The contractor who installed my central air didn't put a 2 speed motor on the furnace blower. He said he could put a sheve on that would work both for heating and cooling. But when the weather is below 40 degrees the furnace comes on and then shuts off after about 10 seconds. The second time it will stay running. I think the fan is running too fast and the furnace temperature is too low for the fan switch. I would like to put a 2 speed motor on the furnace, but I'm not sure how to size the sheve so the blower speed will be right for both heating and cooling. Any help appreciated.
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