Air Conditioning Tech Thread.

[Rhyno]

I wrote this in the thread "Aircon for AE82" but thought I would repost it here since it is relervant, and someone may find it beneficial in regards to pressure and vacuum testing.

"As you have mentioned in the AC thread, a lot of auto ac shops only have a vauge idea of what they are trying to acheive, and have educated the general public into believing that "Air cons run on gas, and she just needs a top up". To be clear a refrigeration or airconditioning system should only require refrigerant being put back into due to neccesary work where the refrigerant had to be removed or there was a leak that was repaired.

Any system with a thermal expansion valve (TXV) over time will equalise, as the TXV valve will allow refrigerant to pass through so when the system restarts it doesn't need to push against full discharge pressure to get away. You can still have liquid and vapour in diffferent parts of the system, and their are exceptions but this is correct as a generalisation. So you will get pressures inside your evaporator that are up near 300 psi which is 2068.42 kpa (i work in kpa) after some time, espically on a hot 30+ degrees day.

My point is that as an auto ac shop perspective it is more profitabile and acceptable to just regas a leaky system which will keep buissness coming back and the customer walking away happy their AC is cold for 3 months, and they only had to pay$150, instead of $500+ for full pressure test, leak repair and regas.

It is good practice to pressure test as triptek has mentioned, as it will identify leaks helping to prevent money and time being wasted, at a pressure at least equal to the pressure the refrigerant will put on the system.

Vacuuming checking does work but how the hell do you determine where the leak is? Feel all over? Wait for some soapy water to get sucked in then have dry the system out, plus repair the leak? A vac test is ment to confirm your pressure test, and that you have removed contaminants from the system (oxxgen and moisture mostly)."

Kind Regards,

Ryan

[matty12]

. So you will get pressures inside your evaporator that are up near 300 psi which is 2068.42 kpa (i work in kpa) after some time, espically on a hot 30+ degrees day.

Kind Regards,

Ryan

You mean condensor dont you??

I dont know why some people only vac test when the system doenst even run in a vacuum at all, a pressure test is the only way, and the pressure you test at would veary depending on the year of the car. Old stuff can handle 300psi if you tested a late model that has a very thin design evaparator it wont hadle that much as it never ever run that high, the most it will see is standing pressure on a hot day, maybe 90-120 psi. You could possible blow the evap with that much pressure in it.

[Rhyno]

I was talking about the Condensor.

I thought that may be the case, I had mentioned that in the "AC for my AE82" that evaporators in domestic fridges are the same, and cannot be tested above their running pressure as they may pop.

So a pressure test to 90 -120 psi is the way to go for new cars, and you can go higher with old school mobiles. Cheers for that, I mostly have played around with old gear.

Thanks again Matty12

[matty12]

I test old stuff to 300psi easy, no worries at that pressure but late model would be less around 200psi.

In fact was testing most stuff to 300 until a recent a/c course suggest less than that for newer stuff.

[Z2TT]

Old and New stuff while true you cant generalize, apparently the old Merc W124's were notorious for leaky evaporators, all depends on how good the evaporator is, I think in general heat exchangers in lots of cars aren't designed that good, but more for cost cutting.
So pressure testing is kind of a risk as you never know what to expect but personally I would say 150 PSI just to be safe.

Usually do guys watch the pressure reading to see if it drops, or can there still be a leak even if it is not detectable via pressure drop.... so do you use a UV light. Reason is for evaporator leaks if it's a small
one it probably wont register on the gauge or will it?

When you guys do leak testing how do you go about it, do you use a refrigerant for leak testing or just Nitrogen?, was wondering if you use Nitrogen you can't use a sniffer to detect small leaks.

[matty12]

different for me as im using R134a, its very controlled so you cant use the gas to find leaks. just test with nitrogen bang it on a pressure, let the pressures equalize between high/low normally bout 5 mins or so then turn the bottle off. I let stuff sit for a minimum of 1hr, any drop is considerd a leak and will be found or not charged. While on test go over with soappy water to check and then walk away.

If i have a vehicle overnight, i will let it sit on about 150psi and check in the morning. If its all good on vac for a hr then charge up.If something comes in with no gas, theres no visual signs of a leak and pressure test ok it get glo leak in it to find the problem next time.

When testing though its all done at ambient temps so its possible that the cools and the heats may open something up that wont leak on nitrogen.

[Z2TT]

The thing is if leaving it overnight, wouldn't the pressure of the nitrogen inside the system change as the ambient temperature outside changes, which if the day is colder the next day.... may fool one into thinking it's a leak?


Also is there any refrigerants your "allowed" to use for leak testing, so you can use a sniffer.

[matty12]

Im not sure if sniffers wprk on other stuff,you can use it on a system that still has gas in it. I have one but ive never used it.

[maccac__1590]

im sure i heard or read somewhere at tafe but i think they reckon that if you know there is a leek and the system is empty and you have pressure tested it and still cant find it than you can charge it with gas and dye to so to find the leek, but you have to recover it straight away and fix the leek

[Z2TT]

Yeah well the sniffer will be the only way to go on leak spots that are hard to see example the condenser coil, you won't see the dye on the leak spot so you'll have to use a sniffer to detect the small amounts of gas escaping from the leak in the core, but wouldn't it be kind of hard as it's hard to poke the leak detector around there in order to get it to detect it right at the leak?

[maccac__1590]

yeah sniffer would be the go, for that sorta stuff unless you can see the core, its a pain in the ass but we make up fittings and blanking caps and remove the core (evap or condencer) and hook it up to the air compressor and dunk it in water

[Z2TT]

Yeah.

I was thinking of an idea for a sniffer, they should design one with a small tube that you can poke around, and a fan that sucks in air through the tube into the sniffer, that will save lot's of trouble especially with cars where it's hard to get access, saves time too.

Evaporator leaks on the other hand are pretty easy to find if the refrigerant has a good dye in it, as the gas builds up in the housing overnight, when the fan is started the next day you can notice a bit of the smell.

[dnegative]

Whats the deal with using hychill over R134a?

I'm told it will be as cold as r12?

[CrUZida]

Hychill (HC12) is a non-ozone destroying version of R12.
So you don't need to 'convert' an old system to run on it.

R134A needs 'converting' to be used in an R12 system.
Although 99% of places will just install fittings to the system so that you can't regas it with R12 accidently.

I spoke to my aircon guy a while back about HC12, and he said that he's seen many different products come and go over the years that were replacements for R12, and so far R134A was the only one that seems to be sticking around. So based on that he doesn't deal with HC12.

[dnegative]

Because most of the systems around are designed for r134a, problem is I think it doesnt work 100% in systems designed for R12.