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skreem
07-11-2005, 10:47 PM
a little background info
i put in a new condensor and charged the system myself. the can said to hold it upside down while charging to charge the liquid. yesterday the a/c worked and it was about 35 psi on the low side. today it wasnt working so i checked it while it was off and it was 140 psi.

now my questions.
1) is 140 psi normal for an a/c that's off?

2) i never had the system vacuumed after i installed the new condensor, does that make a big difference?

3) did i charge the system properly with the can upside down or was i not supposed to charge with liquid?

thanks for any help you can give

oneof81
07-12-2005, 08:39 PM
1) is 140 psi normal for an a/c that's off?

No.......unless it is 112 degrees F where you are.


2) i never had the system vacuumed after i installed the new condensor, does that make a big difference?

You bet!! If you don't evacuate the system, what we call "non-condensibles" get into the system. Non-condensibles is simply put, air. When you add air to your A/C system, (I realize you didn't add it yourself, but when your system was open to the atmosphere when your replaced your condensor, a lot of air got in) you are just adding pressure to the system making it work harder. Worse than that, you have also added moisture, which was in the atmosphere to the mix. The moisture will mix with the refrigerant and make acid which is not good. Another thing water will do is flow along with the refrigerant and when it comes to the expansion valve, it will turn to ice and restrict the flow, or even block all flow of refrigerant.


3) did i charge the system properly with the can upside down or was i not supposed to charge with liquid?

First of all I am going to assume that you are using R-134A? If that is so, then, yes, you need to charge with the can upside down......BUT........YOU MUST BE VERY CAREFUL if you are charging on the low side!!! You can run the risk of slugging liquid refrigerant to the suction valves of the compressor,ruining them! It has to be metered in slowly if you are adding it to the low side. Here is the proper proceedure:

After repairing the system (and changing the oil to PAG if you retrofitted to R-134A from R-12) and sealing it, evacuate the system to 500 microns . Once you reach this micron level, continue to evacuate for five more minutes. At this time, isolate the vacuum pump from the system and allow the pressure to rise on the micron gauge (you need a micron gauge to do this properly). If the pressure rises rapidly to atmosphere, you have a leak! You then need to find the leak, fix it, and start all over again. If the pressure rises rapidly to 1500 to 5000 microns, you still have moisture present and it is sublimating. If this is the case you need to un-isolate the vacuum pump and pump once more to 500 microns and then continue to pump for 5 minutes longer and re-try this procedure until you can isolate the vacuum pump to the system and the pressure rises no more than 1500 microns in 5 minutes of time. When you get here, you are ready to charge the system. Hopefully, since you have a micron gauge, you will have the proper gauges to connect to both high and low sides of the system. If you have a four valve manifold, you should have been pulling the evacuation on your charging hose at the same time. If you have only a two valve manifold, you will have to purge refrigerant from the can to the high side fitting to make sure you have no air in your hoses, so that you don't introduce more air from the hoses into the system when you start charging. Remember the vacuum we have been pulling to get all the air out of the system? We don't want to add some after we just got it all out. You can them charge liquid into the highside of the system. If your system takes 2.5 pounds to charge it and you only have 1 pound cans, you will need to purge each time you add another can. So if for instance, your system DOES take 2.5 pounds, and you have just added two cans, you can fine tune with the final can on the low side. But you have to be careful. Since you will be adding liquid refrigerant to the low side, you need to meter it very slowly until you reach the proper charge.

What is the proper charge you ask? Good question. I really can't tell you what your gauges should read when you reach the proper charge if this car had been retrofitted from R-12 to R-134A. The best way I can tell you is to MAKE SURE that you don't overcharge the system! Venting refrigerant from the system is illegal and could cost you a LOT of money if someone sees you do this and they call the EPA!! So find out how much refrigerant your system used with R-12 and start at about 70% of that before you start charging on the low side. Put an accurate digital thermometer in one of your vents, put the A/C on as high as you can, idle the car at about 2,400 rpm or so, and add little by little until you can get close to 55 degrees exiting air temperature. If you can get close to this, you are very close to optimum. Don't try to shoot for 50 thiniking that it 55 is good, 50 is better. It is VERY easy to overcharge the system this way and you will be doing yourself no favors overcharging your system!

