This has always been a pet peeve of mine- AC work is not difficult at all, but there are a few "gotchas."

First you will need a manifold/gauge set. Do not buy a can of refrigerant with a gauge on it and think you can recharge your system. You cannot. Harbor Freight has the cheapest "good" set I have found yet:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=2435

Most of the ones you get at auto parts stores are crap and will fall apart after a few uses (and are more expensive). Beware when you buy a set that you will need hoses and quick-disconnect fittings to attach them to your car (many do not come with them and SURPRISE they are not cheap!).

Also note that R134 (~93 and newer) and R12 (~92 and older) hose ends/fittings are not the same. The manifold sets can be interchanged but good luck finding older hoses.

The first thing to do if you are just checking or needing to add some refrigerant to a system is to assemble the gauges and make sure all the fittings are tight. Make sure that the valves are closed (should be all the way clockwise).

Attach the high side hose (red) to the high side service port and the low side hose (blue) to the low side service port. On R134 systems you can't get this wrong- the hoses/gauges should be color coded and the fittings can't be interchanged. I think there was more variance on R12 systems depending on mfr. R134 systems use the snap-type quick disconnects; most are preloaded and snap on, and you pull up on the collar to release. Some you have to pull the collar up on to get them to snap on. Either way, snap the fittings on with the AC off and make sure they are snug. If you can identify a leak by sight or sound then somthing is wrong- get the fitting off immediately to avoid discharging the system any more than you have to.

With the gauges connected and the AC off the gauges should have the same reading which in psi should be approximately the ambient temperature in degrees F or a little higher. More than maybe 10psi over that and the system is probably overcharged. Less than that and it is undercharged. Go ahead and start the engine and AC and let the system stabilize for a few minutes. Pressures and performance are generally weaker at idle and will come up some with RPMs. Go ahead and rev the engine some (I would recommend around 2000 or 2500 RPM) and see where the system stabilizes.

For R134 systems this should be between 250 and 300 psi on the high side and <45psi on the low side. Anything in that region and you should probably not mess with the system.

For R12 systems the high side reading should be between 200 and 250psi. Anything in that region and don't mess with it. Do not try to over charge it.

R134 systems start cooling around 150psi on the high side. R12 systems will start cooling around 100psi on the high side. If your system cools, but not great, this is probably why- a slow leak has dropped the charge and you need to add some.

To add refrigerant, get a can and a can tap valve. Make sure the valve is fully open (counter-clockwise) and the pin is all the way retracted. Screw the valve onto the can, then screw in the handle all the way to pierce the can. The can is now pierced with the can closed. Obviously, don't remove the valve until the can is empty, otherwise you will discharge the open can.

The tap valve connects to the center hose (yellow). Connect it, snug, then open the valve on the can. Most manifolds have a valve above the port to purge any air in the line- depress it for a second to clear the air out of the line. If you don't have a purge valve you can unscrew the hose slightly to purge the air, then retighten. The idea is that you get the air out of the system. The air contains moisture, and moisture will combine with the refrigerant to form HCL which will obviously start ruining things quick (this is why the AC system has a drier, but it's good to just keep moisture out from the start).

With engine runnig and the AC on and the tap valve on the can open, open the low side valve on the manifold to allow the system to start charging. ALWAYS CHARGE WITH THE CAN IN THE UPRIGHT POSITION. NEVER CHARGE WITH THE CAN ON ITS SIDE OR UPSIDE DOWN. Continue revving the motor slightly to keep the AC off idle (where it works). Watch the high side gauge as it should start to rise. For most R134 Hondas you will want to charge to around 280psi on the high side. Shut the low side valve when you reach the proper charge, then close the can tap. You should be able to see the level in the can drop as frost condenses on the outside of the can.

At this point you should be done.

If your AC turns on and is charged but doesn't work that great, make sure the condensor and radiator fans are both working. You need that airflow for the AC to really work. If your AC compressor doesn't turn on at all, you might have too low of a charge (bad leak) or have an electrical issue.

Please note the instructions above will NOT work for you if your system is empty. You will need to ID the leak and then flush the system (not the compressor), repair the leak, replace the drier, then vacuum down and recharge the system. Not doing so will generally destroy and good compronents in the system if you just recharge and leave you with more trouble than you started with.

 

^^faq material for sure. i'll keep this in mind for the future.

 

Does this improve/rid the bogging the ac causes when idling, etc?

 

No- those are fuel/ignition issues that are a combination of other things. If your car bogs with the AC on, I would make sure that your ignition system is tip-top and you don't have other issues, like a crap O2 sensor or clogged cat.

 

This is great info! Thanks, Todd! I will definitely print this out and have it alongside me when I recharge my system at the weekend.

 

Watch the high side gauge as it should start to rise. For most R134 Hondas you will want to charge to around 280psi on the high side.

Does this figure of 280 psi depend on the ambient temperature at all? Is it a good rule of thumb for any weather, or should it be modified in particularly warm or particularly cool temperatures?

 

It all depends on ambient temp, but should not vary more than, say, +/- 20 psi. I would suggest 280psi @90F ambient and add/subtract pressure=degrees F from there.