Originally Posted by Ladywendolyn
I called the dealer and they told me that it was related to high heat and humidity issues. (Isn't that what an air conditioner is for?)
They told me that after a day of running on high, sometimes there is ice buildup which would normally melt at night.. but I was running it so much that it didn't melt.
First, I would stay away from that dealer for future service work. I never cease to be amazed at what some dealers will tell their customers especially about air conditioners.
That is exactly what air conditioning does, it removes heat from a space and it dehumidifies the air.
Two things cause a unit to ice. One is low freon, which is not that common because these units are charged at the factory through what is called a process stub. The charge is measured in so it is exact, then the stub is crimped, cut and welded so that it cannot leak. These units are completely sealed. I have only seen two with leaks and those were caused by a section of the copper tubing rubbing against another metal part and abrading a small hole in the copper. These ACs only use around 1 lb of refrigerant, so to have any freon at all left after suffering a leak is highly unusual, making "low" charge unlikely. It's possible for one t leave the factory undercharged, it does happen occasionally, but if that's the case, the unit will not operate correctly from the start. The most common cause is air restriction. This is caused by too small or improperly installed ductwork, or dirty filters, anything that would reduce the volume of air flow through the evaporator. Also, these rooftop air units are very sensitive to air flow, and in some cases, even closing off one vent can restrict it to the point of icing up.
Given proper air flow, running the unit all day will not cause it to ice. Air conditioners work on the principle of a 20 degree split across the evaporator. That would be the difference between the return air(room air) and that air that comes out of the grill. If the trailer is 75 degrees, the discharge air should be around 55 degrees. As the room temperature drops, so does the evaporator temp. Icing occurs when the evaporator temperature goes lower than 32 degrees. The condensate then starts freezing on the coil, the more it condenses the more accumulation, and eventually the ice will block off the air flow. In order to ice because of running an extended period of time, the inside of the room would have to reach 52 degrees in order to get the evaporator below freezing, based on a 20 degree split, and the probablility of that happening is pretty low.
If you are already having an icing issue, running the unit at a lower speed will only aggravate that. If you run the blower slower, you are ruducing the amount of air over the coil, thereby creating an artificial air flow restiction. Remember, you want more air going through the coil, not less.
Low charge.. There is a way to diagnose that by measuring current draw to the compressor. It should draw a given amount of current based on the ambient temperature of the outside air, not the air inside the trailer. The manufacturer's data plate gives the amp draw of the compressor. That number is based on 95 degree ambient temperature. It will draw more if it's hotter, less if it's cooler. Unfortunately most RVers do not own an Ampmeter or know how to do this. Equally unfortunate is that most RV service techs don't know how to do it either. That accounts for all of the crazy stuff we read on the forums about what a dealer said as well as the number of air conditioners needlessly sold to unknowing customers.
Seann, I would be interested to know how he diagnosed your "low charge" problem. If he didn't use the current measuring method, he would have to have used a piercing valve to attach his gauges, and then whether it was low on charge or not, he would have then had to dump the charge, fix the hole from the valve, sweat in a shraeder valve(service port) and recharge the unit.
I apologize for this being such a long winded post, but hot weather is around the corner, and the posts about poor cooling are going to start appearing. Hopefully some of this information will arm you with a little knowledge, and keep you from being ripped off.
One more thing that I forgot that will also cause a unit to ice up. If the plenum(blower area) isn't taped correctly, the blower can circulate air right back to the evaporator coil and rapidly lower the temperature of the coil. Once that happens, you start getting ice.
So... If your unit does not cool properly, before you haul your trailer to a repair shop where you most likely be ripped off..
1. Clean the filter
2. Open all of the discharge vents
3. Check for improper taping in the blower area
4, Make sure your fan is set on high.
BTW, running the fan on a lower speed does not change the speed of the compressor. That is going to be constant.