Is there a danger of an explosion with 21% oxygen and refrigerent oil pressurized to 200 psi? Gut feeling WAG tells me no.

Granted, some moisture (relative humidity dependent) will be introduced from ambient air, but since the dryer and TXV will be replaced and the system evacuated afterwards, whatever moisture introduced will be removed.

I vacuum the system for 5 hours or so on vehicles that have been open for some time. Blowing out the system with shop air is okay as long as you purge with refrigerant before charging.

The ox-acetylene sets potential to explode is well known, either due to fire or incompetent handling.https://youtu.be/iam27Mh1zu4



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Holy smoke, that's some fireworks!

What do you use for a vac pump, single or dual stage? What vacuum level do you get it down to? What do you use for a vacuum gauge to see the level achieved?

Single stage commercial . Have calibrated gauge and at 1100 asl I see 29 inches. If you hold 29 for some time and run the engine to full temperature you can be sure that whatever minute amount of water vapor is in the system is absorbed by the desiccant....or so small a volume it will not ice anywhere..


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Would you know if I run two vacuum pumps in series, would I be able to achieve lower vacuum levels than a single pump? I can rent (free) a single stage pump from Autozone, I can scrounge up a compressor from a house AC unit and run that in series.

I need to come up with some kind of digital vacuum gauge. They seem to start at $140 and up. This one reads in microns https://www.amazon.com/CPS-VG200-Digital-Vacuum-gauge/dp/B009AXGCSC?ie=UTF8&redirect=true&tag=gols-20

I don't care the units used. I can convert them Vacuum Pressure - Units Converter

I am buying one of these to play with, $20 shipped New SMC RS Vacuum Pressure Switch ZSE4B 01 26 Q | eBay

readouts in kPa, mm HG, psi and bar

[QUOTE=funola;3608741]Would you know if I run two vacuum pumps in series, would I be able to achieve lower vacuum levels than a single pump? .......................................................[UNQUOTE]

I would say no. Both pumps do the same thing so very low vacuum of 1 torr or better would not be attained. Even lab' rated vac' pumps only pull down to 5 torr.

You need very specialized ( read : Expensive.) equipment to pull a near pure vacuum.

I would say that is is impossible to pull a pure vacuum.


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[QUOTE=dkveuro;3608748]I can have access to a vacuum pump used in a lab, problem is getting permission to wheel my car in there. And then explaining of why I need that sort of vacuum in my car A/C

btw - funola

I have lived in third world countries where resources were scarce, I regularly saw A/C work being done by pressure testing with a junked refrigerator compressor pushing air in the system.

It was good enough - cant say about longevity, usually A/Cs were taxed to the max as summer meant 120F in the shade.

There is no need for scientific grade equipment. A good vacuum gauge as listed above would be swell. Anything that holds under 500 microns is considered a tight system.

Really for automotive systems, under 800 is great.