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.
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Edited: Tue December 01, 2009 at 7:39 PM by pippo
You can find the information here
copy and paste any approved refrigerant you use requries different unique fittings and is explaned in this article.
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.
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.
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.
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Edited: Thu December 03, 2009 at 7:55 AM by pippo
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.
OK, I think I found it now....:
Thats it, right guys?
beware of the arrival
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.
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.
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.
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?
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Edited: Fri December 04, 2009 at 4:06 PM by pippo
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.
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
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.
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.
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