PriklyPete Report post Posted September 2, 2013 My friend has a roof air conditioner that is frosting up at the outlet where it enters his coach - what can cause this and should he be worried about it? Share this post Link to post Share on other sites
wolfe10 Report post Posted September 2, 2013 PriklyPete, Welcome to the FMCA Forum. Formation of frost is generally a sign that air flow through the evaporator is restricted. So, in order: Check air filter(s). Clean or replace as needed. Fan speed on high. If a thermostat, consider a warmer setting along with higher fan speed. If this doesn't solve it, particularly if this is an older unit or has been operated a lot in humid climates, he will need to clean the EVAPORATOR. The air filters on RV A/C's are not that effective. The combination of dirt in the air and wet evaporator coils deposits a lot of dirt. This is only serviceable from the roof. Use a commercially available evaporator cleaner from any box store. Be sure to put a towel or otherwise block off the duct into the coach when doing this. You would be AMAZED at how much dirt can accumulate on the fins, restricting air flow. It is also the cause of that "wet dog" smell when first turning on an A/C. You are literally smelling the mold that grows on the warm, moist dirt. Brett Share this post Link to post Share on other sites