If your car is new enough that it is supposed to take R-134A and you are lucky enough to have a charging cylinder or an accurate scale, you can actually "weigh" the refrigerant into the system and you will not have to take the time to fine tune the charge. Good luck!

Punisher
07-12-2005, 09:05 PM
Take the car to a garage.. Unless you have R134a gauges and vacuum pump... Which I assume you don't.

I have R12 gauges and vacuum pump.. which sucks ass since my celica was retrofitted before I bought it to R134a.. Stupid ass new fittings.

Btw, Oneof81 got it dead on.

skreem
07-12-2005, 10:27 PM
i took it to my mechanic today and he vacuumed and recharged the system. its much better now. blowing 45 degrees farenheight, does that sound about right?

Punisher
07-13-2005, 02:51 AM
Sounds damn fine.. They must have a hell of a vacuum pump there to do the job so quickly.

skreem
07-13-2005, 03:30 AM
how long does it usualy take?
it took about an hour for the whole thing or maybe a little more then an hour.

alltracman78
07-13-2005, 03:47 AM
That's about right...

Punisher
07-13-2005, 05:14 AM
Hmm I guess.. I'm objective to it though.. They probably have a real powerful vacuum pump that's why.. But anyway my objection is the fact that it can take hours and hours even a day straight to remove ALL moisture.

oneof81
07-13-2005, 12:11 PM
It might take an hour..........might not. Depends on the amount of moisture in the system. But they were undoubtedly helped by the fact that you had charged the system. They had to "recover" the old refrigerant before evacuating the system. Refrigerant is highly hygroscopic. That is to say, it attracts moisture like a sponge. So a lot of the moisture could have been removed when they recovered the old refrigerant, thus allowing for a short evacuation. However, they probably just "winged" it and pulled the evacuation for 45 minutes or an hour and said, "that's good enough". LOL. Micron gauges (accurate micron gauges) are expensive, so most automotive techs don't own them. I'll bet if you asked him how far down he pullled it into a vacuum he would respond 29 or 30 inches. It is impossible to pull a system to 30 inches on earth. The compound gauge (low side gauge) measures from 0 pressure to 30 inches of vacuum, indicated, as well as positive pressure. But the vacuum side of the gauge is really just an indication that you are in a negative pressure situation. It is FAR to innacurate to give a good reading of the vacuum. If you took the last inch of negative pressure (from 29" to 30" with 30" being an absolute vacuum) and divide that last inch of vacuum into 29,400 divisions, each of those divisions would be one micron. The lower the pressure, the lower the temperature that water boils off at. That is the REAL reason for evacuation..........to remove the moisture, the non-condensibles (air) are secondary. Water boils at one atmosphere (760,000 microns) at 212 degrees.....at 200,000 microns water boils at 152 degrees.........at 50,000 microns water boils at 101 degrees.......at 10,000 microns water boils at 52 degrees..........at 500 microns water boils at -12 degrees. So you can see that if you can evacuate your system to 500 microns and hold it there for 5 minutes and the ambient temperature is 80 degrees.......you really should not have any moisture left in the system. The trouble with using only the low side gauge to tell when you are done is that it is so inaccurate. When it is showing 30 inches of vacuum (which would be 0 microns) a micron gauge would show about 200,000 microns. Chances are your system is fine though (moisture free), but I would bet they didn't use a micron gauge. PAG oil is extremely hygroscopic and if there were substantial amounts of moisture present, it would take several hours for a good vacuum pump to remove all the moisture. They don't have that kind of time and don't want to charge you that amount of money so they just evacuate for an hour and say "we're done." It's called the SWAG theory..........Scientific Wild Ass Guess......LOL! That's all you can do if you don't have a micron gauge.

Punisher
07-13-2005, 05:10 PM
I once read on a refrigeration forum that a guy claimed he actually GOT 30" of vacuum during a severe thunderstorm... Who knows.

If I have any doubt that there is moisture in a system I will let the vacuum pump run for a day straight..

Ya know Skreem shoulda really put a new filter/dryer in the system too.. because that way atleast if there was any moisture or acid the dryer would've picked it up. Typically the best thing to do on a hermeticly (sp?) sealed system anyway.. I would always just slap a big ass dryer on instead of vacuuming the system for a day... lol.

oneof81
07-13-2005, 09:57 PM
I once read on a refrigeration forum that a guy claimed he actually GOT 30" of vacuum during a severe thunderstorm... Who knows.

