Automotive Air Conditioning Information Forum (Archives)

Provided by www.ACkits.com

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Are quick disconnect fittings for R12 compressor a good idea? Pages: 12Last

pippo on Tue December 01, 2009 7:36 PM User is offline

Hi Guys,

Im getting ready to check pressures/possibly add R12 to a system, and wondering if I should screw on the 2 little fitting/adapters that allow one to use the quich disconnect feature typical with R134a hoses. One thing that bothers me: you have to be sure the fitting does not cause a slow leak. Id rather maybe loose a tad of gas when unscrewing and be sure of no faulty fitting, instead of having the adapters installed just for the convenience of a quick disconnect/apparent "saving" of that tad of gas, and actually risking loosing MORE in the long run.

Thanks, Men.

-------------------------
beware of the arrival

Edited: Tue December 01, 2009 at 7:39 PM by pippo

Spector on Tue December 01, 2009 8:46 PM User is offline

You can find the information here
http://www.epa.gov/ozone/snap/refrigerants/macssubs.html
copy and paste any approved refrigerant you use requries different unique fittings and is explaned in this article.

NickD on Wed December 02, 2009 7:37 AM User is offline

I miss those good old Scharder valves, easy to repair with a new valve stem, and don't have that large surface area of the quick couplers that never seem to reseat properly after depressed causing leaks. Besides what you are proposing is illegal. OE's pushed the quick couples to save a couple of pennies in production to boost the stock value.

pippo on Wed December 02, 2009 8:08 AM User is offline

Quote
Originally posted by: NickD
I miss those good old Scharder valves, easy to repair with a new valve stem, and don't have that large surface area of the quick couplers that never seem to reseat properly after depressed causing leaks. Besides what you are proposing is illegal. OE's pushed the quick couples to save a couple of pennies in production to boost the stock value.

Thaks, Nick. I figured that those things are more trouble than they are worth. I wont mess with them. Last thing I need is to add a potential leaky valve . No wonder they are illegal. Thanks, Man!

-------------------------
beware of the arrival

Cussboy on Wed December 02, 2009 9:00 AM User is offline

I'd also chime in with: don't bother. Like: how many times do you think you'd really need to use your gauges to check pressures? If the system operates fine after your repair, don't touch it until/if it later malfunctions.

"Never trouble trouble until trouble troubles you" - Mel G.

pippo on Thu December 03, 2009 7:49 AM User is offline

Quote
Originally posted by: Cussboy
I'd also chime in with: don't bother. Like: how many times do you think you'd really need to use your gauges to check pressures? If the system operates fine after your repair, don't touch it until/if it later malfunctions.



"Never trouble trouble until trouble troubles you" - Mel G.

Exactly. Thanks, Man. Oh, while we're at it, theres supposed to be some sort of chart here showing ideal pressures vs ambient temps and the like. I'll search for it. Just in case I cant find it, I will ask for maybe some direction.........

Tanks!

-------------------------
beware of the arrival

pippo on Thu December 03, 2009 7:54 AM User is offline

OK, Im already in trouble as I found a chart but not sure what the numbers are for. For example, it shows at about 79 deg F (about ambient here right now in FL), PSI for R12 should be about 70.2 ????? Somethings not right...... Im thinking thats not the right chart for me ...........Heeeeeelp.

-------------------------
beware of the arrival

Edited: Thu December 03, 2009 at 7:55 AM by pippo

HECAT on Thu December 03, 2009 10:29 AM User is offline

A pressure temperature relationship chart (P/T), provides the vapor pressure characteristics of a given refrigerant at a given temperature. R-12 would produce 70.2 psi at 70 F, 77.0 psi at 75 F, and 84.2 psi at 80 F. This would be the pressure in a refrigerant container or the static pressure of a charged system. Hope this helps.

