I have a Trane 1200 xl, age unknown. When the air kicks on, the fan on the compressor unit (outside) runs immediately. It seems to not engage the compressor, though. Then, I'll hear a heavy electrical thump, like a sudden draw on amperage as if the compressor is starting. But, it only lasts for about a second, then stops. It will do this about once a minute for 5 or 10 minutes. Then, it will do it again, but the compressor will kick on and I'll be able to hear the heavier working of the unit. When working, it seems to cool fine- air out the vents is about 15 degrees cooler than ambient. This is a kind of intermittent problem, but becoming more frequent (every day, but not every cycle). Any ideas? The breaker at the main box was tripped once about 3 weeks ago, but not since. Been in the house 6 years.