Change the furnace filter. Make sure you use a cheap one when air conditioning, as the better ones restrict airflow when they filter out so much stuff and then plug up, not allowing enough air to pass over the cooling coil in the furnace's air plenum. Turn the A/C off for a few hours (with only the furnace fan on if possible) to melt the ice off the cooling unit inside the furnace.
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Change the furnace filter. Make sure you use a cheap one when air conditioning, as the better ones restrict airflow when they filter out so much stuff and then plug up, not allowing enough air to pass over the cooling coil in the furnace's air plenum. Turn the A/C off for a few hours (with only the furnace fan on if possible) to melt the ice off the cooling unit inside the furnace.