how to add c wire to heat pump ac unit (only have wires with nuts)
The C terminal connection in your furnace is denoted by the part of the wiring diagram that I have highlighted in blue as shown below. In fact the furnace diagram shows that these wires in the furnace itself are blue (BLU) colored as well.

You will have to remove that taped up wire bundle to ascertain if there is one wire in the cable from the thermostat that is not used. If so then the it can be re-assigned to be the C function to the thermostat. At the furnace end that re-assigned wire will have to be connected in with the wires as highlighted in blue as above. The connection may entail pig tailing into the existing furnace's blue wires. For example at terminal #3 of the SOLID STATE TIME DELAY module.

It is possible to purchase push on terminals that adapt a male terminal out to two terminals. (See the adjacent connections on terminal #2 of the module). Using an adapter like this would allow you to make your C connection without having to cut into the furnace wires.

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