mechron

AC is really simple once you understand it. it is a closed loop system, here's how it works:

an AC system has a refrigerant, starting at the compressor, the compressor compresses hot gasses and pumps it to the condenser (that thing in front of the radiater). the condenser cools the hot gas back into a liquid, the liquid goes through the reciever/drier (the thing with the sight glass) to remove any water/contaminates. then the refrigerant goes through an expansion valve (or orface) and lets the liquid turn back into a gas. heat is extracted by the liquid evaperating turning back into a gas in the evaporater (that little thing behind the dash). the cool gas then goes to the intake of the compressor and is compressed to a high temprature gas and the cycle start all over.

the important thing about R-12, R-134a or any other refigerants is that they have a direct temprature/pressure relationship. at 250 LBS coming out of the compressor it will be at 250 degrees on the high side, going through the expansion valve at 35 LBS puessure it will be 35 degrees.

there are no designated pressures to look for, the low side will always be between 30/40 LBS, but the high side will vary with the temprature of the day (i've seen as low as 175 LBS on a cool day and seen as high as 275 LBS on a hot day on a full charged system)

refrigerants:
i hate R134a, it doesn't work nearly as good as R12.
R134a is a smaller molicule than R12 and when retrofitting you have to replace all the hoses with the new "barrier hoses" and that is expensive. 62 jeff, you are lucky to have 60 LBS of R12, that should last 2 lifetimes even with a system that leaks a bit. R134a is also corrosive and requires PAG oil instead of the mineral oil all our AC systems came with.
i live in cal and we can't get anything out here because of the green weenies. i have found a great refigerant (FREEZE 12) that i can order online, have shipped to my doorstep. it's cheap, it's a large molecule refrigerant so it doesn't leak out and it cools as well as R12.

JOKE-->62 jeff, don't ever give me your address, i'll come over and break into your garage and steal your stash of R12...

servicing ACs:
never leave an AC system open, get your parts and and replace them and close the system, moisture is your enemy.

ALWAYS replace the reciever-dryer, it cheap and it's like an oil filter--would you ever change your oil and leave the old oil filter on???

ALWAYS suck a vacuun on the AC down to -32 PSI and let it suck for an hour, let it sit for an hour with the valves closed and you don't see any vacuum drop. you probably don't have any leaks.

PS...62 jeff, you can buy those gauges at HF, but don't buy that crappy ventury vacuun pump. i have a blue point (snap on) electric rotary vane pump (it weighs like 15 LBS) and would use nothing less. it is old skool (i've had it for like 25 years) but there is no substitute, check on ebay.

IF YOU GUYS HAVE ANY QUESTIONS, JUST ASK.

62Jeff

Thank you so much for taking the time to put this in print. I'll bookmark it for future reference.

If you break into my garage I'll lock you in until you fix the A/C on all my old cars

32 PSI. Ok, I was thinking we did 32 Inches of vacuum, but that shows you how little I know about those gauges My system ended up with 32 PSI on it for almost 20 hours straight by the time we charged it up. Over 8 of those hours were without the pump running. Wonder what it would do now.

Ok I'll take a look. My friend's vacuum pump was pretty heavy, and made very wet and odd sounds as it ran, but worked great.

mechron

62 jeff, i printed -32PSI but that is a misprint, -32 PSI is 32 inches vacuum. the low side gauge on that gauge set has an inches of vacuum scale that starts at 0 and goes to -32 inches of vacuum. if you want me to explain exactly how to use the gauges when recharging, i can do that.

62Jeff

Thanks for the offer of help on the gauges. I drove the car to a friend's house this morning to do some tuning on the carb of his 66 for him. By the time I got back home I was drenched, and spent, from the lack of A/C in my car.

As for pumps, the Venturi pump I supposed is a Style of pump, correct?

Then a vane pump would be one like this?
http://www.harborfreight.com/cpi/cta...emnumber=98076

mechron

jeff, yes the vane pump is tho one to get, don't even waste your time looking at that venturi pump. my old bluepoint is a rotary vane pump too, only older and WAY larger.

62Jeff

Thanks for the reply. So it sounds like I can go to Harbor Freight and get both the gauge set, and a vane pump like the one I linked, and I'll have everything I need to test and charge my system.

I'm sure I'll be in touch with more questions.

vetzs

Mechron, I for one would like to see a primer on use of the gauge's
Thanks...

Stan's Customs

....just a footnote. In some locations, 32 inches of vacuum isn't possible. I believe the amount of vacuum you can pull varies.. depending on the elevation in regard to sea level of your region.

Stan...

62Jeff

Good point.

I'm at sea level.

david srour

can R12 or the other freon be used in an uncharged R134 system? and if so would this be wise. thankx

Stan's Customs

...I have never tried it...but.

Retrofitting R12 systems to 134A amounts to little more than flushing the system of mineral oil and charging with 134A and one of the compatable oils for that refrigerant. I can't see why it wouldn't work in reverse ...probably real well since R12 is a much better refrigerant.

