Hi, my Google travels have led me here and I hope some of you wise ones can help. First of all I am not an HVAC guy by any stretch, but I do happen to be an electronics tech.

I have a Carrier 9200 furnace that's acting funny. Tuesday I came home from work and noticed the upstairs was hot, checked the t-stat and it showed that the a/c was on, but got nothing. Checked to see that the outside condenser fan was not running, the breaker for which was not tripped.

Called our LP provider for a service visit, next morning he came by checked everything out and discovered a blown 3A fuse on the fan pcb. He replaced it (even leaving a spare one) and all was well when my wife left the house (I wasn't home).

Came home after work, and nada, same thing as the day before. Went and checked the fuse and noticed he replaced it with a 5A fuse. This fuse was not blown, but still no condenser fan and the t-stat definitely showed a/c as being on.

Here's my educated guess as to what happened: The initial 3A fuse blew due to a possible power surge, the 5A fuse worked for a while but after a few cycles the extra current draw took out the CPU on the fan board (the fuse is tied to that chip).

Does this sound reasonable? They want to replace the fan pcb which is quite expensive.

Any ideas/insight/recommendations would be great!

Thanks for your time.