I've been having an intermittant problem where the 3-amp fuse on the circuit board keeps burning out. Lately, the problem has occurred in the late afternoon (3-7pm) such that when I replace the fuse, it will last for 3-4 minutes before blowing again. If I wait until late in the evening to turn on the air conditioning (say 10:30pm), it is likely to run all night without issue.

I have had someone out numerous times. He has completely changed the circuit board. After taking a second look at the exterior unit, we found that the contacter was going bad. The exterior unit was about 20 years old, and the compressor was also starting to go, and I have a 8.5 months pregnant wife -- so I gave him the go-ahead to replace the A/C unit and the coils inside the furnace. I just wanted it to work at this point!

He installed in Monday by 3pm, and it ran until about 5pm the next day, when once again the 3-amp fuse blew. I replaced it twice and same result, blows in five minutes or so.

So I've replaced the circuit board, the entire exterior unit. What else could it be? Could it be the 24V transformer or the thermostat? Or a wiring issue? I've run the blower without the A/C for long stretches without an issue during this mess, too. If it is a wiring issue, do I need a licensed electrician to look at it?

Any thoughts would be appreciated -- I'll pass them on to the technician who will come today or tomorrow.