(I know about the larger valves, tags and in some case hose and o-ring upgrades guys....just trying to keep it simple for conversations sake)

Cheers...Stan

Ron Miller

I'll offer one more tip for some of you guys who may wish you had a good vacuum pump for A/C, but really don't want to invest the $$$$ it takes to buy one given the amount of use you have for it.

A good friend of mine, a few years older, and with a temperament much the same as Duke, was in the automotive repair business for years and years before passing away a few years back. I was having some A/C work done in his shop several years ago, and inquired about the vacuum pump he was using, as it looked a little unusual. He told me it was the compressor off an old refrigerator that he had soldered or brazed an appropriate gage connection fitting to on the suction side. The other side was open to the atmosphere.

I asked how it worked, and he said it worked great. I asked if he wasn't afraid that being used in that manner that it would burn up in short order, and with a little sarcasm he replied, "Hell no, I'm not afraid of it burning up. I've been using it for over 15 years, and it hasn't burned up yet."

I sure do miss him, learned a lot from him and a lot of old mechanics like him over the years. A lot of practical things you learn through life they don't teach in engineering school!!

mechron

OK guys, i was busy yesterday working on my 64 NON AC, non ps, non pb coupe, but i'm back.

VETZS, here's the answer to the use of the gauges.
i started this thread in response to 62jeff's thread here:

http://forums.corvetteforum.com/show....php?t=2039873

the gauge set we were talking about is this one:

http://www.harborfreight.com/cpi/cta...emnumber=92649

use of the gauge set:
the gauge on the right is the high pressure gauge, the left one reads low pressure and vacuum in inches HG. when putting on the hoses this is the correct way, look at the ends of the red and blue hoses, one end will be open and the other end will have a projection that pushes open the schrader valve on the discharge ports on the compressor. the open ends hook to the gauges, red hose to high side, blue hose to low side and the yellow hose to the center port on the gauge manifold.
to hook up the gauge set first close both of the valves on the gauge manifold (look at the link, those are the wheels below the gauges) screw the blue hose to the low side port on the compressor (this will be by the hose coming from the firewall) screw the red hose to the high side port on the compressor ( this will be by the hose running to the front of the car).
to do a recharge open both valves, this will release the refrigerant out of the AC system through the yellow hose. when the AC is empty hook the vacuum pump to the yellow hose (with both valves on the gauge set still open) and turn on the pump. you will hit max. vac. on the low side gauge pretty quickly. ( as stan mentioned, i live pretty close to sea level here in cal and can always pull down to 32in HG, but if you are at a higher altitude like denver you might only pull 24/26in HG). it makes no difference and there is no right inches/HG reading. when i did this as a flat rate mechanic i would run the vacuum pump for 30 minutes, now i do it for an hour. you are basically pulling any moisture out of the system.
after pulling a vacuum on the system close both valves on the gauge set. the gauges will read whether the valves are open or closed) and turn off the vacuum pump and observe the inches HG vacuum on the low side gauge. let the system sit for an hour and then check the inches HG vacuum on the low side gauge, it should be the same, if it drops even a little bit you have a leak.
assuming no leak you are now ready to recharge. tap into your refrigerant can and screw it to the yellow hose, open the valve on the can tap and loosen the yellow hose at the gauge set to purge any air out of the hose. turn your refrigerant can upside down and open both valves on the gauge set. by turning the refrigerant can upside down you are pushing liquid instead of gas into the system, you want to get as much refrigerant into the AC as you can before starting the car. i use the standard 15OZ cans and can get 1-1,1/2 cans in without starting the car. when changeing cans on the yellow hose always close both valves on the gauge set first. with the engine off you can hear the refrigerant flowing through the hoses and also see the readings on the gauges rising.
OK, now you are ready to start the engine and run the AC to finish rechargeing. before starting the engine, CLOSE THE HIGH SIDE VALVE ON THE GAUGE SET and leave the low side valve open, both gauges will still read pressure. now start the engine and turn on the AC. make sure the refrigerant can is RIGHT SIDE UP before starting the engine, this way the ac compressor will be sucking gas out of the can and be compressing it into the system. when changeing cans (for you guys that use the 15OZ cans) just close the low side valve, switch cans and re-open the low side valve.

the gauge readings will be right around 30-32 on the low side and can be anywhere between 175-275 depending on the outside air temprature, the higher the temprature outside the higher the gauge reading will be.
on our old systems charge until the sight glass shows no bubbles. close the valve on the can tap and watch the sight glass for a couple of minutes, if you see a occasional stream of bubbles open the can tap and let the compressor suck in a little more refrigerant until the sight glass remains clear. don't overcharge, the low side gauge will start climbing when this happens and it cuts down on cooling. when charging with the AC on high and a thermometer in one of the vents you should be reading 38-40 degrees coming out of the vent, this is the correct temp for a good AC system. when finished turn the car off, close the low side valve and unsrew the hoses from the car. you will get a little blowby when disconnecting the hoses until the schrader valves close, but it's no big deal.

the nice thing about the older AC systems is if you park the car in the winter and loose a little refrigerant you can just hook up the low side and top it off until the bubbles disappear.

sorry about this being so long but i tried not to leave anything out and wanted to make sure even someone with no experience could understand.

