What should you never do when a system is in deep vacuum?

When a system is in deep vacuum, it is essential to avoid energizing the compressor because doing so can cause it to operate without sufficient refrigerant. In a deep vacuum, there is little to no refrigerant in the system, which serves as a lubricant and a cooling medium. Running the compressor under these conditions can lead to severe damage, such as overheating, scoring, and eventually, compressor failure due to lack of lubrication.

In HVAC systems, compressors are designed to compress refrigerant gas; if there is no gas to compress, the internal components may rapidly wear down or become damaged. Therefore, ensuring that the system has appropriate refrigerant levels before starting the compressor is crucial for the longevity and performance of the equipment.

Using a micron gauge, which measures the vacuum level, is appropriate and necessary during the evacuation process, and adding refrigerant is also essential once the system is ready. However, energizing the system fans and blowers may be acceptable in some cases as long as the system is not attempting to operate in a compressor-driven capacity without proper refrigerant levels.