I have a Rheem condenser (model 13AJN) and air handler. The condenser sits on the roof of the building and the air handler sits above the dropped ceiling inside the building. The building is 6 stories and my suite is on the 5th floor. My Rheem unit was installed in the spring on 2012. (I had a Carrier unit before the Rheem was installed.) Whenever the outside ambient air temperature drops to around 38 degrees or less the condenser will freeze up. Luckily I'm in Houston, TX so this doesn't happen for long periods or very often but it does happen. My AC contractor put a pressure switch (Johnson Controls) on the condenser to cycle the fan off about six weeks ago but it the unit is still freezing. My AC guy is now saying that he is going to install a low ambient kit, supplied by Rheem. It sounds to me like the low ambient kit will do the same thing as the pressure switch that has already been installed. Are these two things the same? The rooms being supplied by this AC unit need to be fairly cool all year round (about 72 degrees). Now, my AC guy is saying that maintaining 72 degrees, even in the winter, is not possible. My old Carrier was able to accomplish this for 10 years. The only difference between the old and new units are the manufacturer and the refrigerant. The Carrier used R-22 and the Rheem uses R410. Could the type of refrigerant be the cause of the freezing?