I have a Carrier Weathermaker 8000 (model # is 58WAV075-101HC), NOT a XHB123D (only choice I could find). My problem is that every so often (once -twice a week) the air blowing out is cold. I observed the problem to be this...When the furnace igniter attemots to light up 2-3 times, the unit won't fire up and cold air just starts to blow thru the vents. If I turn the thermostat to OFF and turn it back on, it works again after a few minutes. Is this something major or expensive to fix, or is it something reasonable? My unit was made in 1993. I am very concerned because it is starting to happen more frequently lately...Please help! I appreciate anyone that can assist me.

Heating & Cooling - Carrier - XHB123D X/Y Series Heat/Cool Air Conditioner