Leak detection is essential to HVAC system maintenance, but low-pressure refrigeration systems operate differently from their high-pressure counterparts — and require a specialized approach.
So, how charged low-pressure refrigeration machines may be most efficiently leak checked?
In this post, we’ll walk you through the most efficient and EPA-compliant method, show you what to avoid, and provide tools and tips to ensure accurate leak detection.
Why Leak Detection Is Unique in Low-Pressure Systems
Low-pressure systems that use refrigerants like R-123, R-11, or R-113 typically operate under a vacuum. This makes them prone to a different kind of problem:
Instead of refrigerant leaking out, air and moisture can leak in — which contaminates the system and reduces performance.
This also means standard leak detection tools and methods don’t work effectively while the system is still charged. That’s where a specialized approach is needed — one recommended by both the EPA and ASHRAE.
The Most Efficient Leak Check Method for Charged Systems
Charged low-pressure refrigeration machines may be most efficiently leak checked by raising system pressure through controlled heating.
Here’s a step-by-step guide:
Raise Pressure by Heating
- Apply electric heating blankets or warm water to the evaporator or chiller barrel.
- This causes the refrigerant to expand, which raises system pressure above atmospheric levels.
- Once pressure is positive, any existing leaks will cause refrigerant to leak outward, making them detectable.
Recommended Tools for Leak Detection
Once system pressure is raised:
- Electronic Leak Detectors – Halogen or ultrasonic tools can precisely locate leaks.
- Soap Bubble Solution – Apply to joints, fittings, and flanges to visually detect bubbles.
- Vacuum Gauges – Monitor pressure to ensure it remains in a safe range before and after testing.
What Not to Do: Adding Nitrogen to a Charged System
A common misconception is to use dry nitrogen to pressurize the system while it’s still charged. This is not safe and not legal under EPA regulations.
Never add nitrogen to a charged refrigeration system.
Only use nitrogen for leak checking after refrigerant has been recovered.
Why this matters:
- Mixing nitrogen with refrigerant can be dangerous and lead to combustible conditions
- It contaminates the refrigerant, complicating recovery and reuse
- It’s a violation of EPA Section 608 regulations
Pro Tip: If you’re working with an R-123 chiller, reducing refrigerant loss from the purge unit is another critical step.
Check out our expert guide on reducing refrigerant loss from a purge unit to avoid unnecessary emissions and improve system efficiency.
FAQ: Leak Checking Low-Pressure Systems
How do you leak check a charged low-pressure refrigeration machine?
By raising system pressure using heat, which allows refrigerant to escape at leak points and be detected with soap bubbles or electronic tools.
Can you use nitrogen in a charged system?
No. Dry nitrogen should only be used after the refrigerant has been fully recovered.
What refrigerants are used in low-pressure systems?
Common refrigerants include R-11, R-123, and R-113.
Why don’t standard leak methods work on low-pressure systems?
Because these systems run under vacuum, air leaks in rather than refrigerant leaking out — making traditional methods ineffective.
Want to go deeper? Understanding your chiller’s normal charge is key when calculating leak rates after detection.
Here’s the best method to determine a chiller’s normal charge for leak rate calculations
Final Thought
Leak detection on low-pressure systems doesn’t have to be tricky — as long as you know the right method. With this guide, you’re ready to handle it safely, efficiently, and in full compliance.
Want more HVAC tips or EPA 608 prep help?
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