I believe he got an indicated 30"...........but you cannot achieve this except in space.

Ya know Skreem shoulda really put a new filter/dryer in the system too.. because that way atleast if there was any moisture or acid the dryer would've picked it up. Typically the best thing to do on a hermeticly (sp?) sealed system anyway.. I would always just slap a big ass dryer on instead of vacuuming the system for a day... lol.

Always a good idea on a hermetically sealed system.........easy to do on a refrigeration system or a split system A/C unit or even a large package unit.........not real easy to do on a car........especially an All-Trac.

http://home.covad.net/~billprice/smilies/driving.gif

Punisher
07-14-2005, 12:12 AM
Well I don't see it being very hard on our Celica's... I just did the dryer/filter on my moms Accord and that wasn't really hard.. Jeez I had the evaporator out and all..

In any case I always get "indicated" "30 or better! Gotta love those gauges lol.

oneof81
07-14-2005, 12:23 PM
Well I don't see it being very hard on our Celica's... I just did the dryer/filter on my moms Accord and that wasn't really hard.. Jeez I had the evaporator out and all..

But I'm talking about when you said a "big ass drier". Only so much room there. But I guess it all depends on what your definiton of big ass (http://img298.imageshack.us/img298/4812/bigass7po.jpg) is! You won't be able to fit that one there!!


http://home.covad.net/~billprice/smilies/pissinthesnow.gif

Punisher
07-14-2005, 04:34 PM
oh no.. I ment big ass on a sealed system.. on the car just get the factory replacement..

spacepiston
07-17-2005, 06:46 AM
a little background info
i put in a new condensor and charged the system myself. the can said to hold it upside down while charging to charge the liquid. yesterday the a/c worked and it was about 35 psi on the low side. today it wasnt working so i checked it while it was off and it was 140 psi.

now my questions.
1) is 140 psi normal for an a/c that's off?

2) i never had the system vacuumed after i installed the new condensor, does that make a big difference?

3) did i charge the system properly with the can upside down or was i not supposed to charge with liquid?

thanks for any help you can give


1) It is normal for the pressure to be well above 100 psi on a hot day for an a/c system that is off with the refrigerant levels balanced on both sides. It might be a bit high but nothing I would worry about. 35psi on the low side is a bit low and you probably won't get good cooling. You should have 45-65 depending on the system and the temperature. The do-it-yourself gauges usually have a helpful chart or marks on the gauges to help you determine the proper charge. I charged my grand prix today. It had 30 on the low side and I had to add about 20 oz. of refrigerant to get it blowing nice and cold. I think the guages read somewhere around 50 psi at that point while running.

2) Not vacuum pumping the system means you have moisture from the air in there. Is it bad? Sure. Is it going to kill your compressor? Doubful. Will you have higher pressures? Maybe a little, but there isn't much you can do w/o a vacuum pump accept put a new filter dryer on and call it good.

3) Don't worry about "slugging" the compressor with liquid refrigerant. Yes it helps to charge with liquid because it's faster. Does it really matter if you charge with the can right side up or upside down? No. Not unless you are in a big hurry. If you have oil charge in the can or leak stop you might want to tip it upside down otherwise it may never get into the system. Always charge from the suction side/low pressure side. Aftermarket recharge kits have the quick connect fitting which singles this port out, so not to worry.



No need to be anal retentive when charging/converting/repairing your a/c system. I went to school for hvac and I've been working in the field for 4 years now and I know all the refrigeration theory, all the possible problems that moisture causes, mixing of refrigerants, pressure this, pressure that. Yes it matters, but for the average automotive a/c system for the average joe, it really doesn't matter. Buy a $4 can of recharge with leakstop and hope for the best. (assuming you converted your toyota with the slightly more expensive conversion kit. Works great on my car 2 years now).

Punisher
07-17-2005, 07:32 AM
I think this post as already been well covered :)

Could always go to an appliance repair shop .. pay 20 dollars for a used compressor and use it as a vacuum pump :)

Personally I don't believe anyone that isn't an A/C tech should be screwing with this shit.. I'm sick of all this fail-safe shit.. these different valve sizes piss me off so much.. Just so idiots can do their own A/C.