Air Power Vacuum Pumps
There are two kinds of vacuum pumps generally available. The cheaper of the two is the air power, or venturi type, pump (see illustration). The venturi type pump is easy to use and maintenance free. It has no moving parts and requires no lubricating 011. What’s the catch? Well, it requires a compressor that can pump at least 80 or 90 psi. And a compressor that pumps 80 to 90 psi for half an hour is using a lot of electricity.
How do you use this type of vacuum pump? Follow these steps:
1 Before using a venturi type pump, always discharge the refrigerant first.
2 Connect the manifold gauge set center service hose to the vacuum pump inlet labeled VACUUM.
3 Open the high and low side manifold gauge hand valves as far as possible.
4 Connect an air hose to the vacuum pump inlet labeled AIR INPUT or
5 Note the reading indicated by the low side gauge and begin timing the evacuation when the gauge indicates a vacuum reading. Note: If, after a couple of minutes, no vacuum is indicated on the low side gauge, inspect the system for leaks and repair it before proceeding. Check the gauge set hose connections first.
6 After about five minutes of pumping, the required vacuum reading (which, remember, varies with altitude) should be indicated on the low side gauge. When this reading is obtained, close both the gauge valves and then disconnect the air hose. Note: If the required vacuum reading is not obtained within 10 minutes, inspect the gauge set hose connections, the hand valves and the system fittings for leaks. After correcting the problem, repeat Steps 1 through 5 and continue the evacuation process.
7 Allow several minutes for the system to stabilize and check the low side gauge to determine whether the system is maintaining vacuum.
a) If the system is holding vacuum, reconnect the air hose, open both hand valves and continue pumping for at least 30 minutes to complete the evacuation process.
b) If the system is losing vacuum, check to make sure the leak is not at the gauge set connections. If the leak is not at the connections, charge the system, use a leak detector to locate the source of the leak, discharge the system, repair the leak and repeat the evacuation process.
8 When the evacuation process is complete, close the gauge valves and disconnect the air hose.
9 Check the low side gauge to make sure the system maintains vacuum.
10 Disconnect the air pump at the center hose.
11 Recharge the system.