My roughly 15 year old, Carrier unit is having a problem. During the day the furnace works just fine. Sometimes in the middle of the night I wake up to it blowing cold air out. Every evening I have my thermostat set at 68 degrees, but sometimes when I wake up it is 66 and cold air is blowing from the vents. I can't seem to understand why it is only during the middle of the night.
I have my unit serviced every year, so maintenance is constant. What could this be? Does it sound like something "easy" to fix, or very expensive? All of my techs have told me that I should have many years of life remaining on this unit. Is this thing ready to be replaced, or is this worth fixing?
I appreciate anyone that can take a moment to help me. I can give you more info if needed.
Does it have a viewing glass on the lower furnace door? If so you need to look in there and count the flashing LED blinks WHEN the problem is happening. Then look at the legend on it to see the code and post it here. Be careful as Carrier codes are short and long blinks to get the right digits/code. Make sure you count them correctly and read the label. Code 13 canbe 31 if viewed wrong.