I am installing a hard start kit on a heat pump and there are three capacitors.How do I tell which is the run capacitor?There is a large round one and two small oval ones that are connected directly to the fan and compressor.

A start capacitor is black plastic and round, the oval capacitors are the run capacitors, follow the wires to the respective motor or compressor to determine what is the correct capacitor, the one with the highest value or mfd or uf is the capacitor for the compressor.If the large round capacitor is silver then this will be the one for the compressor.
If both capacitors go to the compressor then you would treat them as one for the purpose of adding a start kit. Good luck, Mike