Inches of vacuum  on low side gauge (inches Hg) Temperature at which water boils (°F) Absolute pressure (psi)  0  4.92  9.23  15.94  20.72  24.04  26.28  27.75  28.67  28.92  29.02  29.12  29.22  29.32  29.42  29.52  29.62  29.74  29.82  29.87  29.91  212  204.98  194  176  158  140  122  104 86 80.06 75.92 71.96 69.08 64.04 59 53.06 44.96 32 21.02 6.08  –23.98  14.696  12.279  10.152 6.866 4.519 2.888 1.788 1.066 0.614 0.491 0.442 0.393 0.344 0.295 0.246 0.196 0.147 0.088 0.0049 0.00245 0.00049 16-55 Figure 16-91.  A vacuum pump is used to lower the pressure in the  vapor cycle air conditioning system. This reduces the boiling point of  water in the system, which vaporizes and is drawn out by the pump. Figure 16-90.  When the temperature is low, a greater amount of  vacuum is needed to boil off and remove any water in the vapor  cycle system. Figure 16-89.  A 30 pound R134a refrigerant container with dual  fittings. The fitting controlled by the blue valve wheel opens to the  vapor space above the liquid refrigerant for connection to the low  side of the vapor cycle system. The fitting controlled by the red  valve wheel draws liquid refrigerant from the bottom of the cylinder  through a stand tube. This fitting is connected to the system high  side. On containers without dual fittings, the container must be  inverted to deliver liquid refrigerant through a connected hose.  System Servicing devices used to find leaks. There are many types available  that are able to detect extremely small amounts of escaped  refrigerant. The detector is held close to component and hose  connections where most leaks occur. Audible and visual  alarms signal the presence of refrigerant. A detector specified  for the type of refrigerant in the system should be chosen.  A good leak detector is sensitive enough to detect leaks that  would result in less than  1 ⁄ 2 ounce of refrigerant to be lost per  year.  [Figure 16-92] Other leak detection methods exist. A soapy solution can  also be applied to fittings and inspected for the formation  of bubbles indicating a leak. Special leak detection dyes  compatible for use with refrigerant can be injected into the  vapor cycle system and can be seen when they are forced  out at a leak. Many of these are made to be visible under UV  light. Occasionally, a leak can be detected upon close visual  inspection. Oil in the system can be forced out of a leak,  leaving a visible residue that is usually on the bottom side of a  leaky fitting. Old hoses may become slightly porous and leak  a significant amount of refrigerant over time. Because of the  length and area through which the refrigerant is lost, this type  of leak may be difficult to detect, even with leak detecting  methods. Visibly deteriorated hoses should be replaced. Vapor cycle air conditioning systems can give many hours of  reliable, maintenance-free service. Periodic visual inspections,  tests, and refrigerant level and oil level checks may be all  that is required for some time. Follow the manufacturer’s  instructions for inspection criteria and intervals. 