I am installing a new rth11b on a older rudd hvac unit and I am running into a problem. It calls for a 4 or 5 wire. Their was 5 wires coming off the old unit. 2 yellow 1 red 1 green 1 blue.
I looked at the hvac unit on the roof and the 2 yellow wires go to the same place . Theirt is only 4 wires at the hvac. This is a heat pump can anyone help me

Did you try peeling back some of the outer wire jacket to see if the 5th wire is there? Unusual that 2 wires are used to do the job of 1 (yellow). You can probably use one of them for something else if you can distinguish one from the other at both ends.