If it cools properly at times, low charge is most likely not the issue. The next time it quits, check right away underneath to see if water is dripping next to the right front tire. If it is not, the evaporator is getting too cold and the condensation is freezing and blocking air flow. I suspect that isn't the cause of the problem because it wouldn't melt and start working again until the system was turned off for quite a while.
Another common cause is moisture in the system. That happens when it is opened to replace a part, then it isn't evacuated for a half hour before recharging with refrigerant. When air gets in the lines, humidity is in it too. That moisture will freeze when it goes through the metering valve. That stops the flow of refrigerant, but the ice will melt on its own fairly quickly. At that point the cooling will take place again until the next time that droplet of water circulates around.
The orifice tube could be hanging up too. That is more likely to occur with a new one than with one that's been working fine for a few years.
There's no way to tell if the system is low on charge except to recover what's in it now, then charge it with a measured amount. The do-it-yourself cans rarely have the exact amount of refrigerant needed to install the correct charge. Unlike home refrigerators, automotive systems can handle a little over-charge, but too much can allow liquid to slosh into the compressor and lock it up.
If you do try to add to the system, be aware that refrigerant can cause blindness and frostbite. Professionals wear gloves, safety glasses, and a face shield. The cans charge through the low side port which will be on the hose between the firewall and compressor.
Thursday, July 10th, 2014 AT 11:48 AM