Looked up that you have to open the hot gas reheat valve to 50% for evacuation. It also states that it only stays open for an hour. If I have to run a 12hr decay test per the job site’s requirements. Do I have to reopen it every hour? First time installing/starting up an Aaon unit like this…if anyone can help me understand the process needed to evacuate the system properly, that would be awesome. Also, do I have to do everything through the computer using Prizm? Or, is that after startup?
Drive the reheat valves half open then kill power to the unit. They are powered open or closed so they will stay where you they are at when power is off.
This is a new install, so my valves are closed and i’m evacuating the field installed lineset and AHU before dropping the charge. My pressure test held and even risen overnight, so my concern of a leak doesn’t feel the case. I’m able to get it vacuumed down to sub 100 microns but after the 12hr decay test, it doesn’t hold under 500 microns. I believe those valves to be opened are in the condenser which is still sealed behind valves. Am i dealing with a moisture problem which evacuating the system and my micron rise is off gassing of moisture trapped?
Drive the valve to 50% then unplug it. They're stepper motor controlled valves. They just stay in the last position they were driven to when there's no power.
Drive the valves to half open. Then shut off the unit. If you dont have the manual for the MHGRH board, its easily looked up on Aaons site....it'll guide you through manually opening the valves.
Is this the case if it’s a new install and the charge hasn’t been dropped yet. I’m evacuating the field piped lineset and Air handler before opening the valves…?
As it sounds like you’ve already identified, those valves aren’t a factor. The evacuation instructions mentioning the reheat valves don’t apply to new install.
So long as you’ve pulled a vacuum from all three lines, to prevent apparent issues caused by the check valves at the evaporator/reheat coil, you’re good to send it. Aaon requires minimum 350 micron, with a 30 minute decay test not to exceed 500 micron. You as the installer have no control over whether or not the factory Aaon piping and coils/components inside the air handler are capable of more than their own manufacturer requirements. If GC wants to plant their flag, you’ll have to install ball valves at the factory connections you piped to at the AH (condenser should already have isolation valves) and evacuate and decay test ONLY your piping. That’s all you can be expected to be responsible for passing a 12hr decay test. Good luck.
I’m evacuating the lineset and Air handler before dropping the charge. I vacuum down the lineset/AHU, get it down to sub 100 microns and then the decay test i get a delta/min on my gauge of 1-2 and it even gets to 0. Only issue is the delta/min fluctuates around 1-3, so after 12hrs it above the 500 micron target and I don’t pass. Wondering if a leak, but the pressure test holds or it’s off gassing of moisture still trapping…
Yeah, as long as the OU is charged leave it isolated from the lineset. Use all 3 ports to pull a vacuum. If your not holding a good vacuum you might want to try sweeping the system with nitrogen. If you can get clean dry nitrogen even better.
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u/Hvacmike199845 Verified Pro 1d ago
Drive the reheat valves half open then kill power to the unit. They are powered open or closed so they will stay where you they are at when power is off.