Lennox XP19 air to air heat pump freezing up

My lennox XP19 air to air heat pump is located outside. We had some freezing rain and the units drain holes plugged up causing ice to build up inside the unit to a depth of 12 inches. Does anyone know how to prevent this from happening in cold winter climates like Southern Ontario. This is an obvious design flaw for this unit. The unit has been installed correctly at the correct height and is level. The unit drains well as long as the drain holes are not plugged with ice.
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On Jan 8, 9:56 am, snipped-for-privacy@xplornet.com wrote:

Periodically heat pumps go into a defrost mode. This is to keep them clear of ice. While in defrost the unit runs as if it is in the ac mode but without the outside fan for a minute or two. So the outside unit gets hot pretty quickly. I would check to make sure yours is doing so correctly before condeming the design. Sometimes it is triggered by a sensor and sometimes it is just a timed event. There is usually a control board for the defrost and the unit can often be put into the defrost mode for testing by jumping something. There is a lot of high voltage in the outside unit so don't mess with it unless you have some experience with that sort of thing.
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Thanks for the suggestion, I did have the technician check the defrost cycle and he tells me it is working fine. The water just can't run out the 8 small 1/2 inch drain holes in the bottom of the unit if they are plugged with ice. This resulted in a continual build up of ice inside the unit in sub-freezing temperatures. The block of ice he took out of the unit yesterday was 12 inches X 18 inches in size. Maybe it was a rare occurance because of the temperature and freezing rain we had that plugged up the drainage holes.
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Some can have the frequency of the defrost cycle increased. I suspect that even southern Ontario is on the upper limit for a heat pump and that may contribute as well. What's your backup heat?

Thanks for the suggestion, I did have the technician check the defrost cycle and he tells me it is working fine. The water just can't run out the 8 small 1/2 inch drain holes in the bottom of the unit if they are plugged with ice. This resulted in a continual build up of ice inside the unit in sub-freezing temperatures. The block of ice he took out of the unit yesterday was 12 inches X 18 inches in size. Maybe it was a rare occurance because of the temperature and freezing rain we had that plugged up the drainage holes.
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snipped-for-privacy@xplornet.com wrote:

gparsneau;
Have your HVAC technition check and adjust the timing to 30 minutes. What that will accomplish is the heat pump [while running] will check the defrost sensor every 30 minutes, and if needed, will enter defrost. Generally after 10 minutes during defrost it will go back into heating mode even if the coil hasn't completely defrosted. [10 minutes if default and can not be changed.] See if that helps.
--
Zyp



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Have your technician check the defrost termination temperature. They set them at 50º at the factory. In our area we've been setting them at 70º. The available termination temperatures are 50º, 70º, 90º and 100º. The higher the termination temperature the more energy will be used during defrost but the defrost should be more complete.

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YOUNG GUN had written this in response to http://www.thestuccocompany.com/hvac/Lennox-XP19-air-to-air-heat-pump-freezing-up-29838-.htm :
I've worked on a few of these systems. I would recommend increasing the defrost temperature to 90 degrees. As well I would have the control board and sensors replaced. Lennox is having some issues with the original boards and sensors and have come out with a replacement kit. ------------------------------------- snipped-for-privacy@xplornet.com wrote:

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