-------------------------



HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

pippo on Thu December 03, 2009 2:59 PM User is offline

Quote
Originally posted by: HECAT
A pressure temperature relationship chart (P/T), provides the vapor pressure characteristics of a given refrigerant at a given temperature. R-12 would produce 70.2 psi at 70 F, 77.0 psi at 75 F, and 84.2 psi at 80 F. This would be the pressure in a refrigerant container or the static pressure of a charged system. Hope this helps.

I am still kinda lost, Hecat. Are you saying that this "70.2 psi" is what one should expect the low pressure gauge to read when testing/charging a system? I understood that psi should be in the range of more like 35-40, depending on ambient........I know its me, what am I not seeing?

-------------------------
beware of the arrival

pippo on Thu December 03, 2009 3:45 PM User is offline

OK, I think I found it now....:

http://www.ackits.com/aacf/ptchart.cfm

Thats it, right guys?

Thanks!

-------------------------
beware of the arrival

HECAT on Thu December 03, 2009 5:05 PM User is offline

Yes those charts show some generic ranges of low side and high side pressures of an operating system at given ambient temperatures.

The pressures I was referring to is the static pressure temperature relationship of the refrigerant itself.

-------------------------



HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

TRB on Thu December 03, 2009 5:19 PM User is offlineView users profile

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=21372

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

pippo on Thu December 03, 2009 7:27 PM User is offline

Quote
Originally posted by: HECAT
Yes those charts show some generic ranges of low side and high side pressures of an operating system at given ambient temperatures.



The pressures I was referring to is the static pressure temperature relationship of the refrigerant itself.

OK, thanks hecat. So, how would these static pressure values actually be of practical use if say, one is charging a system? Why would one need them? Just need to learn, thats all........

-------------------------
beware of the arrival

mk378 on Thu December 03, 2009 9:41 PM User is offline

When you first check out a car and connect the gauges with the engine off, finding the pressure is less than the static pressure you know that there is almost no refrigerant in the system. Other than that, static pressure and pressure temperature charts aren't used for much. When you have a factory system with the original refrigerant type, always charge it by weight.

NickD on Fri December 04, 2009 5:27 AM User is offline

For every different refrigerant, you have a different P-T chart, for R-12, if you have a good old fashion POA system that actually regulates the low side pressure at 28.5 psi, the expanding refrigerant would have a temperature of 30*F that gives you nice cool air without freezing. Due to the thermal conductivity between the refrigerant, the stuff that actually gets cold, the evaporator may only go down to about 33-35* F, the trick is to get the lowest low side pressure without the evaporator freezing up. Lower pressures actually produce lower vent temperatures.

What all vehicles have in common is the state the vehicle has to be in when checking low side pressures, namely AC on, blower at maximum, one vent open with a thermometer stuck in it's mouth, doors open so the AC is working, and the engine running between 1,500-2000 rpm. Depending on the type of system and the ambient temperatures, that is really where the low side pressures will vary. Typically at 85*F ambient with R-12 with medium humidity, another factor, you shoot for around 30 psi. But this is vehicle specific. With a TXV system, that pressure tends to hold at around 30 psi even with ambient temperatures approaching 100*F where with a CCOT system that low side can go up to 65 psi. At 65 psi, the expanding refrigerant temperature would be according to the P-T charts about 65*F, really not very good. When you need the maximum cooling as possible with higher ambient temperatures, can't really get it with a typical CCOT system. You may tend to charge low with a hot ambient with a CCOT system to get better vent temperatures, but it the ambient temperature drops to 70-75* F, you system will cycle like crazy wearing the hell out of your clutch and compresso, darn thing accelerates from zero to engine speed in under a second, lots of wear and tear.

Good old shop manuals like Toyota and Honda actually give you the ideal low side pressures at varying ambient humidity and temperature conditions. Most domestic manuals tell you to charge by weight and hope for the best not even touching on this key subject. One rule of thumb at a 85*F temperature is an attempt to have pure liquid flowing into the evaporator as foam doesn't cool very well. Such systems install a sight glass so you can see with your eyes if you have a pure liquid or foam. But at colder temperatures, you will see foam, and if you go by the sight glass at cooler temperatures, you risk blowing out your system at higher ambients. In a good system with a high pressure cutoff switch, it simply cuts the system off, but if you are constantly cycling your system with high, high side pressures, again causing excessive compressor wear, and not getting much cooling.

