DLS A2L Dissipation Sequence

Change is inevitable. Gone are the days of good ol’ R22 and T87 thermostats. Give me an A-min (area minimum) if you know what I’m talking about! And now, because R410 has a high GWP (global warming potential), the industry has shifted to A2L refrigerants. With the change comes all these new acronyms, like Mrel (total releasable charge), Hinst (height of installation above floor), and… 

LFL (Lower Flammability Limit): 

• Minimum concentration of combustible gas or vapor in the air that cannot ignite 

• Defined as a baseline threshold for detection for R454B leak detection sensors 

• The LFL for Puron Advance™ is 11.8% 

Because of LFL, we must have some form of dissipation. Dilution is the solution! This is the dissipation sequence of operation for Carrier Bryant DLS or Crossover systems. 

More acronyms to know: IDU (indoor unit), ODU (outdoor unit), MZU (multi-zone unit). 

One to One Systems (Crossover included) 

When a leak is detected above the LFL threshold: 

• Error code EH C1 is displayed on the IDU 

• A continuous audible alarm emits from IDU (persistent beep) 

• IDU fan shifts to turbo mode; louvers fully open 

• ODU shuts down 

When the leak drops below the LFL threshold: 

• Audible alarm resets after approximately 2 minutes 

• Error code clears after approximately 5 minutes 

Tech Tip: The audible alarm can be turned off by pressing the power button on the wireless remote/wired controller, or the forced operation button on the air handler interface board (but it will not clear the error code or take it out of dissipation). 

Multi-Zone Systems 

When a leak is detected: 

• Error code EH C1 is displayed on the IDU detecting a leak 

• Continuous audible alarm emits from the IDU detecting a leak 

• All other IDUs not detecting a leak will display EC C1 

• All IDU fans shift to Turbo fan speed; louvers fully open 

• MZU shifts to AC and closes all EEVs (electronic expansion valves)  

• Then the system pumps down for approximately 40 seconds 

• EBV (electronic ball valve) in MZU closes 

When the leak drops below LFL threshold: 

• Audible alarm resets after approximately 2 minutes 

• Error codes clear after approximately 5 minutes 

• Valves and MZU resume operation after approximately 2.5 hours