I know this!!
Hopefully I got to you in time!!! STOP running your A/C! Good? Ok, don't panic. I did exactely what you did last summer. Kids were cooking and I felt bad. So I moseyed on into my local AutoZone and saw that cool can with the bear and "55% Cooler" and even had the cool little pressure guage. Something like $50 and there it went into my low side. Blew ice cold for something like a day and then nothing but hot. Then after about a week there was this godaweful ringing sound from the engine bay, sounded like a bell. Turned out to be the compressor pully banging around on my clutch. Didn't find out til about a couple of months ago what I did. I over pressurized my A/C and burned out my clutch!. So.....if you want to do it right, keep reading....
....still there?
Ok, first off, those cans of 134a shouldn't be sold to anyone because average joes like myself could go buy one and fry our a/c, costing $100's, if not $1000's in damage. It's wrong, and they should be stopped. End of story.
Here's what needs to be done:
First, the entire system needs to be visually inspected for damages and leaks. Leaks can be detected using a range of devices, but my preference is a handheld just because it's easier to manuver around. Basically they're just little sniffers with a flexible tube. Some can be had for fairly cheap, but I can't vouch for reliability. There's also UV detector lights, but there's no saying wether or not the refigerant in your system has UV dye in it. Obviously if there's in leaks, further inspection is necessary to determine whether it's residue or actual leakage, hence why I also prefer the sniffer.
If that's complete, the entire system needs to be evacuated. It need's to be hooked up to a machine that can recover both refrigerant, oil, and any other contaminants in the system such as air and water. Both those last two are a big no-no, I'll get to why in a minute. The system needs to be draw into a vacuum. I believe Dodge says the 1500 a/c for my own truck says to draw down the system for a minimum of 45 minutes.
....Vacuum? Ok...lets get sidetracked for a moment....
We can all agree that atmospheric pressure is 1 atmosphere/14.7 psi at sea level, and WATER boils off at 212 farenheight. If you go up in altitude, the pressure will reduce and water will boil off at a lower temperature, and visa vera if you decrease altitude. Now, how does this apply to R134a?
R134a boils off at about -15 F, and water freezes at 32 F. This can understandably create some issues inside a closed loop system as ice crystals will form and clog the system, causing intermitent cooling. Moisture in the system can cause a whole other mess of issues, such as corrosion. So, by vacuuming down the system for an extended period we can 1) lower the pressure to boil off moisture and remove all contaminates, and 2) leak test the system. If you vacuum down the system and shut down the pump, and the gauges show no loss of vacuum, viola! you have an enclosed system that is ready for charging!
Next (the easy and exciting part), charge the system. Ensure to messure the amount of oil that was removed during the recovery process. The exact amount of NEW oil needs to be put back into the system. Most machines will give you the option to choose how much to inject. Choose the correct amount of refrigerant to add. For example, my truck takes 2LB 2OZ. After charging, it's time for the performance test. Run A/C at max, fan high, engine running. Your looking for your LOWEST and HIGHEST pressure readings on both the low and high side guages. Rule of thumb to remember:
LOW SIDE (Blue Guage): FOT (Fixed Orfice Tube)=22-48 PSI
TXV (Thermal Expansion Valve) OR
H-VALVE (Expansion Valve Block)=10-30 PSI
The easiest way to determine which type of metering device you have is by figuring out which type of device you have. Follow your small diameter line from the compressor, this is the high side/high pressure line. It will first lead to your condensor which is located on the front of your radiator. It will typically go into the top of your condensor and then come out the bottom. From there it will either go into a Reciever/Drier (Big cylindrical canister) at which point this is a TXV/HVALVE system, or it will go straight into the firewall. If there is no canister after the condensor, you can follow that line with your fingertips until you feel several small dimples in the line. This is where your FOT is located. Typically though, the portion of the tube where the FOT sits is wrapped by some insulating material.
HIGH SIDE (Red Guage): AMBIENT Temp multiplied by 2.42=Lowest PSI allowed
(AMBIENT Temp multiplied by 2.4)+50=Highest PSI allowed
So, an example: My truck, FOT system. Low side reads at 28 PSI, 78 degrees out, so highside should be 78*Fx2.42=186 PSI, and (78*Fx2.4)+50=237 PSI. The low and high guages stay within those ranges during the compressor on/off cycle, and the A/C blows COOOOOLD!
So, if you performance test your system, and it's not blowing in the correct ranges, then further diagnosis is required. And that, my friend, shall be left for another night.
Now....because I just wrote you a mini-novel, my advice to you: Go ahead and make a buddy with an A/C shop. There's a reason those guys get paid. Even with that knowledge I still put out $120 only because I don't own the equipment that tends to be VERY expensive. I'm sure there's other ways to evacuate and leak test a system, but I havn't learned those yet.
Good luck buddy!
