EcoRenovator - View Single Post - Reverse air conditioner freeze up problem

MN Renovator · 10-26-14, 07:27 AM

The dew point is high.
57 degrees F and 64% humidity means that you will have dew at 45 degrees F. Once that wet coil reaches the freezing temperature and you've got a very quickly frosting coil.

I'd say increase the blower speed, but you are already on high. The only other suggestion that I could give you was from a case study done by the DOE that suggested that much of the air exhausted from the evaporator coil of window air conditioners gets cycled back through the coil again because of the supply and return air being in such close proximity. Since you took off the cover, the louvers that would usually push this air away from the unit aren't there. I'd suggest making a makeshift duct of sorts or something else to reduce the amount of air leaving the blower from getting back to the coil, otherwise you are inviting the frost. Something as simple as a cardboard sheet sticking out a few feet between the top and bottom of the coil could make a big difference

It looks like what you need to do is install a temperature sensor that shuts off the compressor and leaves the fan running when the coil gets near freezing to give it a chance to blow the warmer air over and allow it to defrost. With temperatures well above freezing and with the coil not completely frosted over, the defrost cycle would probably only take a few minutes. Cheaper heat pumps usually use a timer, I'd imagine some trial and error over the amount of time the compressor runs and the amount of compressor off time needed could be figured out to develop a crude but useful defrost system.

Good luck.

10-26-14, 07:27 AM	#2
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	The dew point is high. 57 degrees F and 64% humidity means that you will have dew at 45 degrees F. Once that wet coil reaches the freezing temperature and you've got a very quickly frosting coil. I'd say increase the blower speed, but you are already on high. The only other suggestion that I could give you was from a case study done by the DOE that suggested that much of the air exhausted from the evaporator coil of window air conditioners gets cycled back through the coil again because of the supply and return air being in such close proximity. Since you took off the cover, the louvers that would usually push this air away from the unit aren't there. I'd suggest making a makeshift duct of sorts or something else to reduce the amount of air leaving the blower from getting back to the coil, otherwise you are inviting the frost. Something as simple as a cardboard sheet sticking out a few feet between the top and bottom of the coil could make a big difference It looks like what you need to do is install a temperature sensor that shuts off the compressor and leaves the fan running when the coil gets near freezing to give it a chance to blow the warmer air over and allow it to defrost. With temperatures well above freezing and with the coil not completely frosted over, the defrost cycle would probably only take a few minutes. Cheaper heat pumps usually use a timer, I'd imagine some trial and error over the amount of time the compressor runs and the amount of compressor off time needed could be figured out to develop a crude but useful defrost system. Good luck.