how do you charge auto AC?

masraum · 06-12-2008, 02:56 PM

Late last summer, I tried to get my AC fixed and was told that the repair would be >$1000, so they topped up the system and it was good for the rest of the fall. It's starting to get hot again. I'd like to buy some gauges and top the system off again to get me through this summer. I understand the theory (had thermodynamics and chem in college), but I don't know the practical of how based on temps and pressures. Can someone point me to a link or explain how to charge an automotive AC system using a set of manifold gauges and small cans. My system is R134a.

THanks

Oh Haha · 04:45 PM

Go to the nearest auto parts store and get a can of R134a and a re-charging kit. The kit has the adapters and valves needed to charge the system. [B]Read[/Bs the instructions 2x before starting. It gets pretty wasteful if you screw up and the refrigerant escapes. Oh yeah, it's extremely cold as well so wear eye protection and gloves. DON'T ask me how I know.

Depending on how low your system has gottn, it could take up to 2 cans. They also offer a sealant mixed with the R134a so get that if you can.

Sure, repairing the system properly is the right thing but once you have the kit you can add a can or 2 each time you need to, forever.

Bam!! http://www.aa1car.com/library/ac_recharging.htm

on2wheels52 · on2wheels52's Garage

Is that what we used to call 'suicide kits' at the service station in the so ca desert?
Jim

masraum · 06-12-2008, 05:06 PM

I'm going to get a decent set of gauges, and will top off once or twice, but do plan to eventually fix the leak.

Thanks, I didn't expect the gauge sets to come with instructions. I'm kind of surprised there's not a write up online someplaces, but I guess liability issues keep people from putting instructions online.

Tim Hancock · 06-12-2008, 05:14 PM

Steve, on a somewhat modern car with factory 134, the quick dirty easy method is to buy a couple cans of 134 and a hose/valve combo and after figuring out FOR SURE which is the low side fitting, hook the can up per the instructions, start the car, turn on the AC full blast, actuate the can piercing valve keeping the can right-side-up and refrigerant will start flowing into the system.

-High idling the engine to 2000 rpm while charging helps.

-The can will get cold and the flow will slow as the can pressure drops and system pressure rises. To get the remaining 134 out of the can and into the system, the easiest way I know of and do every time I add 134, is to use a hair dryer to heat the bottom of the can which helps it vaporize and enter the system. This can often take many minutes.

-When the can is empty, (the bottom is no longer cold) close the valve then remove the charge hose from the car's fitting. If the vents are now blowing cold (maybe 40-45 degrees or so on an 80 or so day, call it quits and enjoy, if the vent temps are not cold enough yet (55-60) try adding some more (maybe 1/2-1 can) and check again..... This "normally" will be plenty if your car was still blowing "cool" when you started and just have a slow leak.

The above will "work" often even on an older system that has been down for a long time, but the proper way is to find/fix the gross leak, install a new drier, evacuate the sytem to remove moisture with a vacuum pump, recharge using gages and thermometers to monitor for a proper charge.

I have brought old dead systems to life using proper equipment and I also just often squirt a can in my working but slow leaking systems. I just topped off my daughter's '87 924s and my '92 BMW 325 tonight using the first method I described above (924s took 1.5 cans, and the BMW took one can) both blew barely cool in 85 degree weather last week and now are in the low 40's with a digital thermometer in the center vents).

Dan in Pasadena · Dan in Pasadena's Garage

Quote:

Originally Posted by Tim Hancock

.... after figuring out FOR SURE which is the low side fitting...

This is the part I'm concerned about for obvious reasons. The generic instructions they give you on these hose and valve kits is the reason I have not bought one. Any way to know FOR SURE?

vonsmog · 06-12-2008, 05:22 PM

Steve,
My Jeep Grand Cherokee gets two cans every spring, as I have a slow leak. I just use the hose and valve kit that you can buy. It will last all summer and die out when winter comes. Sure beats spending over $1k to fix it right. Two cans of 134A cost only $13 bucks a year!
Von

Tim Hancock · 06-12-2008, 05:39 PM

Quote:

Originally Posted by Dan in Pasadena

This is the part I'm concerned about for obvious reasons. The generic instructions they give you on these hose and valve kits is the reason I have not bought one. Any way to know FOR SURE?

On most vehicles that came with 134, the charge fitting will only go on the low side. If you have a manual, it will tell you, but you can also figure it out by following hoses. High side is from compressor to condensor (in grill on most cars) to drier to expansion valve. Low side is after evaporator (buried in car dash) before returning to compressor. A quick google search will probably turn up a basic auto AC diagram showing the basic components of auto AC systems I mentioned above.

masraum · 06-12-2008, 06:09 PM

Thanks all.

mattdavis11 · 06:19 PM

If you can screw up connecting the low side fitting on a retro'ed 134 car, you shouldn't be messing with the system.

The low side has a fat hose/line, the high side hose/line is thin. The hose may be the same size, but the metal line will not. The big fitting for 134 is high, small is low. Always charge on the low side. The cheapo guage at the local parts store won't sell you the wrong size.

For 134 in Texas on a Porsche (works on a 944) try 82.5 to 83% of the recommended charge for R12. Ymmv because you won't be vacuuming the system down, and repairing leaks, long lines from the back, yada, yada....

Let me know if I can help. Ditto what Tim had to say. A fan to keep the condenser cooler in this heat will most definately help.

wrecktech · 06-12-2008, 07:51 PM

Tim's explaination is right on. I have done this probably 50 times the only thing different is we use an evacuator first. You can buy a 3 can kit with the hose for about $35 and a can of mild stop leak for about $10. Your problem is most likely that the seals are going bad. Read the instructions and it is pretty foolproof.