I have a window a/c unit that stopped working. The fan only hummed. I replaced the capacitor and then the unit starts normally, but after about 5 minutes the compressor shuts down, apparently due to overheating. The fan continues to run. It takes about 15 minutes for the compressor to cool down and reset. I was thinking low on refridgerant, but the compressor does not freeze up, but rather heats up. When the unit is first turned on it has cold air blowing.