DZVette

"i tried not to leave anything out and wanted to make sure even someone with no experience could understand."

Now we're talkin'! Good thread folks! This one goes in the "how to" collection. When it comes to AC I have no experience unless you count hooking up an old Ford Escort and getting enough R12 into it to get from Florida to Texas without cooking the occupants. That was probably a bad day for the ol' ozone layer!

Thanks!
DZ

62Jeff

This was an excellent summary, thank for taking the time. I've already printed a copy for future reference.

Two questions:
1) How does the procedure differ when using a 30 lb drum of Freon instead of the small cans? I don't remember my friend turning anything upside down or rightside up during the charging process.

2) In my original thread, Powershift had some good advice on testing the current condition of my system. http://forums.corvetteforum.com/show...8&postcount=10
Do you or Powershift know how I would implement those steps using these gauges?

Jeff

mechron

[QUOTE=DZVette;1565723141]"i tried not to leave anything out and wanted to make sure even someone with no experience could understand."

Now we're talkin'! Good thread folks! This one goes in the "how to" collection. When it comes to AC I have no experience unless you count hooking up an old Ford Escort and getting enough R12 into it to get from Florida to Texas without cooking the occupants. That was probably a bad day for the ol' ozone layer!

hey DZ, in addition to being a mechanic i also took engineering, chemestry, physics, astronamy and science classes and read books all the time. i just don't buy all the ozone layer bullpuckey all the moronic politicians and green weenies have been spouting all these years.

while the chemestry is correct there is a fatal flaw in their theory. R-12 is dicloraldifloralmethane, a big molicule. it is much heavier the nitrogen and oxygen atoms that make up the atmosphere and when released into the atmosphere that big ole molicule just falls to the ground. so how the hell do they explain it getting all the way up to the stratospere to destroy the ozone layer????

what a bunch of morons, stupid laws, and green weenie protests and lying to get voted into office they should study a little...
if i had a big hammer i'd be doing this to a bunch of people...

mechron

jeff, not only did i learn AC in college, but when i worked for a chevy dealer just out of school they sent me to a 3 day GM factory seminar on AC, that's where i learned the upside down can trick. it just makes recharging a lot faster and allows you to beat flat rate. you can recharge with your 30LB container upright just fine, it just takes a little longer. i learned the upside down can thing 30+ years ago and that's the way i've always done it.

as for your second question, i've used those leak detectors powershift mentioned, i never had much luck with them. while they will spot a BIG leak or can be useful for checking an evaporater that you can't see in a car they never seem to work on normal small leaks that take a few months to drain or lower a system. i like to inject a UV dye then do a partial 1LB charge and do a check with a black light a few days later (you have 60 pounds of the r-12, a 1LB partial charge shouldn't be a problem). i bought a new UV dye kit off ebay a couple of years ago, it's a mastercool kit, part #53351, it was about $50 as i recall. not only does it come with the AC dye, it also includes the injector, the black light, an engine dye to detect oil leaks and an auto trans dye. i put a little bit of the dye in every system i do.

from what i've read, if you do the compressor and reciever dryer you should be good to go. i think you also mentioned 3 other cars??? i think it would definately be worthwhile for you it invest the small amount to buy the gauges, vacuum pump and a dye kit and do your own work. go to an AC shop and get an estimate, you'll run right out and buy what you need.

one more tip, stay away from the AC sealer all the parts stores sell, that stuff is bad and will ultimately kill your AC.

62Jeff

Actually, I was curious about how to test the pressures of my existing system to see what kind of shape it's in. Is it a matter of just hooking up the high pressure gauge, starting the car, opening the valve, and watching the needle?

Hope so. My dilemma is that a very reputable company (http://www.classicautoair.com/) rebuilt those items for me 18 months ago and here I am again. I'm starting to think that I overtightened the belt in order to get it to stop squeeling, and maybe that killed the bearing or seal.

Yes, 1956 Olds 98 Holiday coupe, 71 Olds Vista Cruiser, 72 Buick Skylark.

Oh trust me, that will happen before this week is out.

Thank you again for your time.

mechron

jeff, to test your system leave the valves closed, just hook up the hoses and the gauges will read. the low side should be around 30LBS, the high side could be anywhere. the best way to check the system is to just look at the sight glass. if you don't want to fix it right now you could just top it off through the low side until the bubbles disappear.

as for your compressor seal, from a previous post of yours as i recall, you said it leaked when you installed it and called them and was told "it has to run for a few hours (9-10???) to seal up. that is total BS, a good seal will be sealed from the first instant. i think you just got a bad job. as far as thinking the belt may have been overtightened causing the leak, it doesn't work like that, you didn't cause the leak by overtightening the belt.

67vetteal

Mechron, Add me to the "Thank You" crowd! On the topic of front seal on the A-6, (Our Comp.), Mitch, from the ACForum.com always recommended the replacement be the Ceramic type. Mitch, has passed sadly. He was as generous as you with his expertise and experiences. I think you would enjoy reading some of his stuff. Ceramic? Al W.