What can be used to pressurize a chiller system before opening it for a non-major repair?

The appropriate method for pressurizing a chiller system before performing non-major repairs is by using dry nitrogen. This is because dry nitrogen is inert and does not react with other materials, making it ideal for pressurizing systems without the risk of causing any chemical reactions or contamination within the refrigerant lines. Additionally, dry nitrogen can help to detect leaks if any occur during the repair process, as any drop in pressure can indicate a problem.

Using an air compressor or refrigerant gas can introduce moisture or contaminants into the system, which can lead to corrosion or other systemic issues. Controlled hot water, while potentially useful in some contexts, is not typically suitable for pressurizing a chiller system as it may not exert the necessary uniform pressure needed for proper diagnostics and can also introduce other complications.

Thus, dry nitrogen is the correct choice for safely and effectively pressurizing the chiller system prior to opening it for maintenance.