Arrived on site to check out the unit that does the right side of the new addition for no cooling, upon our arrival yesterday the unit was frozen solid. We turned it off to allow it to defrost, we removed the air filters and started up the system. Although the filters were dirty and my initial reaction was it was freezing up because of the filters, it turns out that the system was low on refrigerant which was causing the unit to freeze up. We topped off the refrigerant charge and will need to return to perform a leak test on the unit, I reinstalled the old filter and confirmed that it did not have any effect on the operation of the system.