The first step in charging by pressure is a thorough cleaning of the AC systems, any debris buildup in the condenser or the evaporator or poor operating fans will really mess up your pressure readings, pressure readings depend on a like brand new system which basically translates to a clean system. This is not easy to do as it sounds as some evaporators are totally inaccessible, Ford comes to mind with the heater core and evaporator locked up tight in a box where the rest of the car was built around it. Have to take the car entirely apart to get at that box, then remove it and take it apart.

You cannot ignore the resulting high side pressures, typically with a good R-12 system at a 85*F ambient, should range from 220-250 psi. Brother-in-law gave me one of these DIY kits, he purchased it, but decided not to use it. First thing I noticed, not getting real R-134a, has some kind of unknown sealer in it, wouldn't put that in if my life depended on it. But not my life, but the life of my system. Second thing I noticed is that cheap low side pressure gauge, I checked it, was 7 psi off, way the hell too far off for accurate pressure readings, and definitely no high side gauge with this kit, last thing I observed, with that cheap plastic port attachment, almost impossible to install it without leaking out half the refrigerant in your system. I have no idea why the EPA permits this garbage to be put on the market unless they want people to blow up their AC systems.

You can charge a POA or a variable displacement compressor system with the help of gauges, but this requires a great deal of skill and experience that comes with years of working on AC systems. I really cannot recommend this, it's far better off to charge by weight like the manual says you should. Just too many variables in these systems that toss your gauge readings way off.

I don't know if this helps or not, but can say this, the less you know, the more equipment you need to do it right. A charging station would be nice if not completely necessary.

HECAT on Fri December 04, 2009 8:58 AM User is offline

Quote
Originally posted by: pippo
OK, thanks hecat. So, how would these static pressure values actually be of practical use if say, one is charging a system? Why would one need them? Just need to learn, thats all........

Understanding the p/t characteristics of a certain refrigerant are important for design engineers. It is needed to understand and predict how a certain refrigerant will react within a system; i.e. when it will boil off (gas) and when it will condense (liquid) in relation to the pressures, vacuum, and temps being applied. Other than understanding what relative static pressure should be at any given ambient temp; this information will have little bearing on how to properly charge a system.


-------------------------


HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

pippo on Fri December 04, 2009 4:05 PM User is offline

Thanks, MK, hecat and Nick, for the detailed post. Man, the more you learn the more you realize how little you know.

Since we are now onto this, let me explain more details.....Of course, it is R12, the car is an Alfa Romeo 87 spider with Sanden 508 compressor. The ac is running well, blowing cold, and I suspect may be nothing required at all, BUT I thought I should at least check pressure (on low side?) just in case , assuming one can tell if all is ideal and the car is NOT needing some R12.

Thats all Im trying to do as it is running well, although, on hot sumer days, I have some doubt as if it could be any colder but hey, its a cloth top convertyible, you know.

Anyway, whattya think? Should I just put the gauges on the valves andf check for pressure and report back Guys?

Thanks, Men!

-------------------------
beware of the arrival

Edited: Fri December 04, 2009 at 4:06 PM by pippo

HECAT on Fri December 04, 2009 4:16 PM User is offline

If the A/C is working well and blowing cold, I would leave it alone.

Pressures are used to diagnose and verify system performance, and do not tell you if the charge amount is correct; this is done by weight.

-------------------------



HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

pippo on Fri December 04, 2009 4:30 PM User is offline

Quote
Originally posted by: HECAT
If the A/C is working well and blowing cold, I would leave it alone.



Pressures are used to diagnose and verify system performance, and do not tell you if the charge amount is correct; this is done by weight.

