ac froze up when fan on low speed.
Exactly twice my a/c has frozen up.Once last year and just this weekend. Both times it was very hot and humid and the unit ran all day trying to keep up and at some point the fan speed was set to low...
Forum Discussion
TXiceman wrote:3PuttNut wrote:
Low refrigerant can also cause the coils to freeze up.
Actually this is the least likely cause of an evaporator coil icing.
The compressor on these small units are what is know as a positive displacement or PD compressor. This means that it pumps a relatively constant volume of refrigerant on each revolution of the shaft.
With the fan on low speed, there is a lesser amount of refrigerant vaporized in the evaporator. The compressor keeps trying to pump the same volume, so the pressure drops in the evaporator to the point that the specific volume (this is the reciprocal of the density of the vapor) of the refrigerant increases to the point that the volume will satisfy the compressor. As the pressure in the coil drops, the temperature drops due to the properties of the refrigerant.
You let the pressure drop to the point that the coil temperature drops below the freeze point of water and the coil is iced or frozen.
I wish that the manufacturers would do away with the low speed on the RV units.
Ken
Very few RV AC units have roof mounted controls. IF you have roof mounted controls, you MUST leave it on Hi Cool in high ambient and hi humidity conditions to prevent freeze up. MOST RV units have a wall tstat and IF they have a wall tstat, they have a freeze sensor mounted in the evap coil. If installed correctly and functioning, the AC can NEVER freeze up from any parameter. So, if the OP has a wall tstat, he needs to check and verify the freeze sensor is indeed in the evap coil. Doug
