Ok.. one last comment here... based on a conversation I had with some buddies today. We were talking about this thread and about Ben's post in particular. Someone said to me "You aren't going to stop those who want to invest $30 bucks in a kit from doing so. They don't have working air to start with, if it works for a while great, if it trashes their system, they are not any worse off." And then ," You'd do better by telling them when and how to use those kits."
I gave it a lot of thought today, and I suppose there is some truth in what he said. So, with the initial warning that I do not endorse nor recommend these $30-$40 reftorfit kits, and in the vast majority of cases think you do more harm than good.... let me try and see if I can come up with some recommendations.
First. When is a kit NOT appropriate. Hmm, if you have a crumped compressor, do not replace just the compressor and add a kit. Usually a bad compressor will have contaminated a system beyond your imagination in its death throes. The only sure fix is to flush and replace whatever cannot be successfully flushed. Oh and if you EVER have a system open, always replace the receiver/dryer (or accumulator depending of the manufacturer and type of car - same thing more or less for our purposes). Another - you have a 93 and earlier system (or some 94's were also R-12). The cooling is there but low. DO NOT JUST ADD A KIT. (see below). I am sure there are other times a kit may not be appropriate, but that all I can think of at this instant. (bearing in mind I do not think a kit is EVER a really good idea)
NEXT... When might we try a kit. Ok... You have an otherwise semingly good system that gradually over time seems to blow warmer and warmer air until it stopped blowing cool air altogether. We can assume there is a slow leak and you lost your charge of R-12, or most of it.
Here's the rub here. R-134 molecules are significantly smaller than R-12. If you had an R-12 leak, imagine the leak rate with R-134. Can you fix leaks? sometimes. And sometimes the leak fixer stuff in cans might work (see Ben's post). Two most common leak areas ? Compressor seal (fixable but not for 99% of DIY'ers) or valve cores. The valve cores in an R-12 stem look like big bicycle tire schraders - and in fact they more or less are. Screw right in and out in the same fashion. A definite DIY job to replace these ASSUMING THERE IS NO REFRIGERANT CHARGE. Bad news about refrigerant (some call it freon, but that is a DuPont trade name so I try and call it refrigerant) if some squirts you in the eye, you WILL lose the cornea or sight in that eye. Goggles or suitable eye protection are a must while working on a system with any charge in it. "Well" you ask "How do I know if I have a charge? Can I hook up a simple gauge from the $40 kit and see ? Yes and no. The AC will not operate if the charge falls to a certain level. If the AC is not operating, and there is enough freon to saturate the system (not a lot needed for this) the pressure will be the same in a non operating low charged system as it would be with a full charge. Put another way if you put 6 oz of refrigerant in a closed 5 gallon container it would read the saturated pressure of the refrigerant(pretty close in PSI to degrees farenheit at normal temps, eg. 70 PSI at 70 degrees). If you filled it 3/4's full, it would read the same. So reading a partially charged system in a static or non operating state won't help you determine anything. If the charge is so low you cannot run the system, you KNOW you are really low, just not HOW low. NOW folks, understand venting R-12 into the atmosphere is against the law. The fine is extremely high. But I have seen some folks will try a little test, figuring a little vented to fix a system is better than refilling one and letting the entire charge bleed away. What these folks do is to use a little stick or small screwdriver and press down on the schrader valve for about 5 seconds and see if the hissing stays the same or starts to lessen- these same folks ALWAYS have eye protection when I have seen this. IF i the hissing stays the same there is probably a decent amount of refrigerant in the system. If is falls off, they stay with it and bled off what in all probability was a VERY slight remaining charge, until it is gone.
If the charge is a decent one (good steady hiss), it should be recovered by someone with the equipment o do this. I'll offer no other ideas or suggestions, PERIOD. Mind you I am not suggesting the former either, just telling you what I have seen in my long life.
So with your charge gone, either my leaking away to by being recovered, next what? Ok here is where I differ greatly with the kit idea. You spent $30-$40 on a kit. Have access to an air compressor? Buy one of those $15 Harbor Freight venturi air pumps. Buy a single r-12 hose with a shut off on one end. (another $15). Connect this to the valve on the high pressure side. .This is the smaller line running from the compressor to the condensor in front of the radiator - or maybe just after the condensor running back to the receiver/dryer again, it varies, the line will be the smaller, usually metal, ) Hook the other end to this venturi pump and hook up an air compressor. Run this as long as your compressor can stand it... 30 mins should be good. (relatively speaking). Add the changeover fitting to the other valve (the one on the bigger hose leading from the firewall of the car to the compressor or maybe on the receiver dryer AFTER the expansion valve - it varies. If it is on a line, the line will be the bigger of the two. ) do this while the vacuum pump is running). When you have run the pump as long as you can or at least 30 mins if able close the valve on the hose and shut off the pump (shut off the air compressor in other words) connect the 1st can up from the kit and let it run into the low side UPSIDE DOWN. (I know I said NEVER, but the kit ONLY has a low pressure fitting, and if the system is not running this is safe. NEVER DO THIS ON AN OPERATING SYSTEM, EVER EVER EVER!!) It should take the entire can. Let it sit a few minutes to equalize in the system - eg. vaporize past the expansion valve until the pressure is equal on both the high and low sides of the system. Quickly unscrew the hose from the high side fitting. There should be adequate system pressure there now to keep air from leaking in, in fact some refrigerant may leak out as you unscrew it, that's ok.
Next, start the car and see if the AC will operate on this level of charge. If it does, the rest of the rerigerant goes in on the low pressure side, can RIGHT SIDE UP. A can or pan of hot water to float the can in as the refrigerants is fed into the system helps speed the process. More or less follow the kit directions at this point.
That's the best advice I can give. I don't believe in the kits. I do not recommend them, but if you absolutely have to use one, maybe this will help.
Happy Exploring
Chris