If the system is low on refrigerant, there is a low pressure switch which shuts the compressor off to prevent damage. The refrigerant circulates refrigeration oil with it to lubricate the compressor; if the refrigerant charge drops too low, it is designed to shut off to prevent compressor damage from lack of lubrication.
If your Honda has a refrigerant leak, there are 2 different methods that a technician uses to locate such leaks for repair. He will need to put some refrigerant in the system, in order to make the compressor run, so that he can detect where it is leaking out.
(1) By using an electronic leak detector. The electronic detector makes a steady beeping sound; when the probe of teh detector is passed near a leak and comes in contact with refrigerant gas, the sound of the beeping will increase in frequency, much the same as a metal detector does. By pasising the probe back and forth, you can zero in on small leaks this way. THis method is not used as much as it once was, but is useful for locating leaks in hard to reach places such as up inside evaporator cases.
(2) The standard method of leak detection now is UV dye testing. The technician adds a small (1/4 ounce) amount of a liquid dye to the refrigeration oil in the system, and allows the AC to fun for a few minutes. THen, by inspecting the components with a high intensity UV lamp, he will look for traces of dye seeping out with any small refrigerant leaks; the dye will fluoresce bright green/ yellow under teh UV light although it is practically invisible in ordinary light. This type of leak detection works especially well at locating small seepage type leaks that take several days to leak any appreciable amount of refrigerant. Many vehicle manufacturers are now adding this dye at the factory, because it works so well.
At the age of your car, it would not be unusual to have a couple small leaks, due to degradation of the rubber o-rings, seals, and hoses in the system.
One other note: This system is designed to operate on R-12 refrigerant. Do not let anyone attempt to "convert" it to use R134a, as from that point onward it is likely to leak much more rapidly and need constant periodic recharges to keep it operating. Converting a system correctly is much more expensive than using R12 to recharge it. R134a molecules are much smaller than R12 ones, and tend to leak through the walls of the rubber AC hoses used in R12 systems; even more so when the hoses are old and degraded.. Systems designed to operate on R134a use a special barrier type hose material, with a plastic liner.
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