a/c Freon pressure specs

[Oh2quick]

Im glad to hear it went well for you........How did you go about assuring you only had .98 lbs of freon or did you just watch your high side low side pressures till they fell into range?

[swissfrank]

I just measured the low side pressure until i was in between 25-35. The only time that the 1 pound of charge would be any use is only once the AC system was evacuated and vacuumed , otherwise it would be next to impossible to use the 1 pound as a guideline with a system that has remaining charge.

[Oh2quick]

Thanks alot ......Thats what weve always done on the ole homestead and it works fine I fell alot more comfortable now

[Unit107]

I have been watching this post and successfully charged my A/C last night.

It took less than 15 minutes, once I figured out where everything is and triple checked the procedures before proceeding.

I picked up a Charging hose with pressure guage at AutoZone ($20) and a can of r134a ($8).


After finding the Low Pressure valve (photo below shows its location on my '01 4.4i), I started the engine, AC to max, then attached the hose as outlined and pressure read about 20psi.


I then turned the knob to begin the flow of r134a into the system and it immediately jumped to about 35-40psi (slightly greater than half of the good range on the dial, which is 25-45psi).

I let it sit for a few minutes, and the needle did not move. I check the AC inside the cabin and it was blowing cold. I removed the hose and replaced the valve cap and am happy to say I drove to work in comfort this morning.

My assumption is that, when connected properly, the hose and can of r134a become an extention of the closed AC system, and the system only takes what it needs to bring the psi up the the required level. From a product usage standpoint, it seems as if it barely took any r134a from the can, but the results were a 180 from what I was experiencing from my vents just minutes earlier. From reading other posts on this topic, it sounds as if the theories are correct that it does not take much of a loss of refrigerant to throw off the system.

I will let you know if my 95 degree+ drive home from work this evening is anything but "cool".

[Oh2quick]

Thank you for the input.......and IM glad to hear of another successful job . However after all the input I've recieved on this forum and a few phone calls I've made I feel obligated to throw this out there for your consideration. I too have the typical handy dandy r134a kit and upon reading the generic instructions on the can I would say you hit your marks perfectly .....but being privy to some info shared with me from weasel56 & and a local bmw tech I must at least mention to you that our bmw's have a smaller threshold than some vechicle s described in the instructions on the can .Basiclly what Im saying is that I fear that the 45psi on the low side may exceed where you need to be. I have been told that it doesnt take but being low just a smidge to make your a/c hot. Therfore it stands to reason it wouldnt take much to put it into overcharged and possibly cause you compressor trouble down the road.
Im not making any allegations or accusations I just dont want you to be in a situation where you say "I wish someone would have told me" I fully intend to do the very same thing you just did the very same way. The only exception being Im gonna use my manifold gauges cause I trust my gauges more than the ones that come with the r134a and Im only going to charge till the low side reads between 25-35 (based on the best info I have recieved up to this point) It is my understanding that to go above 35 could put you in a state of overcharge. However I dont know the ambient temp and other varibles that existed when you did yours......... you could be spot on.
Im just throwing it out there for your consideration because I would feel terrible if a couple of weeks from now I read a post that you mysteriously lost your a/c compressor. Then again it could just be my paranoia creeping in again lol Best of luck

[swissfrank]

the compressor has a blow off valve if the pressures do get dangerously high, there have been people on this forum that have had this happen, and the valve has opened to vent the excess presure. Their systems were well over charged and all that was needed was to evacuate the system to bring it back into normal operating pressure again.

If you add 1 whole pound of r134a to a system that has not been evacuated and with an exisiting charge it will surely be over charged. Add enough for it to be within 25-35 psi on the low side with the compressor running on MAX, and you'll be fine, with no issue.

If you really are worried, pay for the piece of mind and take it to a professional.

[Oh2quick]

Thank you Swiss.... Im not worried at all.... I feel like Ive gotten really good information and facts so I have no reservations about taking this on. I was just a little concerned (some call it a characther flaw) when unit107 said he had charged his to 45 and I had information in my possesion that told me that might not be advisable. I just wanted unit107 to be informed. Yourself and others all have said that 25-35 is a good working range so thats where I ll be..... and I do appreciate all the input

[Unit107]

When I initially read the guage before introducing the r134a into the system, it was reading just shy of 20psi. The guage, unfortunately, is generic, with the "Safe" range indicated as 25-45psi, which I assume is somewhat of an industry standard when it comes to A/C systems.

After introducing the r134a into the system, it immediately jumped to barely over 35psi(the width of the guage dial over the halfway point of the 25-45psi range). With the setup I used to re-fill r134a, there was no way to "force" additional product into the system.

After reading some of your comments here and thinking about it for a while, it is quite possible that several factors came into play (air temp around 85 degrees, accuracy of the guage being slightly off, etc.). I feel fairly confident that the vehicle took what it needed, and that it is reading the appropriate level at this time.

I guess that only last few questions I would have to feel more confident about this adventure are: Are my assumptions correct about the system absorbing the necessary amount of r134a from the can, based on the system I used to refill? And also, if the range is 25-35psi, as perscribed by the manufacturer, what are the negatives of having the system pressurized to exactly 25psi or 35psi, versus being in the middle at 30psi on the nose? If it is that touchy, will I find the compressor sitting in my lap while crusing at 90mph with the A/C at MAX when the pressure is at 36psi(again, if the guage used was 100% accurate)?

I think this discussion has been very valuable(at least to me), as some posts seem to stop short in stating you can do something on the cheap, but don't go into the details on how it should be done properly and what pitfalls others might have encountered while making the fix. Hopefully this will be valuable to anyone looking to take this challenge on.

[Oh2quick]

Im not really sure about the system taking what it needs part........ but I know I feel better now that I know there is a pressure relief or pop valve on the system. I also dont know what the exact results of overcharging the system is , and I hope we dont find out Im going to defer these questions to weasel and swiss frank they are far more knowledgeable on this subject than I .
I do agree on the part about some post not being talked through at length and covering all the bases ,but I think we have about covered all the bases on this one if not .......anyone please feel free to comment

[Oh2quick]

o.k heres wheres we are at in the saga . I put the gauges on the x today I pulled the x in the garage last night just started it up. It will blow cold cold air on start up gauges show 36 low side and 250 high side ..welll im thinking thats bout right so I drive it down the road bout 2 miles about a mile into the trip passenger side is hot, middle is hot and drivers side is cool , rear is cold so we pull into the gas station aux fan is running fine . Now the only confusing thing is the control in between the air vents (red dots and blue dots) It does not feel like the wheel goes into position when I try to put it at 3 blue dots but if I hold I can feel the temp get cooler . How is this control operated is it cable, relay or air Im thinking this is my problem but not sure anyone got some info along these lines ? i hate to assume its fsr I have nothing to make me believe it is unless Im missing the symptoms , but Im really not exactly sure what the fsr does , if anyone would like to take a stab at explaining that , it would be appreciated.