My Trane Unit upstairs is not working. Temp reading 80, we usually run it at 74. There is PVC pipe on outside with PVC plug with a small round filter apparatus attached. The last time the A/C guy was here, he pulled it out threw some bleach in it. 5 min service call and $90 later, the unit was working. I really do not want a repeat. The outside unit was whistling but has stopped. Please help