Thanks, Hecat, again. But I dont get it, if one has a hunch the system might be underpoerforming, and hooks up gauges, and finds say, pressure is off, doesnt that point to maybe some leaked out R12? I mean, once you charge system its too late to know afterward how much is left in there, right? Isnt it immpossibl;e to know how much weight is in there 3-4 yrs later?

PS: Alfa spec says charge with 1.54-1.76 lb. 14.5-36.2 psi. when "electromagnet of compressor disconnects".

-------------------------
beware of the arrival

pippo on Fri December 04, 2009 4:33 PM User is offline

Manual also says "below 14.5 means low freon, above 36.2 too much"........so, how DO you add freon IF it is too low then (scratching inside corner of left eye, puzzled)

-------------------------
beware of the arrival

HECAT on Fri December 04, 2009 4:56 PM User is offline

Pressures out of spec can always mean more than just the refrigerant charge is off.

Topping off is a guess. The desire to do so is usually driven by a loss of cooling because of a leak; you said this one is cooling.

Proper way is to recover and recharge by weight.

-------------------------



HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

pippo on Fri December 04, 2009 5:49 PM User is offline

Quote
Originally posted by: HECAT
Pressures out of spec can always mean more than just the refrigerant charge is off.



Topping off is a guess. The desire to do so is usually driven by a loss of cooling because of a leak; you said this one is cooling.



Proper way is to recover and recharge by weight.

OK, now I get it. makes sense. Thanks for the lesson, hecat.

I have no real reason to suspect a loss of R12. I may just pop the guages on there to see pressures for curiosity, but will not "add" gas.

have a good Friday, guys.

-------------------------
beware of the arrival

Edited: Fri December 04, 2009 at 5:49 PM by pippo

NickD on Sat December 05, 2009 5:56 AM User is offline

Quote
Alfa spec says charge with 1.54-1.76 lb. 14.5-36.2 psi. when "electromagnet of compressor disconnects"

It would sure help me to know what kind of system this Afla has, suspect it may have a TXV system with a sight glass as more typical with foreign vehicles. That I know in a hurry just by opening the hood, hard to do that over the internet.

Low side pressure range of 14.5-36.2 psi is huge, only one given psi within that range is optimum but that also varies considerably with the ambient temperature AND the humidity. In like manner the weight range of 1.54-1.76 lb is large, typically on USA domestic cars, they give one weight, but let the low and high side pressures vary all over the place. This again is not the optimum charge for the system, but the reason they do it this way, written for the dealer where optimum ambient temperates and humidity do not occur on a day to day basis. Optimum conditions are 85* F and 50% RH, so easier just to print an average weight, no two AC systems are identical in volume with production tolerances.

If you know what you are doing, can do a much better job of reaching optimum charge levels with pressures along with several other factors, if you don't nor can take the time due to shop hour weights, better to charge by weight and call that close enough.

I have a feeling you have one of those very inaccurate plastic combination low side only gauges where you can attach a can to that are only available for R-134a for the reason why you want to install an adapter. Very bad idea, you risk losing your very valuable R-12 charge, and if you do attempt to add more refrigerant, risk adding air to your system. And always a bad idea not to look at the high side pressures while pressure charging, as I said, these kits should be outlawed as you can blow up your system.

Also being a 1987, you have got to have debris buildup in your system, air conditioning can also be written conditioning air, and if you don't have proper air flow that would also vastly affect your pressure readings. These manuals assume you have a brand new vehicle that never left the showroom.

pippo on Sun December 06, 2009 7:49 PM User is offline

Quote
Originally posted by: NickD
Quote
Alfa spec says charge with 1.54-1.76 lb. 14.5-36.2 psi. when "electromagnet of compressor disconnects"



It would sure help me to know what kind of system this Afla has, suspect it may have a TXV system with a sight glass as more typical with foreign vehicles. That I know in a hurry just by opening the hood, hard to do that over the internet.



