My furnace is a carrier and it is pretty old. It works most of the time , but it seems to blow cold air every time it rains and once is dries up it works fine again. I need to either buy a new one or get this one fixed before winter sets in. any suggestions?

Is this a carrier gas packaged unit(it all sets outside as one unit)? If so the older style used a spark ignition and if you let water get in the bottom of the unit it would ground out the electrode and it would not spark at the pilot assembly. You need to check to see how water is getting inside the unit.