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Vacuum and the auto A/C
Q: How do I vacuum the Auto A/C System?
A: In order to vacuum the auto A/C system, you need a standard manifold gauge set and vacuum pump. Start by being sure that all control valves on the gauge set are closed. With the pressure gauges connected to the A/C system (red hose to high pressure side and blue hose to the low pressure side) connect the yellow (center hose) to the vacuum pump. Start the vacuum pump and then open both high and low side control valves on the manifold gauge set. This assures that vacuum is being pulled throughout the A/C system.

Typically vacuum is pulled for about 1/2 hour, but that will depend on the condition of the system and the work being performed. In the case of regular maintenance, a 1/2 hour vacuum at 29.9" should be fine. Where a system has been contaminated or suffered catastrophic failure (ie.: seized compressor) it's generally a good idea to vacuum for at least 1 hour or more to assure a totally dry system.

It's also important to assure that your vacuum pump pulls deep vacuum. Water does not boil until the level of vacuum is under 1,500 microns. Deep vacuum is considered to be under 750 microns. Ideally, for automotive service, you should attain at least 200-300 micron vacuum if not lower. If you're using a typical rotary vane vacuum pump, you will also want to see this information vacuum pumps in our 'fast track' section about using vacuum pumps for auto A/C service. If you own a rotary vane vacuum pump, you really need to see this information about What Vacuum Pump Manufacturers Really Don't Want You to Know.


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Our list of FAQ's is growing, so please visit back often. If you can't find the right answer here, visit the auto A/C help and discussion board at the COOL ZONE. You'll get all the right answers to your questions about troubleshooting and diagnosing auto A/C systems.

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