Roof Mounted Rheem Condenser Freezing Up

[gonzo715]

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?

[BaldLoonie]

With proper low ambient kit, I don't see why you can't keep the room 72°. That ain't very cold by A/C standards. Unless he had the fan cycle kit set too low, used to the 22 days. Or could have a bad expansion valve causing the freeze ups.

[Hunter844]

1. You need a low ambient in order to run cooling in cold conditions. I would think that would have been done right outright. There are other switches that can be installed at the evaporator that essentially do the same thing.

2. So he didn't replace the indoor A/H section with a matching A/H to the outdoor section? Did he do any sort of conversion of the coil to R410a?

3. I would think the unit should be capable of maintaining 72 degrees even with a mismatched system but there is too much information lacking to really make big bold declarative statements.

[gonzo715]

The Rheem unit is matched. Both the condenser and air handler were replaced at the same time, same manufacturer. I really appreciate any help with this.