Low side pressure range of 14.5-36.2 psi is huge, only one given psi within that range is optimum but that also varies considerably with the ambient temperature AND the humidity. In like manner the weight range of 1.54-1.76 lb is large, typically on USA domestic cars, they give one weight, but let the low and high side pressures vary all over the place. This again is not the optimum charge for the system, but the reason they do it this way, written for the dealer where optimum ambient temperates and humidity do not occur on a day to day basis. Optimum conditions are 85* F and 50% RH, so easier just to print an average weight, no two AC systems are identical in volume with production tolerances.



If you know what you are doing, can do a much better job of reaching optimum charge levels with pressures along with several other factors, if you don't nor can take the time due to shop hour weights, better to charge by weight and call that close enough.



I have a feeling you have one of those very inaccurate plastic combination low side only gauges where you can attach a can to that are only available for R-134a for the reason why you want to install an adapter. Very bad idea, you risk losing your very valuable R-12 charge, and if you do attempt to add more refrigerant, risk adding air to your system. And always a bad idea not to look at the high side pressures while pressure charging, as I said, these kits should be outlawed as you can blow up your system.



Also being a 1987, you have got to have debris buildup in your system, air conditioning can also be written conditioning air, and if you don't have proper air flow that would also vastly affect your pressure readings. These manuals assume you have a brand new vehicle that never left the showroom.

Thanks, Nick. I appreciate your concern. I yanked all out of the Alfa 5 yrs ago, and flushed everything. New expansion valve, and comp. Used ester oil. Also, I pressure tested with nitrogen the evap, to be extra cautious. I dont have a cheapy auto zone"kit" hose to charge, but a decent used double gauge manifold set (for R12). I also have adapters to screw on these hoses for R134a in future. Reason for me initially (not any more though) wanted to use screw on adapters onto my R12 comp valves is I wanted to utilize the gauge set for all my vehicles, which I still can, even without the adapters, I learned.

I agree those Alfa specs are wide. Thats alfa for you. Now, if youre thinking "why is pippo so adamant on checking pressures with a good working system", I just got a hunch thinngs are not ideal, as the comp was leaking VERY slowly oil for a few yrs now, and I figure if it leaks oil, it in theory leaks R12 too (?)

Yup, there is also a sight glass on the dryer. But now having ex[plained a bit more, I have a few questions:

1) I looked at a few you tube videos on checking pressure, and they dont make sense. They show hooking up the hoses respectively to high/low side with yellow fill hose left hanging. How is it possible to open up the valves/knobs to view pressures on gauges and not have all the gas escape in to the manifold and out the yellow tube??? I mean, the manifold galleries in there are all open up to each valve, right?

2) For that matter, how does the low side pressure compartment stay separate from the high side if the manifold gallery is open inside? Impossible, Im thinking!!

3) The sanden comp (507 or 508) has 2 valves on TOP, with S and D next to each, AND 2 more valves in the rear facing directly to the rear of car. Why are there a total of 4 valves? I take it the hoses go onto the 2 on top?

That is where Im stuck for now, understanding the guts of a manifold, believe it or not. And how its all open "circuit" inside there, with no apparent prevention of the low side intruding onto the high side, and even escaping out!! Im holding off on doing any damage for now, guys, until I get this straight. Dont want to loose any R12.

Take care!






-------------------------
beware of the arrival

Edited: Sun December 06, 2009 at 8:11 PM by pippo

mk378 on Sun December 06, 2009 8:28 PM User is offline

You check pressures with the valves on the manifold closed. The gauges are always connected to the red and blue hoses and show "live" pressure in each hose. The valves are only opened to charge, recover or evacuate through the yellow hose. With the system running, only the low side valve should ever be opened to charge. Never open the high side valve at all with the compressor running.

The multiple service ports on the compressor are likely duplicates and you can choose either one. If there is a fitting with a large screw cap connecting the car hose to the compressor and also holding the service ports, that is an isolation valve.

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.